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metroid:disassembly:game_engine_page

The game engine bank contains most of the code for the game engine.

; -------------------
; METROID source code
; -------------------
; MAIN PROGRAMMERS
;     HAI YUKAMI
;   ZARU SOBAJIMA
;    GPZ SENGOKU
;    N.SHIOTANI
;     M.HOUDAI
; (C) 1986 NINTENDO
;
; Disassembled, reconstructed and commented
; by SnowBro [Kent Hansen] <kentmhan@online.no>
; Continued by Dirty McDingus (nmikstas@yahoo.com)
; Can be reassembled using Ophis.
; A work in progress.
;Last updated: 3/9/2010

;Hosted on wiki.metroidconstruction.com, with possible additions by wiki contributors.

;Game engine (memory page 7)

.org $C000

.include "MetroidDefines.txt"

;-------------------------------------[ Forward declarations ]--------------------------------------

.alias ObjectAnimIndexTbl       $8572
.alias FramePtrTable            $860B
.alias PlacePtrTable            $86DF
.alias StarPalSwitch            $8AC7
.alias SamusEnterDoor           $8B13
.alias AreaPointers             $9598
.alias AreaRoutine              $95C3
.alias EnemyHitPointTbl         $962B
.alias EnemyInitDelayTbl        $96BB
.alias DecSpriteYCoord          $988A
.alias NMIScreenWrite           $9A07
.alias EndGamePalWrite          $9F54
.alias SpecItmsTable            $9598
.alias CopyMap                  $A93E
.alias SoundEngine              $B3B4

;----------------------------------------[ Start of code ]------------------------------------------

;This routine generates pseudo random numbers and updates those numbers
;every frame. The random numbers are used for several purposes including
;password scrambling and determinig what items, if any, an enemy leaves
;behind after it is killed.

RandomNumbers:
LC000:  txa                             ;               
LC001:  pha                             ;
LC002:  ldx #$05                        ;
LC004:* lda RandomNumber1               ;
LC006:  clc                             ;
LC007:  adc #$05                        ;
LC009:  sta RandomNumber1               ;2E is increased by #$19 every frame and-->
LC00B:  lda RandomNumber2               ;2F is increased by #$5F every frame.                   
LC00D:  clc                             ;
LC00E:  adc #$13                        ;
LC010:  sta RandomNumber2               ;
LC012:  dex                             ;
LC013:  bne -                           ;
LC015:  pla                             ;
LC016:  tax                             ;
LC017:  lda RandomNumber1               ;
LC019:  rts                             ;

;------------------------------------------[ Startup ]----------------------------------------------

Startup:
LC01A:  lda #$00                        ;
LC01C:  sta MMC1Reg1                    ;Clear bit 0. MMC1 is serial controlled
LC01F:  sta MMC1Reg1                    ;Clear bit 1
LC022:  sta MMC1Reg1                    ;Clear bit 2
LC024:  sta MMC1Reg1                    ;Clear bit 3
LC027:  sta MMC1Reg1                    ;Clear bit 4 
LC02B:  sta MMC1Reg2                    ;Clear bit 0
LC02E:  sta MMC1Reg2                    ;Clear bit 1
LC031:  sta MMC1Reg2                    ;Clear bit 2
LC034:  sta MMC1Reg2                    ;Clear bit 3
LC037:  sta MMC1Reg2                    ;Clear bit 4 
LC03A:  jsr MMCWriteReg3                ;($C4FA)Swap to PRG bank #0 at $8000
LC03D:  dex                             ;X = $FF
LC03E:  txs                             ;S points to end of stack page

;Clear RAM at $000-$7FF.
LC03F:  ldy #$07                        ;High byte of start address.
LC041:  sty $01                         ;
LC043:  ldy #$00                        ;Low byte of start address.
LC045:  sty $00                         ;$0000 = #$0700
LC047:  tya                             ;A = 0
LC048:* sta ($00),y                     ;clear address
LC04A:  iny                             ;
LC04B:  bne -                           ;Repeat for entire page.
LC04D:  dec $01                         ;Decrement high byte of address.
LC04F:  bmi +                           ;If $01 < 0, all pages are cleared.
LC051:  ldx $01                         ;
LC053:  cpx #$01                        ;Keep looping until ram is cleared.
LC055:  bne -                           ;

;Clear cartridge RAM at $6000-$7FFF.
LC057:* ldy #$7F                        ;High byte of start address.
LC059:  sty $01                         ;
LC05B:  ldy #$00                        ;Low byte of start address.
LC05D:  sty $00                         ;$0000 points to $7F00
LC05F:  tya                             ;A = 0
LC060:* sta ($00),y                     ;
LC062:  iny                             ;Clears 256 bytes of memory before decrementing to next-->
LC063:  bne -                           ;256 bytes.
LC065:  dec $01                         ;
LC067:  ldx $01                         ;Is address < $6000?-->
LC069:  cpx #$60                        ;If not, do another page.
LC06B:  bcs -                           ; 

LC06D:  lda #%00001110                  ;Verticle mirroring.
                                        ;H/V mirroring (As opposed to one-screen mirroring).
                                        ;Switch low PRGROM area during a page switch.
                                        ;16KB PRGROM switching enabled.
                                        ;8KB CHRROM switching enabled.
LC06F:  sta MMCReg0Cntrl                ;

LC071:  lda #$00                        ;Clear bits 3 and 4 of MMC1 register 3.
LC073:  sta SwitchUpperBits             ;

LC075:  ldy #$00                        ;
LC077:  sty ScrollX                     ;ScrollX = 0
LC079:  sty ScrollY                     ;ScrollY = 0
LC07B:  sty PPUScroll                   ;Clear hardware scroll x
LC07E:  sty PPUScroll                   ;Clear hardware scroll y
LC081:  iny                             ;Y = #$01
LC082:  sty GameMode                    ;Title screen mode
LC084:  jsr ClearNameTables             ;($C158)
LC087:  jsr EraseAllSprites             ;($C1A3)

LC08A:  lda #%10010000                  ;NMI = enabled
                                        ;Sprite size = 8x8
                                        ;BG pattern table address = $1000
                                        ;SPR pattern table address = $0000
                                        ;PPU address increment = 1
                                        ;Name table address = $2000
LC08C:  sta PPUControl0                 ;
LC08F:  sta PPUCNT0ZP                   ;

LC091:  lda #%00000010                  ;Sprites visible = no
                                        ;Background visible = no
                                        ;Sprite clipping = yes
                                        ;Background clipping = no
                                        ;Display type = color
LC093:  sta PPUCNT1ZP                   ;

LC095:  lda #$47                        ;
LC097:  sta MirrorCntrl                 ;Prepare to set PPU to vertical mirroring.
LC099:  jsr PrepVertMirror              ;($C4B2)

LC09C:  lda #$00                        ;
LC09E:  sta DMCCntrl1                   ;PCM volume = 0 - disables DMC channel
LC0A1:  lda #$0F                        ;
LC0A3:  sta APUCommonCntrl0             ;Enable sound channel 0,1,2,3

LC0A6:  ldy #$00                        ;
LC0A8:  sty TitleRoutine                ;Set title routine and and main routine function-->
LC0AA:  sty MainRoutine                 ;pointers equal to 0.
LC0AC:  lda #$11                        ;
LC0AE:  sta RandomNumber1               ;Initialize RandomNumber1 to #$11
LC0B0:  lda #$FF                        ;
LC0B2:  sta RandomNumber2               ;Initialize RandomNumber2 to #$FF

LC0B4:  iny                             ;Y = 1
LC0B5:  sty SwitchPending               ;Prepare to switch page 0 into lower PRGROM.
LC0B7:  jsr CheckSwitch                 ;($C4DE)
LC0BA:  bne WaitNMIEnd                  ;Branch always

;-----------------------------------------[ Main loop ]----------------------------------------------

;The main loop runs all the routines that take place outside of the NMI.

MainLoop:
LC0BC:  jsr CheckSwitch                 ;($C4DE)Check to see if memory page needs to be switched.
LC0BF:  jsr UpdateTimer                 ;($C266)Update Timers 1, 2 and 3.
LC0C2:  jsr GoMainRoutine               ;($C114)Go to main routine for updating game.
LC0C5:  inc FrameCount                  ;Increment frame counter.
LC0C7:  lda #$00                        ;
LC0C9:  sta NMIStatus                   ;Wait for next NMI to end.

WaitNMIEnd:
LC0CB:  tay                             ;
LC0CC:  lda NMIStatus                   ;
LC0CE:  bne +                           ;If nonzero, NMI has ended. Else keep waiting.
LC0D0:  jmp WaitNMIEnd                  ;

LC0D3:* jsr RandomNumbers               ;($C000)Update pseudo random numbers.
LC0D6:  jmp MainLoop                    ;($C0BC)Jump to top of subroutine.

;-------------------------------------[ Non-Maskable Interrupt ]-------------------------------------

;The NMI is called 60 times a second by the VBlank signal from the PPU. When the
;NMI routine is called, the game should already be waiting for it in the main 
;loop routine in the WaitNMIEnd loop.  It is possible that the main loop routine
;will not be waiting as it is bogged down with excess calculations. This causes
;the game to slow down.

NMI:
LC0D9:  php                             ;Save processor status, A, X and Y on stack.
LC0DA:  pha                             ;Save A.
LC0DB:  txa                             ;
LC0DC:  pha                             ;Save X.
LC0DD:  tya                             ;
LC0DE:  pha                             ;Save Y.
LC0DF:  lda #$00                        ;
LC0E1:  sta SPRAddress                  ;Sprite RAM address = 0.
LC0E4:  lda #$02                        ;
LC0E6:  sta SPRDMAReg                   ;Transfer page 2 ($200-$2FF) to Sprite RAM.
LC0E9:  lda NMIStatus                   ;
LC0EB:  bne ++                          ;Skip if the frame couldn't finish in time.
LC0ED:  lda GameMode                    ;
LC0EF:  beq +                           ;Branch if mode=Play.
LC0F1:  jsr NMIScreenWrite              ;($9A07)Write end message on screen(If appropriate).
LC0F4:* jsr CheckPalWrite               ;($C1E0)Check if palette data pending.
LC0F7:  jsr CheckPPUWrite               ;($C2CA)check if data needs to be written to PPU.
LC0FA:  jsr WritePPUCtrl                ;($C44D)Update $2000 & $2001.
LC0FD:  jsr WriteScroll                 ;($C29A)Update h/v scroll reg.
LC100:  jsr ReadJoyPads                 ;($C215)Read both joypads.
LC103:* jsr SoundEngine                 ;($B3B4)Update music and SFX.
LC106:  jsr UpdateAge                   ;($C97E)Update Samus' age.
LC109:  ldy #$01                        ; NMI = finished.
LC10B:  sty NMIStatus                   ;
LC10D:  pla                             ;Restore Y.
LC10E:  tay                             ;
LC10F:  pla                             ;Restore X.
LC110:  tax                             ;
LC111:  pla                             ;restore A.
LC112:  plp                             ;Restore processor status flags.
LC113:  rti                             ;Return from NMI.

;----------------------------------------[ GoMainRoutine ]-------------------------------------------

;This is where the real code of each frame is executed.
;MainRoutine or TitleRoutine (Depending on the value of GameMode)
;is used as an index into a code pointer table, and this routine
;is executed.

GoMainRoutine:
LC114:  lda GameMode                    ;0 if game is running, 1 if at intro screen.
LC116:  beq +                           ;Branch if mode=Play.
LC118:  jmp $8000                       ;Jump to $8000, where a routine similar to the one-->
                                        ;below is executed, only using TitleRoutine instead
                                        ;of MainRoutine as index into a jump table.
LC11B:* lda Joy1Change                  ;
LC11D:  and #$10                        ;Has START been pressed?-->
LC11F:  beq +++                         ;if not, execute current routine as normal.

LC121:  lda MainRoutine                 ;
LC123:  cmp #$03                        ;Is game engine running?-->
LC125:  beq +                           ;If yes, check for routine #5 (pause game).
LC127:  cmp #$05                        ;Is game paused?-->
LC129:  bne +++                         ;If not routine #5 either, don't care about START being pressed.
LC12B:  lda #$03                        ;Otherwise, switch to routine #3 (game engine).
LC12D:  bne ++                          ;Branch always.
LC12F:* lda #$05                        ;Switch to pause routine.
LC131:* sta MainRoutine                 ;(MainRoutine = 5 if game paused, 3 if game engine running).
LC133:  lda GamePaused                  ;
LC135:  eor #$01                        ;Toggle game paused.
LC137:  sta GamePaused                  ;
LC139:  jsr PauseMusic                  ;($CB92)Silences music while game paused.

LC13c:* lda MainRoutine                 ;
LC13E:  jsr ChooseRoutine               ;($C27C)Use MainRoutine as index into routine table below.

;Pointer table to code.

LC141:  .word AreaInit                  ;($C801)Area init.
LC143:  .word MoreInit                  ;($C81D)More area init.
LC145:  .word SamusInit                 ;($C8D1)Samus init.
LC147:  .word GameEngine                ;($C92B)Game engine.
LC149:  .word GameOver                  ;($C9A6)Display GAME OVER.
LC14B:  .word PauseMode                 ;($C9B1)Pause game.
LC14D:  .word GoPassword                ;($C9C4)Display password.
LC14F:  .word IncrementRoutine          ;($C155)Just advances to next routine in table.
LC151:  .word SamusIntro                ;($C9D7)Intro.
LC153:  .word WaitTimer                 ;($C494)Delay.

IncrementRoutine:
LC155:  inc MainRoutine                 ;Increment to next routine in above table.
LC157:  rts                             ;

;-------------------------------------[ Clear name tables ]------------------------------------------

ClearNameTables:
LC158:  jsr ClearNameTable0             ;($C16D)Always clear name table 0 first.
LC15B:  lda GameMode                    ;
LC15D:  beq +                           ;Branch if mode = Play.
LC15F:  lda TitleRoutine                ;
LC161:  cmp #$1D                        ;If running the end game routine, clear-->
LC163:  beq ++                          ;name table 2, else clear name table 1.
LC165:* lda #$02                        ;Name table to clear + 1 (name table 1).
LC167:  bne +++                         ;Branch always.
LC169:* lda #$03                        ;Name table to clear + 1 (name table 2).
LC16B:  bne ++                          ;Branch always.

ClearNameTable0:
LC16D:* lda #$01                        ;Name table to clear + 1 (name table 0).
LC16F:* sta $01                         ;Stores name table to clear.
LC171:  lda #$FF                        ;
LC173:  sta $00                         ;Value to fill with.

ClearNameTable:
LC175:  ldx PPUStatus                   ;Reset PPU address latch.
LC178:  lda PPUCNT0ZP                   ;
LC17A:  and #$FB                        ;PPU increment = 1.
LC17C:  sta PPUCNT0ZP                   ;
LC17E:  sta PPUControl0                 ;Store control bits in PPU.
LC181:  ldx $01                         ;
LC183:  dex                             ;Name table = X - 1.
LC184:  lda HiPPUTable,x                ;get high PPU address.  pointer table at $C19F.
LC187:  sta PPUAddress                  ;
LC18A:  lda #$00                        ;Set PPU start address (High byte first).
LC18C:  sta PPUAddress                  ;
LC18F:  ldx #$04                        ;Prepare to loop 4 times.
LC191:  ldy #$00                        ;Inner loop value.
LC193:  lda $00                         ;Fill-value.
LC195:* sta PPUIOReg                    ;
LC198:  dey                             ;
LC199:  bne -                           ;Loops until the desired name table is cleared.-->
LC19B:  dex                             ;It also clears the associated attribute table.
LC19C:  bne -                           ;
LC19E:  rts                             ;

;The following table is used by the above routine for finding
;the high byte of the proper name table to clear.

HiPPUTable:
LC19F:  .byte $20                       ;Name table 0.
LC1A0:  .byte $24                       ;Name table 1.
LC1A1:  .byte $28                       ;Name table 2.
LC1A2:  .byte $2C                       ;Name table 3.

;-------------------------------------[ Erase all sprites ]------------------------------------------

EraseAllSprites:
LC1A3:  ldy #$02                        ;
LC1A5:  sty $01                         ;Loads locations $00 and $01 with -->
LC1A7:  ldy #$00                        ;#$00 and #$02 respectively
LC1A9:  sty $00                         ;
LC1AB:  ldy #$00                        ;
LC1AD:  lda #$F0                        ;
LC1AF:* sta ($00),y                     ;Stores #$F0 in memory addresses $0200 thru $02FF.
LC1B1:  iny                             ; 
LC1B2:  bne -                           ;Loop while more sprite RAM to clear.
LC1B4:  lda GameMode                    ;
LC1B6:  beq Exit101                     ;Exit subroutine if GameMode=Play(#$00)
LC1B8:  jmp DecSpriteYCoord             ;($988A)Find proper y coord of sprites.

Exit101:
LC1BB:  rts                             ;Return used by subroutines above and below.

;---------------------------------------[ Remove intro sprites ]-------------------------------------

;The following routine is used in the Intro to remove the sparkle sprites and the crosshairs
;sprites every frame.  It does this by loading the sprite values with #$F4 which moves the 
;sprite to the bottom right of the screen and uses a blank graphic for the sprite.

RemoveIntroSprites:
LC1BC:  ldy #$02                        ;Start at address $200.
LC1BE:  sty $01                         ;
LC1C0:  ldy #$00                        ;
LC1C2:  sty $00                         ;($00) = $0200 (sprite page)
LC1C4:  ldy #$5F                        ;Prepare to clear RAM $0200-$025F
LC1C6:  lda #$F4                        ;
LC1C8:* sta ($00),y                     ;
LC1CA:  dey                             ;Loop unitl $200 thru $25F is filled with #$F4.
LC1CB:  bpl -                           ;
LC1CD:  lda GameMode                    ;
LC1CF:  beq Exit101                     ; branch if mode = Play.
LC1D1:  jmp DecSpriteYCoord             ;($988A)Find proper y coord of sprites.

;-------------------------------------[Clear RAM $33 thru $DF]---------------------------------------

;The routine below clears RAM associated with rooms and enemies.

ClearRAM_33_DF:
LC1D4:  ldx #$33                        ;
LC1D6:  lda #$00                        ;
LC1D8:* sta $00,x                       ;Clear RAM addresses $33 through $DF.
LC1DA:  inx                             ;
LC1DB:  cpx #$E0                        ;
LC1DD:  bcc -                           ;Loop until all desired addresses are cleared.
LC1DF:  rts                             ;

;--------------------------------[ Check and prepare palette write ]---------------------------------

CheckPalWrite:
LC1E0:  lda GameMode                    ;
LC1E2:  beq +                           ;Is game being played? If so, branch to exit.
LC1E4:  lda TitleRoutine                ;
LC1E6:  cmp #$1D                        ;Is Game at ending sequence? If not, branch
LC1E8:  bcc +                           ;
LC1EA:  jmp EndGamePalWrite             ;($9F54)Write palette data for ending.
LC1ED:* ldy PalDataPending              ;
LC1EF:  bne ++                          ;Is palette data pending? If so, branch.
LC1F1:  lda GameMode                    ;
LC1F3:  beq +                           ;Is game being played? If so, branch to exit.
LC1F5:  lda TitleRoutine                ;
LC1F7:  cmp #$15                        ;Is intro playing? If not, branch.
LC1F9:  bcs +                           ;
LC1FB:  jmp StarPalSwitch               ;($8AC7)Cycles palettes for intro stars twinkle.
LC1FE:* rts                             ;Exit when no palette data pending.

;Prepare to write palette data to PPU.

LC1FF:* dey                             ;Palette # = PalDataPending - 1.
LC200:  tya                             ;
LC201:  asl                             ;* 2, each pal data ptr is 2 bytes (16-bit).
LC202:  tay                             ;
LC203:  ldx $9560,y                     ;X = low byte of PPU data pointer.
LC206:  lda $9561,y                     ;
LC209:  tay                             ;Y = high byte of PPU data pointer.
LC20A:  lda #$00                        ;Clear A.
LC20C:  sta PalDataPending              ;Reset palette data pending byte.

PreparePPUProcess_:
LC20E:  stx $00                         ;Lower byte of pointer to PPU string.
LC210:  sty $01                         ;Upper byte of pointer to PPU string.
LC212:  jmp ProcessPPUString            ;($C30C)Write data string to PPU.

;----------------------------------------[Read joy pad status ]--------------------------------------

;The following routine reads the status of both joypads

ReadJoyPads:
LC215:  ldx #$00                        ;Load x with #$00. Used to read status of joypad 1.
LC217:  stx $01                         ;
LC219:  jsr ReadOnePad                  ;
LC21C:  inx                             ;Load x with #$01. Used to read status of joypad 2.
LC21D:  inc $01                         ;

ReadOnePad:
LC21F:  ldy #$01                        ;These lines strobe the -->       
LC221:  sty CPUJoyPad1                  ;joystick to enable the -->
LC224:  dey                             ;program to read the -->
LC225:  sty CPUJoyPad1                  ;buttons pressed.
        
LC228:  ldy #$08                        ;Do 8 buttons.
LC22A:* pha                             ;Store A.
LC22B:  lda CPUJoyPad1,x                ;Read button status. Joypad 1 or 2.
LC22E:  sta $00                         ;Store button press at location $00.
LC230:  lsr                             ;Move button push to carry bit.
LC231:  ora $00                         ;If joystick not connected, -->
LC233:  lsr                             ;fills Joy1Status with all 1s.
LC234:  pla                             ;Restore A.
LC235:  rol                             ;Add button press status to A.
LC236:  dey                             ;Loop 8 times to get -->
LC237:  bne -                           ;status of all 8 buttons.

LC239:  ldx $01                         ;Joypad #(0 or 1).
LC23B:  ldy Joy1Status,x                ;Get joypad status of previous refresh.
LC23D:  sty $00                         ;Store at $00.
LC23F:  sta Joy1Status,x                ;Store current joypad status.
LC241:  eor $00                         ;
LC243:  beq +                           ;Branch if no buttons changed.
LC245:  lda $00                         ;                       
LC247:  and #$BF                        ;Remove the previous status of the B button.
LC249:  sta $00                         ;
LC24B:  eor Joy1Status,x                ;
LC24D:* and Joy1Status,x                ;Save any button changes from the current frame-->
LC24F:  sta Joy1Change,x                ;and the last frame to the joy change addresses.
LC251:  sta Joy1Retrig,x                ;Store any changed buttons in JoyRetrig address.
LC253:  ldy #$20                        ;
LC255:  lda Joy1Status,x                ;Checks to see if same buttons are being-->
LC257:  cmp $00                         ;pressed this frame as last frame.-->
LC259:  bne +                           ;If none, branch.
LC25B:  dec RetrigDelay1,x              ;Decrement RetrigDelay if same buttons pressed.
LC25D:  bne ++                          ;               
LC25F:  sta Joy1Retrig,x                ;Once RetrigDelay=#$00, store buttons to retrigger.
LC261:  ldy #$08                        ;
LC263:* sty RetrigDelay1,x              ;Reset retrigger delay to #$20(32 frames)-->
LC265:* rts                             ;or #$08(8 frames) if already retriggering.

;-------------------------------------------[ Update timer ]-----------------------------------------

;This routine is used for timing - or for waiting around, rather.
;TimerDelay is decremented every frame. When it hits zero, $2A, $2B and $2C are
;decremented if they aren't already zero. The program can then check
;these variables (it usually just checks $2C) to determine when it's time
;to "move on". This is used for the various sequences of the intro screen,
;when the game is started, when Samus takes a special item, and when GAME
;OVER is displayed, to mention a few examples.

UpdateTimer:
LC266:  ldx #$01                        ;First timer to decrement is Timer2.
LC268:  dec TimerDelay                  ;
LC26A:  bpl DecTimer                    ;
LC26C:  lda #$09                        ;TimerDelay hits #$00 every 10th frame.
LC26E:  sta TimerDelay                  ;Reset TimerDelay after it hits #$00.
LC270:  ldx #$02                        ;Decrement Timer3 every 10 frames.

DecTimer:
LC272:  lda Timer1,x                    ;
LC274:  beq +                           ;Don't decrease if timer is already zero.
LC276:  dec Timer1,x                    ;
LC278:* dex                             ;Timer1 and Timer2 decremented every frame.
LC279:  bpl DecTimer                    ;
LC27B:  rts                             ;

;-----------------------------------------[ Choose routine ]-----------------------------------------

;This is an indirect jump routine. A is used as an index into a code
;pointer table, and the routine at that position is executed. The programmers
;always put the pointer table itself directly after the JSR to ChooseRoutine,
;meaning that its address can be popped from the stack.

ChooseRoutine:
LC27C:  asl                             ;* 2, each ptr is 2 bytes (16-bit).
LC27D:  sty TempY                       ;Temp storage.
LC27F:  stx TempX                       ;Temp storage.
LC281:  tay                             ;
LC282:  iny                             ;
LC283:  pla                             ;Low byte of ptr table address.
LC284:  sta CodePtr                     ;
LC286:  pla                             ;High byte of ptr table address.
LC287:  sta CodePtr+1                   ;
LC289:  lda (CodePtr),y                 ;Low byte of code ptr.
LC28B:  tax                             ;
LC28C:  iny                             ;
LC28D:  lda (CodePtr),y                 ;High byte of code ptr.
LC28F:  sta CodePtr+1                   ;
LC291:  stx CodePtr                     ;
LC293:  ldx TempX                       ;Restore X.
LC295:  ldy TempY                       ;Restore Y.
LC297:  jmp (CodePtr)                   ;

;--------------------------------------[ Write to scroll registers ]---------------------------------

WriteScroll:
LC29A:  lda PPUStatus                   ;Reset scroll register flip/flop
LC29D:  lda ScrollX                     ;
LC29F:  sta PPUScroll                   ;
LC2A2:  lda ScrollY                     ;X and Y scroll offsets are loaded serially.
LC2A4:  sta PPUScroll                   ;
LC2A7:  rts                             ;

;----------------------------------[ Add y index to stored addresses ]-------------------------------

;Add Y to pointer at $0000. 

AddYToPtr00:
LC2A8:  tya                             ;
LC2A9:  clc                             ;Add value stored in Y to lower address-->
LC2AA:  adc $00                         ;byte stored in $00.
LC2AC:  sta $00                         ;
LC2AE:  bcc +                           ;Increment $01(upper address byte) if carry-->
LC2B0:  inc $01                         ;has occurred.
LC2B2:* rts                             ;

;Add Y to pointer at $0002

AddYToPtr02:
LC2B3:  tya                             ;
LC2B4:  clc                             ;Add value stored in Y to lower address-->
LC2B5:  adc $02                         ;byte stored in $02.
LC2B7:  sta $02                         ;
LC2B9:  bcc +                           ;Increment $01(upper address byte) if carry-->
LC2BB:  inc $03                         ;has occurred.
LC2BD:* rts                             ;

;--------------------------------[ Simple divide and multiply routines ]-----------------------------

Adiv32: 
LC2BE:  lsr                             ;Divide by 32.

Adiv16: 
LC2BF:  lsr                             ;Divide by 16.

Adiv8:  
LC2C0:  lsr                             ;Divide by 8.
LC2C1:  lsr                             ;
LC2C2:  lsr                             ;Divide by shifting A right.
LC2C3:  rts                             ;

Amul32: 
LC2C4:  asl                             ;Multiply by 32.

Amul16: 
LC2C5:  asl                             ;Multiply by 16.

Amul8:
LC2C6:  asl                             ;Multiply by 8.
LC2C7:  asl                             ;
LC2C8:  asl                             ;Multiply by shifting A left.
LC2C9:  rts                             ;

;-------------------------------------[ PPU writing routines ]---------------------------------------

;Checks if any data is waiting to be written to the PPU.
;RLE data is one tile that repeats several times in a row.  RLE-Repeat Last Entry

CheckPPUWrite:
LC2CA:  lda PPUDataPending              ;
LC2CC:  beq +                           ;If zero no PPU data to write, branch to exit.
LC2CE:  lda #$A1                        ;                       
LC2D0:  sta $00                         ;Sets up PPU writer to start at address $07A1.
LC2D2:  lda #$07                        ;
LC2D4:  sta $01                         ;$0000 = ptr to PPU data string ($07A1).
LC2D6:  jsr ProcessPPUString            ;($C30C)write it to PPU.
LC2D9:  lda #$00                        ;
LC2DB:  sta PPUStrIndex                 ;PPU data string has been written so the data-->
LC2DE:  sta PPUDataString               ;stored for the write is now erased.
LC2E1:  sta PPUDataPending              ;
LC2E3:* rts                             ;

PPUWrite:
LC2E4:  sta PPUAddress                  ;Set high PPU address.
LC2E7:  iny                             ;
LC2E8:  lda ($00),y                     ;
LC2EA:  sta PPUAddress                  ;Set low PPU address.
LC2ED:  iny                             ;
LC2EE:  lda ($00),y                     ;Get data byte containing rep length & RLE status.
LC2F0:  asl                             ;Carry Flag = PPU address increment (0 = 1, 1 = 32).
LC2F1:  jsr SetPPUInc                   ;($C318)Update PPUCtrl0 according to Carry Flag.
LC2F4:  asl                             ;Carry Flag = bit 6 of byte at ($00),y (1 = RLE).
LC2F5:  lda ($00),y                     ;Get data byte again.
LC2F7:  and #$3F                        ;Keep lower 6 bits as loop counter.
LC2F9:  tax                             ;
LC2FA:  bcc PPUWriteLoop                ;If Carry Flag not set, the data is not RLE.
LC2FC:  iny                             ;Data is RLE, advance to data byte.

PPUWriteLoop:
LC2FD:  bcs +                           ;
LC2FF:  iny                             ;Only inc Y if data is not RLE.
LC300:* lda ($00),y                     ;Get data byte.
LC302:  sta PPUIOReg                    ;Write to PPU.
LC305:  dex                             ;Decrease loop counter.
LC306:  bne PPUWriteLoop                ;Keep going until X=0.
LC308:  iny                             ;
LC309:  jsr AddYToPtr00                 ;($C2A8)Point to next data chunk.

;Write data string at ($00) to PPU.

ProcessPPUString:
LC30C:  ldx PPUStatus                   ;Reset PPU address flip/flop.
LC30F:  ldy #$00                        ;
LC311:  lda ($00),y                     ;
LC313:  bne PPUWrite                    ;If A is non-zero, PPU data string follows,-->
LC315:  jmp WriteScroll                 ;($C29A)Otherwise we're done.

;In: CF = desired PPU address increment (0 = 1, 1 = 32).
;Out: PPU control #0 ($2000) updated accordingly.

SetPPUInc:
LC318:  pha                             ;Preserve A.
LC319:  lda PPUCNT0ZP                   ;
LC31B:  ora #$04                        ;
LC31D:  bcs +                           ;PPU increment = 32 only if Carry Flag set,-->
LC31F:  and #$FB                        ;else PPU increment = 1.
LC321:* sta PPUControl0                 ;
LC323:  sta PPUCNT0ZP                   ;
LC326:  pla                             ;Restore A.
LC327:  rts                             ;

;Erase blasted tile on nametable.  Each screen is 16 tiles across and 15 tiles down.
EraseTile:
LC328:  ldy #$01                        ;
LC32A:  sty PPUDataPending              ;data pending = YES.
LC32C:  dey                             ;
LC32D:  lda ($02),y                     ;
LC32F:  and #$0F                        ;
LC331:  sta $05                         ;# of tiles horizontally.
LC333:  lda ($02),y                     ;
LC335:  jsr Adiv16                      ;($C2BF)/ 16.
LC338:  sta $04                         ;# of tiles vertically.
LC33A:  ldx PPUStrIndex                 ;
LC33D:* lda $01                         ;
LC33F:  jsr WritePPUByte                ;($C36B)write PPU high address to $07A1,PPUStrIndex.
LC342:  lda $00                         ;
LC344:  jsr WritePPUByte                ;($C36B)write PPU low address to $07A1,PPUStrIndex.
LC347:  lda $05                         ;data length.
LC349:  sta $06                         ;
LC34B:  jsr WritePPUByte                ;($C36B)write PPU string length to $07A1,PPUStrIndex.
LC34E:* iny                             ;
LC34F:  lda ($02),y                     ;Get new tile to replace old tile.
LC351:  jsr WritePPUByte                ;($C36B)Write it to $07A1,PPUStrIndex, inc x.
LC354:  dec $06                         ;
LC356:  bne -                           ;Branch if more horizontal tiles to replace.
LC358:  stx PPUStrIndex                 ;
LC35B:  sty $06                         ;
LC35D:  ldy #$20                        ;
LC35F:  jsr AddYToPtr00                 ;($C2A8)Move to next name table line.
LC362:  ldy $06                         ;Store index to find next tile info.
LC364:  dec $04                         ;
LC366:  bne --                          ;Branch if more lines need to be changed on name table.
LC368:  jsr EndPPUString                ;($c376)Finish writing PPU string and exit.

WritePPUByte:
LC36B:  sta PPUDataString,x             ;Store data byte at end of PPUDataString.

NextPPUByte:
LC36E:  inx                             ;PPUDataString has increased in size by 1 byte.
LC36F:  cpx #$4F                        ;PPU byte writer can only write a maximum of #$4F bytes
LC371:  bcc +                           ;If PPU string not full, branch to get more data.
LC373:  ldx PPUStrIndex                 ;

EndPPUString:
LC376:  lda #$00                        ;If PPU string is already full, or all PPU bytes loaded,-->
LC378:  sta PPUDataString,x             ;add #$00 as last byte to the PPU byte string.
LC37B:  pla                             ;
LC37C:  pla                             ;Remove last return address from stack and jump out of-->
LC37D:* rts                             ;PPU writing routines.

;The following routine is only used by the intro routine to load the sprite 
;palette data for the twinkling stars. The following memory addresses are used:
;$00-$01 Destination address for PPU write, $02-$03 Source address for PPU data,
;$04 Temp storage for PPU data byte, $05 PPU data string counter byte,
;$06 Temp storage for index byte.

PrepPPUPaletteString:
LC37E:  ldy #$01                        ;
LC380:  sty PPUDataPending              ;Indicate data waiting to be written to PPU.
LC382:  dey                             ;
LC383:  beq ++++                        ;Branch always

LC385:* sta $04                         ;$04 now contains next data byte to be put into the PPU string.
LC387:  lda $01                         ;High byte of staring address to write PPU data 
LC389:  jsr WritePPUByte                ;($C36B)Put data byte into PPUDataString.
LC38c:  lda $00                         ;Low byte of starting address to write PPU data.
LC38E:  jsr WritePPUByte                ;($C36B)Put data byte into PPUDataString.
LC391:  lda $04                         ;A now contains next data byte to be put into the PPU string.
LC393:  jsr SeparateControlBits         ;($C3C6)Break control byte into two bytes.

LC396:  bit $04                         ;Check to see if RLE bit is set in control byte.-->
LC398:  bvc WritePaletteStringByte      ;If not set, branch to load byte. Else increment index-->
LC39A:  iny                             ;to find repeating data byte.

WritePaletteStringByte:
LC39B:  bit $04                         ;Check if RLE bit is set (again). if set, load same-->
LC39D:  bvs +                           ;byte over and over again until counter = #$00.
LC39F:  iny                             ;Non-repeating data byte. Increment for next byte.
LC3A0:* lda ($02),y                     ;
LC3A2:  jsr WritePPUByte                ;($C36B)Put data byte into PPUDataString.
LC3A5:  sty $06                         ;Temporarily store data index.
LC3A7:  ldy #$01                        ;PPU address increment = 1.
LC3A9:  bit $04                         ;If MSB set in control bit, it looks like this routine might-->
LC3AB:  bpl +                           ;have been used for a software control verticle mirror, but-->
                                        ;the starting address has already been written to the PPU-->
                                        ;string so this section has no effect whether the MSB is set-->
                                        ;or not. The PPU is always incremented by 1.
LC3AD:  ldy #$20                        ;PPU address increment = 32.
LC3AF:* jsr AddYToPtr00                 ;($C2A8)Set next PPU write address.(Does nothing, already set).
LC3B2:  ldy $06                         ;Restore data index to Y.
LC3B4:  dec $05                         ;Decrement counter byte.
LC3B6:  bne WritePaletteStringByte      ;If more bytes to write, branch to write another byte.
LC3B8:  stx PPUStrIndex                 ;Store total length, in bytes, of PPUDataString.
LC3BB:  iny                             ;Move to next data byte(should be #$00).

LC3BC:* ldx PPUStrIndex                 ;X now contains current length of PPU data string.
LC3BF:  lda ($02),y                     ;
LC3C1:  bne ----                        ;Is PPU string done loading (#$00)? If so exit,-->
LC3C3:  jsr EndPPUString                ;($C376)else branch to process PPU byte.

SeparateControlBits:
LC3C6:  sta $04                         ;Store current byte 
LC3C8:  and #$BF                        ;
LC3CA:  sta PPUDataString,x             ;Remove RLE bit and save control bit in PPUDataString.
LC3CD:  and #$3F                        ;
LC3CF:  sta $05                         ;Extract counter bits and save them for use above.
LC3D1:  jmp NextPPUByte                 ;($C36E)

;----------------------------------------[ Math routines ]-------------------------------------------

TwosCompliment:
LC3D4:  eor #$FF                        ;
LC3D6:  clc                             ;Generate twos compliment of value stored in A.
LC3D7:  adc #$01                        ;
LC3D9:  rts                             ;

;The following two routines add a Binary coded decimal (BCD) number to another BCD number.
;A base number is stored in $03 and the number in A is added/subtracted from $03.  $01 and $02 
;contain the lower and upper digits of the value in A respectively.  If an overflow happens after
;the addition/subtraction, the carry bit is set before the routine returns.

Base10Add:
LC3DA:  jsr ExtractNibbles              ;($C41D)Separate upper 4 bits and lower 4 bits.
LC3DD:  adc $01                         ;Add lower nibble to number.
LC3DF:  cmp #$0A                        ;
LC3E1:  bcc +                           ;If result is greater than 9, add 5 to create-->
LC3E3:  adc #$05                        ;valid result(skip #$0A thru #$0F).
LC3E5:* clc                             ;
LC3E6:  adc $02                         ;Add upper nibble to number.
LC3E8:  sta $02                         ;
LC3EA:  lda $03                         ;
LC3EC:  and #$F0                        ;Keep upper 4 bits of HealthLo/HealthHi in A.
LC3EE:  adc $02                         ;
LC3F0:  bcc ++                          ;
LC3F2:* adc #$5F                        ;If upper result caused a carry, add #$5F to create-->
LC3F4:  sec                             ;valid result. Set carry indicating carry to next digit.
LC3F5:  rts                             ;
LC3F6:* cmp #$A0                        ;If result of upper nibble add is greater than #$90,-->
LC3F8:  bcs --                          ;Branch to add #$5F to create valid result.
LC3FA:  rts                             ;

Base10Subtract:
LC3FB:  jsr ExtractNibbles              ;($C41D)Separate upper 4 bits and lower 4 bits.
LC3FE:  sbc $01                         ;Subtract lower nibble from number.
LC400:  sta $01                         ;
LC402:  bcs +                           ;If result is less than zero, add 10 to create-->
LC404:  adc #$0A                        ;valid result.
LC406:  sta $01                         ;
LC408:  lda $02                         ;
LC40A:  adc #$0F                        ;Adjust $02 to account for borrowing.
LC40C:  sta $02                         ;
LC40E:* lda $03                         ;Keep upper 4 bits of HealthLo/HealthHi in A.
LC410:  and #$F0                        ;
LC412:  sec                             ;
LC413:  sbc $02                         ;If result is greater than zero, branch to finish.
LC415:  bcs +                           ;
LC417:  adc #$A0                        ;Add 10 to create valid result.
LC419:  clc                             ;
LC41A:* ora $01                         ;Combine A and $01 to create final value.
LC41C:  rts                             ;

ExtractNibbles:
LC41D:  pha                             ;
LC41E:  and #$0F                        ;Lower 4 bits of value to change HealthLo/HealthHi by.
LC420:  sta $01                         ;
LC422:  pla                             ;
LC423:  and #$F0                        ;Upper 4 bits of value to change HealthLo/HealthHi by.
LC425:  sta $02                         ;
LC427:  lda $03                         ;
LC429:  and #$0F                        ;Keep lower 4 bits of HealthLo/HealthHi in A.
LC42B:  rts                             ;

;---------------------------[ NMI and PPU control routines ]--------------------------------

; Wait for the NMI to end.

WaitNMIPass:    
LC42C:  jsr ClearNMIStat                ;($C434)Indicate currently in NMI.
LC42F:* lda NMIStatus                   ;
LC431:  beq -                           ;Wait for NMI to end.
LC433:  rts                             ;

ClearNMIStat:
LC434:  lda #$00                        ;Clear NMI byte to indicate the game is-->
LC436:  sta NMIStatus                   ;currently running NMI routines.
LC438:  rts                             ;

ScreenOff:
LC439:  lda PPUCNT1ZP                   ;
LC43B:  and #$E7                        ; BG & SPR visibility = off

WriteAndWait:
LC43D:* sta PPUCNT1ZP                   ;Update value to be loaded into PPU control register.

WaitNMIPass_:
LC43F:  jsr ClearNMIStat                ;($C434)Indicate currently in NMI.
LC442:* lda NMIStatus                   ;
LC444:  beq -                           ;Wait for NMI to end before continuing.
LC446:  rts                             ;

ScreenOn:
LC447:  lda PPUCNT1ZP                   ;
LC449:  ora #$1E                        ;BG & SPR visibility = on
LC44B:  bne --                          ;Branch always

;Update the actual PPU control registers.

WritePPUCtrl:
LC44D:  lda PPUCNT0ZP                   ;
LC44F:  sta PPUControl0                 ;
LC452:  lda PPUCNT1ZP                   ;Update PPU control registers.
LC454:  sta PPUControl1                 ;
LC457:  lda MirrorCntrl                 ;
LC459:  jsr PrepPPUMirror               ;($C4D9)Setup vertical or horizontal mirroring.

ExitSub:
LC45C:  rts                             ;Exit subroutines.

;Turn off both screen and NMI.

ScreenNmiOff:
LC45D:  lda PPUCNT1ZP                   ;
LC45F:  and #$E7                        ;BG & SPR visibility = off
LC461:  jsr WriteAndWait                ;($C43D)Wait for end of NMI.
LC464:  lda PPUCNT0ZP                   ;Prepare to turn off NMI in PPU.
LC466:  and #$7F                        ;NMI = off
LC468:  sta PPUCNT0ZP                   ;
LC46A:  sta PPUControl0                 ;Actually load PPU register with NMI off value.
LC46D:  rts                             ;

;The following routine does not appear to be used.

LC46E:  lda PPUCNT0ZP                   ;Enable VBlank.
LC470:  ora #$80                        ;
LC472:  sta PPUCNT0ZP                   ;Write PPU control register 0 and PPU status byte.
LC474:  sta PPUControl0                 ;
LC477:  lda PPUCNT1ZP                   ;Turn sprites and screen on.
LC479:  ora #$1E                        ;
LC47B:  bne --                          ;Branch always.

VBOffAndHorzWrite: 
LC47D:  lda PPUCNT0ZP                   ;
LC47F:  and #$7B                        ;Horizontal write, disable VBlank. 
LC481:* sta PPUControl0                 ;Save new values in the PPU control register-->
LC484:  sta PPUCNT0ZP                   ;and PPU status byte.
LC486:  rts                             ;

NmiOn:
LC487:* lda PPUStatus                   ;
LC48A:  and #$80                        ;Wait for end of VBlank.
LC48C:  bne -                           ;
LC48E:  lda PPUCNT0ZP                   ;
LC490:  ora #$80                        ;Enable VBlank interrupts.
LC492:  bne --                          ;Branch always.

;--------------------------------------[ Timer routines ]--------------------------------------------

;The following routines set the timer and decrement it. The timer is set after Samus dies and
;before the GAME OVER message is dispayed.  The timer is also set while the item pickup music
;is playing.

WaitTimer:
LC494:  lda Timer3                      ;Exit if timer hasn't hit zero yet
LC496:  bne +                           ;
LC498:  lda NextRoutine                 ;Set GameOver as next routine.
LC49A:  cmp #$04                        ;
LC49C:  beq SetMainRoutine              ;Set GoPassword as main routine.
LC49E:  cmp #$06                        ;
LC4A0:  beq SetMainRoutine              ;
LC4A2:  jsr StartMusic                  ;($D92C)Assume power up was picked up and GameEngine-->
LC4A5:  lda NextRoutine                 ;is next routine. Start area music before exiting.

SetMainRoutine:
LC4A7:  sta MainRoutine                 ;Set next routine to run.
LC4A9:* rts                             ;

SetTimer:
LC4AA:  sta Timer3                      ;Set Timer3. Frames to wait is value stored in A*10.
LC4AC:  stx NextRoutine                 ;Save routine to jump to after Timer3 expires.
LC4AE:  lda #$09                        ;Next routine to run is WaitTimer.
LC4B0:  bne SetMainRoutine              ;Branch always.

;-----------------------------------[ PPU mirroring routines ]---------------------------------------

PrepVertMirror:
LC4B2:  nop                             ;
LC4B3:  nop                             ;Prepare to set PPU for vertical mirroring (again).
LC4B4:  lda #$47                        ;

SetPPUMirror:
LC4B6:  lsr                             ;
LC4B7:  lsr                             ;Move bit 3 to bit 0 position.
LC4B8:  lsr                             ;
LC4B9:  and #$01                        ;Remove all other bits.
LC4BB:  sta $00                         ;Store at address $00.
LC4BD:  lda MMCReg0Cntrl                ;
LC4BF:  and #$FE                        ;Load MMCReg0Cntrl and remove bit 0.
LC4C1:  ora $00                         ;Replace bit 0 with stored bit at $00.
LC4C3:  sta MMCReg0Cntrl                ;
LC4C5:  sta MMC1Reg0                    ;
LC4C8:  lsr                             ;
LC4C9:  sta MMC1Reg0                    ;
LC4Cc:  lsr                             ;
LC4CD:  sta MMC1Reg0                    ;
LC4D0:  lsr                             ;Load new configuration data serially-->
LC4D1:  sta MMC1Reg0                    ;into MMC1Reg0.
LC4D4:  lsr                             ;
LC4D5:  sta MMC1Reg0                    ;
LC4D8:  rts                             ;

PrepPPUMirror:
LC4D9:  lda MirrorCntrl                 ;Load MirrorCntrl into A.
LC4DB:  jmp SetPPUMirror                ;($C4B6)Set mirroring through MMC1 chip.

;-----------------------------[ Switch bank and init bank routines ]---------------------------------

;This is how the bank switching works... Every frame, the routine below
;is executed. First, it checks the value of SwitchPending. If it is zero,
;the routine will simply exit. If it is non-zero, it means that a bank
;switch has been issued, and must be performed. SwitchPending then contains
;the bank to switch to, plus one.

CheckSwitch:
LC4DE:  ldy SwitchPending               ;
LC4E0:  beq +                           ;Exit if zero(no bank switch issued). else Y contains bank#+1.
LC4E2:  jsr SwitchOK                    ;($C4E8)Perform bank switch.
LC4E5:  jmp GoBankInit                  ;($C510)Initialize bank switch data.

SwitchOK:
LC4E8:  lda #$00                        ;Reset(so that the bank switch won't be performed-->
LC4EA:  sta SwitchPending               ;every succeeding frame too).
LC4EC:  dey                             ;Y now contains the bank to switch to.
LC4ED:  sty CurrentBank                 ;

ROMSwitch:
LC4EF:  tya                             ;
LC4F0:  sta $00                         ;Bank to switch to is stored at location $00.
LC4F2:  lda SwitchUpperBits             ;Load upper two bits for Reg 3 (they should always be 0).
LC4F4:  and #$18                        ;Extract bits 3 and 4 and add them to the current-->
LC4F6:  ora $00                         ;bank to switch to.
LC4F8:  sta SwitchUpperBits             ;Store any new bits set in 3 or 4(there should be none).

;Loads the lower memory page with the bank specified in A.

MMCWriteReg3:
LC4FA:  sta MMC1Reg3                    ;Write bit 0 of ROM bank #.
LC4FD:  lsr                             ;
LC4FE:  sta MMC1Reg3                    ;Write bit 1 of ROM bank #.
LC501:  lsr                             ;
LC502:  sta MMC1Reg3                    ;Write bit 2 of ROM bank #.
LC505:  lsr                             ;
LC506:  sta MMC1Reg3                    ;Write bit 3 of ROM bank #.
LC509:  lsr                             ;
LC50A:  sta MMC1Reg3                    ;Write bit 4 of ROM bank #.
LC50D:  lda $00                         ;Restore A with current bank number before exiting.
LC50F:* rts                             ;

;Calls the proper routine according to the bank number in A.

GoBankInit:
LC510:  asl                             ;*2 For proper table offset below.
LC511:  tay                             ;
LC512:  lda BankInitTable,y             ;
LC515:  sta $0A                         ;Load appropriate subroutine address into $0A and $0B.
LC517:  lda BankInitTable+1,y           ;
LC51A:  sta $0B                         ;
LC51C:  jmp ($000A)                     ;Jump to appropriate initialization routine.

BankInitTable:
LC51F:  .word InitBank0                 ;($C531)Initialize bank 0.
LC521:  .word InitBank1                 ;($C552)Initialize bank 1.
LC523:  .word InitBank2                 ;($C583)Initialize bank 2.
LC525:  .word InitBank3                 ;($C590)Initialize bank 3.
LC527:  .word InitBank4                 ;($C5B6)Initialize bank 4.
LC529:  .word InitBank5                 ;($C5C3)Initialize bank 5.
LC52B:  .word ExitSub                   ;($C45C)Rts
LC52D:  .word ExitSub                   ;($C45C)Rts
LC52F:  .word ExitSub                   ;($C45C)Rts

;Title screen memory page.

InitBank0:
LC531:  ldy #$00                        ;
LC533:  sty GamePaused                  ;Ensure game is not paused.
LC535:  iny                             ;Y=1.
LC536:  sty GameMode                    ;Game is at title routines.
LC538:  jsr ScreenNmiOff                ;($C45D)Waits for NMI to end then turns it off.
LC53B:  jsr CopyMap                     ;($A93E)Copy game map from ROM to cartridge RAM $7000-$73FF
LC53E:  jsr ClearNameTables             ;($C158)Erase name table data.

LC541:  ldy #$A0                        ;
LC543:* lda $98BF,y                     ;
LC546:  sta $6DFF,y                     ;Loads sprite info for stars into RAM $6E00 thru 6E9F.
LC549:  dey                             ;
LC54A:  bne -                           ;

LC54C:  jsr InitTitleGFX                ;($C5D7)Load title GFX.
LC54F:  jmp NmiOn                       ;($C487)Turn on VBlank interrupts.

;Brinstar memory page.

InitBank1:
LC552:  lda #$00                        ;
LC554:  sta GameMode                    ;GameMode = play.
LC556:  jsr ScreenNmiOff                ;($C45D)Disable screen and Vblank.
LC559:  lda MainRoutine                 ;
LC55B:  cmp #$03                        ;Is game engine running? if so, branch.-->
LC55D:  beq +                           ;Else do some housekeeping first.
LC55F:  lda #$00                        ;
LC561:  sta MainRoutine                 ;Run InitArea routine next.
LC563:  sta InArea                      ;Start in Brinstar.
LC565:  sta GamePaused                  ;Make sure game is not paused.
LC567:  jsr ClearRAM_33_DF              ;($C1D4)Clear game engine memory addresses.
LC56A:  jsr ClearSamusStats             ;($C578)Clear Samus' stats memory addresses.
LC56D:* ldy #$00                        ;
LC56F:  jsr ROMSwitch                   ;($C4EF)Load Brinstar memory page into lower 16Kb memory.
LC572:  jsr InitBrinstarGFX             ;($C604)Load Brinstar GFX.
LC575:  jmp NmiOn                       ;($C487)Turn on VBlank interrupts.

ClearSamusStats:
LC578:  ldy #$0F                        ;
LC57A:  lda #$00                        ;Clears Samus stats(Health, full tanks, game timer, etc.).
LC57C:* sta $0100,y                     ;Load $100 thru $10F with #$00.
LC57F:  dey                             ;
LC580:  bpl -                           ;Loop 16 times.
LC582:  rts                             ;

;Norfair memory page.

InitBank2:
LC583:  lda #$00                        ;GameMode = play.
LC585:  sta GameMode                    ;
LC587:  jsr ScreenNmiOff                ;($C45D)Disable screen and Vblank.
LC58A:  jsr InitNorfairGFX              ;($C622)Load Norfair GFX.
LC58D:  jmp NmiOn                       ;($C487)Turn on VBlank interrupts.

;Tourian memory page.

InitBank3:
LC590:  lda #$00                        ;GameMode = play.
LC592:  sta GameMode                    ;
LC594:  jsr ScreenNmiOff                ;($C45D)Disable screen and Vblank.
LC597:  ldy #$0D                        ;
LC599:* lda MetroidData,y               ;Load info from table below into-->
LC59C:  sta $77F0,y                     ;$77F0 thru $77FD.
LC59F:  dey                             ;
LC5A0:  bpl -                           ;
LC5A2:  jsr InitTourianGFX              ;($C645)Load Tourian GFX.
LC5A5:  jmp NmiOn                       ;($C487)Turn on VBlank interrupts.

;Table used by above subroutine and loads the initial data used to describe
;metroid's behavior in the Tourian section of the game.

MetroidData:
LC5A8:  .byte $F8, $08, $30, $D0, $60, $A0, $02, $04, $00, $00, $00, $00, $00, $00

;Kraid memory page.

InitBank4:
LC5B6:  lda #$00                        ;GameMode = play.
LC5B8:  sta GameMode                    ;
LC5BA:  jsr ScreenNmiOff                ;($C45D)Disable screen and Vblank.
LC5BD:  jsr InitKraidGFX                ;($C677)Load Kraid GFX.
LC5C0:  jmp NmiOn                       ;($C487)Turn on VBlank interrupts.

;Ridley memory page.

InitBank5:
LC5C3:  lda #$00                        ;GameMode = play.
LC5C5:  sta GameMode                    ;
LC5C7:  jsr ScreenNmiOff                ;($C45D)Disable screen and Vblank.
LC5CA:  jsr InitRidleyGFX               ;($C69F)Loag Ridley GFX.
LC5CD:  jmp NmiOn                       ;($C487)Turn on VBlank interrupts.

InitEndGFX:
LC5D0:  lda #$01                        ;
LC5D2:  sta GameMode                    ;Game is at title/end game.
LC5D4:  jmp InitGFX6                    ;($C6C2)Load end game GFX.

InitTitleGFX:
LC5D7:  ldy #$15                        ;Entry 21 in GFXInfo table.
LC5D9:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.

LoadSamusGFX:
LC5DC:  ldy #$00                        ;Entry 0 in GFXInfo table.
LC5DE:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC5E1:  lda JustInBailey                ;
LC5E4:  beq +                           ;Branch if wearing suit
LC5E6:  ldy #$1B                        ;Entry 27 in GFXInfo table.
LC5E8:  jsr LoadGFX                     ;($C7AB)Switch to girl gfx
LC5EB:* ldy #$14                        ;Entry 20 in GFXInfo table.
LC5ED:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC5F0:  ldy #$17                        ;Entry 23 in GFXInfo table.
LC5F2:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC5F5:  ldy #$18                        ;Entry 24 in GFXInfo table.
LC5F7:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC5FA:  ldy #$19                        ;Entry 25 in GFXInfo table.
LC5FC:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC5FF:  ldy #$16                        ;Entry 22 in GFXInfo table.
LC601:  jmp LoadGFX                     ;($C7AB)Load pattern table GFX.

InitBrinstarGFX:
LC604:  ldy #$03                        ;Entry 3 in GFXInfo table.
LC606:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
Lc609:  ldy #$04                        ;Entry 4 in GFXInfo table.
LC60B:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC60E:  ldy #$05                        ;Entry 5 in GFXInfo table.
LC610:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC613:  ldy #$06                        ;Entry 6 in GFXInfo table.
LC615:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC618:  ldy #$19                        ;Entry 25 in GFXInfo table.
LC61A:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC61D:  ldy #$16                        ;Entry 22 in GFXInfo table.
LC61F:  jmp LoadGFX                     ;($C7AB)Load pattern table GFX.

InitNorfairGFX:
LC622:  ldy #$04                        ;Entry 4 in GFXInfo table.
LC624:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC627:  ldy #$05                        ;Entry 5 in GFXInfo table.
LC629:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC62C:  ldy #$07                        ;Entry 7 in GFXInfo table.
LC62E:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC631:  ldy #$08                        ;Entry 8 in GFXInfo table.
LC633:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC636:  ldy #$09                        ;Entry 9 in GFXInfo table.
LC638:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC63B:  ldy #$19                        ;Entry 25 in GFXInfo table.
LC63D:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC640:  ldy #$16                        ;Entry 22 in GFXInfo table.
LC642:  jmp LoadGFX                     ;($C7AB)Load pattern table GFX.

InitTourianGFX:
LC645:  ldy #$05                        ;Entry 5 in GFXInfo table.
LC647:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC64A:  ldy #$0A                        ;Entry 10 in GFXInfo table.
LC64C:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC64F:  ldy #$0B                        ;Entry 11 in GFXInfo table.
LC651:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC654:  ldy #$0C                        ;Entry 12 in GFXInfo table.
LC656:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC659:  ldy #$0D                        ;Entry 13 in GFXInfo table.
LC65B:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC65E:  ldy #$0E                        ;Entry 14 in GFXInfo table.
LC660:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC663:  ldy #$1A                        ;Entry 26 in GFXInfo table.
LC665:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC668:  ldy #$1C                        ;Entry 28 in GFXInfo table.
LC66A:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC66D:  ldy #$19                        ;Entry 25 in GFXInfo table.
LC66F:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC672:  ldy #$16                        ;Entry 22 in GFXInfo table.
LC674:  jmp LoadGFX                     ;($C7AB)Load pattern table GFX.

InitKraidGFX:
LC677:  ldy #$04                        ;Entry 4 in GFXInfo table.
LC679:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC67C:  ldy #$05                        ;Entry 5 in GFXInfo table.
LC67E:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC681:  ldy #$0A                        ;Entry 10 in GFXInfo table.
LC683:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC686:  ldy #$0F                        ;Entry 15 in GFXInfo table.
LC688:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC68B:  ldy #$10                        ;Entry 16 in GFXInfo table.
LC68D:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC690:  ldy #$11                        ;Entry 17 in GFXInfo table.
LC692:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC695:  ldy #$19                        ;Entry 25 in GFXInfo table.
LC697:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC69A:  ldy #$16                        ;Entry 22 in GFXInfo table.
LC69C:  jmp LoadGFX                     ;($C7AB)Load pattern table GFX.

InitRidleyGFX:
LC69F:  ldy #$04                        ;Entry 4 in GFXInfo table.
LC6A1:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6A4:  ldy #$05                        ;Entry 5 in GFXInfo table.
LC6A6:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6A9:  ldy #$0A                        ;Entry 10 in GFXInfo table.
LC6AB:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6AE:  ldy #$12                        ;Entry 18 in GFXInfo table.
LC6B0:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6B3:  ldy #$13                        ;Entry 19 in GFXInfo table.
LC6B5:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6B8:  ldy #$19                        ;Entry 25 in GFXInfo table.
LC6BA:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6BD:  ldy #$16                        ;Entry 22 in GFXInfo table.
LC6BF:  jmp LoadGFX                     ;($C7AB)Load pattern table GFX.

InitGFX6:
LC6C2:  ldy #$01                        ;Entry 1 in GFXInfo table.
LC6C4:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6C7:  ldy #$02                        ;Entry 2 in GFXInfo table.
LC6C9:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6CC:  ldy #$19                        ;Entry 25 in GFXInfo table.
LC6CE:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6D1:  ldy #$16                        ;Entry 22 in GFXInfo table.
LC6D3:  jmp LoadGFX                     ;($C7AB)Load pattern table GFX.

InitGFX7:
LC6D6:  ldy #$17                        ;Entry 23 in GFXInfo table.
LC6D8:  jsr LoadGFX                     ;($C7AB)Load pattern table GFX.
LC6DB:  ldy #$16                        ;Entry 22 in GFXInfo table.
LC6DD:  jmp LoadGFX                     ;($C7AB)Load pattern table GFX.

;The table below contains info for each tile data block in the ROM.
;Each entry is 7 bytes long. The format is as follows:
;byte 0: ROM bank where GFX data is located.
;byte 1-2: 16-bit ROM start address (src).
;byte 3-4: 16-bit PPU start address (dest).
;byte 5-6: data length (16-bit).

GFXInfo:
LC6E0:  .byte $06                       ;[SPR]Samus, items.             Entry 0.
LC6E1:  .word $8000, $0000, $09A0
LC6E7:  .byte $04                       ;[SPR]Samus in ending.          Entry 1.
LC6E8:  .word $8D60, $0000, $0520
LC6EE:  .byte $01                       ;[BGR]Partial font, "The End".  Entry 2.
LC6EF:  .word $8D60, $1000, $0400
LC6F5:  .byte $06                       ;[BGR]Brinstar rooms.           Entry 3.
LC6F6:  .word $9DA0, $1000, $0150
LC6FC:  .byte $05                       ;[BGR]Misc. objects.            Entry 4.
LC6FD:  .word $8D60, $1200, $0450
LC703:  .byte $06                       ;[BGR]More Brinstar rooms.      Entry 5.
LC704:  .word $9EF0, $1800, $0800
LC70A:  .byte $01                       ;[SPR]Brinstar enemies.         Entry 6.
LC70B:  .word $9160, $0C00, $0400
LC711:  .byte $06                       ;[BGR]Norfair rooms.            Entry 7.
LC712:  .word $A6F0, $1000, $0260
LC718:  .byte $06                       ;[BGR]More Norfair rooms.       Entry 8.
LC719:  .word $A950, $1700, $0070
LC71F:  .byte $02                       ;[SPR]Norfair enemies.          Entry 9.
LC720:  .word $8D60, $0C00, $0400
LC726:  .byte $06                       ;[BGR]Tourian rooms.            Entry 10.
LC727:  .word $A9C0, $1000, $02E0
LC72D:  .byte $06                       ;[BGR]More Tourian rooms.       Entry 11.
LC72E:  .word $ACA0, $1200, $0600
LC734:  .byte $06                       ;[BGR]Mother Brain room.        Entry 12.
LC735:  .word $B2A0, $1900, $0090
LC73B:  .byte $05                       ;[BGR]Misc. object.             Entry 13.
LC73C:  .word $91B0, $1D00, $0300
LC742:  .byte $02                       ;[SPR]Tourian enemies.          Entry 14.
LC743:  .word $9160, $0C00, $0400
LC749:  .byte $06                       ;[BGR]More Tourian rooms.       Entry 15.
LC74A:  .word $B330, $1700, $00C0
LC750:  .byte $04                       ;[BGR]Misc. object and fonts.   Entry 16.
LC751:  .word $9360, $1E00, $0200
LC757:  .byte $03                       ;[SPR]Miniboss I enemies.       Entry 17.
LC758:  .word $8D60, $0C00, $0400
LC75E:  .byte $06                       ;[BGR]More Tourian Rooms.       Entry 18.
LC75F:  .word $B3F0, $1700, $00C0
LC765:  .byte $03                       ;[SPR]Miniboss II enemies.      Entry 19.
LC766:  .word $9160, $0C00, $0400
LC76C:  .byte $06                       ;[SPR]Inrto/End sprites.        Entry 20.
LC76D:  .word $89A0, $0C00, $0100
LC773:  .byte $06                       ;[BGR]Title.                    Entry 21.
LC774:  .word $8BE0, $1400, $0500
LC77A:  .byte $06                       ;[BGR]Solid tiles.              Entry 22.
LC77B:  .word $9980, $1FC0, $0040
LC781:  .byte $06                       ;[BGR]Complete font.            Entry 23.
LC782:  .word $B4C0, $1000, $0400
LC788:  .byte $06                       ;[BGR]Complete font.            Entry 24.
LC789:  .word $B4C0, $0A00, $00A0
LC78F:  .byte $06                       ;[BGR]Solid tiles.              Entry 25.
LC790:  .word $9980, $0FC0, $0040
LC796:  .byte $06                       ;[BGR]Complete font.            Entry 26.
LC797:  .word $B4C0, $1D00, $02A0
LC79D:  .byte $06                       ;[SPR]Suitless Samus.           Entry 27.
LC79E:  .word $90E0, $0000, $07B0
LC7A4:  .byte $06                       ;[BGR]Exclaimation point.       Entry 28.
LC7A5:  .word $9890, $1F40, $0010

;--------------------------------[ Pattern table loading routines ]---------------------------------

;Y contains the GFX header to fetch from the table above, GFXInfo.

LoadGFX:
LC7AB:  lda #$FF                        ;
LC7AD:* clc                             ;Every time y decrements, the entry into the table-->
LC7AE:  adc #$07                        ;is increased by 7.  When y is less than 0, A points-->
LC7B0:  dey                             ;to the last byte of the entry in the table.
LC7B1:  bpl -                           ;
LC7B3:  tay                             ;Transfer offset into table to Y.

LC7B4:  ldx #$06                        ;
LC7B6:* lda GFXInfo,y                   ;
LC7B9:  sta $00,x                       ;Copy entries from GFXInfo to $00-$06.
LC7BB:  dey                             ;
LC7BC:  dex                             ;
LC7BD:  bpl -                           ;

LC7BF:  ldy $00                         ;ROM bank containing the GFX data.
LC7C1:  jsr ROMSwitch                   ;($C4EF)Switch to that bank.
LC7C4:  lda PPUCNT0ZP                   ;
LC7C6:  and #$FB                        ;
LC7C8:  sta PPUCNT0ZP                   ;Set the PPU to increment by 1.
LC7CA:  sta PPUControl0                 ;
LC7CD:  jsr CopyGFXBlock                ;($C7D5)Copy graphics into pattern tables.
LC7D0:  ldy CurrentBank                 ;
LC7D2:  jmp ROMSwitch                   ;($C4FE)Switch back to the "old" bank.

;Writes tile data from ROM to VRAM, according to the gfx header data
;contained in $00-$06.

CopyGFXBlock:
LC7D5:  lda $05                         ;
LC7D7:  bne GFXCopyLoop                 ;If $05 is #$00, decrement $06 before beginning.
LC7D9:  dec $06                         ;

GFXCopyLoop:
LC7DB:  lda $04                         ;
LC7DD:  sta PPUAddress                  ;Set PPU to proper address for GFX block write.
LC7E0:  lda $03                         ;
LC7E2:  sta PPUAddress                  ;
LC7E5:  ldy #$00                        ;Set offset for GFX data to 0.
LC7E7:* lda ($01),y                     ;
LC7E9:  sta PPUIOReg                    ;Copy GFX data byte from ROM to Pattern table.
LC7EC:  dec $05                         ;Decrement low byte of data length.
LC7EE:  bne +                           ;Branch if high byte does not need decrementing.
LC7F0:  lda $06                         ;
LC7F2:  beq ++                          ;If copying complete, branch to exit.
LC7F4:  dec $06                         ;Decrement when low byte has reached 0.
LC7F6:* iny                             ;Increment to next byte to copy.
LC7F7:  bne --                          ;
LC7F9:  inc $02                         ;After 256 bytes loaded, increment upper bits of-->
LC7FB:  inc $04                         ;Source and destination addresses.
LC7FD:  jmp GFXCopyLoop                 ;(&C7DB)Repeat copy routine.
LC800:* rts                             ;

;-------------------------------------------[ AreaInit ]---------------------------------------------

AreaInit:
LC801:  lda #$00                        ;
LC803:  sta ScrollX                     ;Clear ScrollX.
LC805:  sta ScrollY                     ;Clear ScrollY.
LC807:  lda PPUCNT0ZP                   ;       
LC809:  and #$FC                        ;Sets nametable address = $2000.
LC80B:  sta PPUCNT0ZP                   ;
LC80D:  inc MainRoutine                 ;Increment MainRoutine to MoreInit.
LC80F:  lda Joy1Status                  ;
LC811:  and #$C0                        ;Stores status of both the A and B buttons.
LC813:  sta ABStatus                    ;Appears to never be accessed.
LC815:  jsr EraseAllSprites             ;($C1A3)Clear all sprite info.
LC818:  lda #$10                        ;Prepare to load Brinstar memory page.
LC81A:  jsr IsEngineRunning             ;($CA18)Check to see if ok to switch lower memory page.

;------------------------------------------[ MoreInit ]---------------------------------------------

MoreInit:
LC81D:  ldy #$01                        ;
LC81F:  sty PalDataPending              ;Palette data pending = yes.
LC821:  ldx #$FF                        ;
LC823:  stx SpareMem75                  ;$75 Not referenced ever again in the game.
LC825:  inx                             ;X=0.
LC826:  stx AtEnding                    ;Not playing ending scenes.
LC829:  stx DoorStatus                  ;Samus not in door.
LC82B:  stx SamusDoorData               ;Samus is not inside a door.
LC82D:  stx UpdatingProjectile          ;No projectiles need to be updated.
LC82F:  txa                             ;A=0.

LC830:* cpx #$65                        ;Check to see if more RAM to clear in $7A thru $DE.
LC832:  bcs +                           ;
LC834:  sta $7A,x                       ;Clear RAM $7A thru $DE.
LC836:* cpx #$FF                        ;Check to see if more RAM to clear in $300 thru $3FE.
LC838:  bcs +                           ;
LC83A:  sta ObjAction,x                 ;Clear RAM $300 thru $3FE.
LC83D:* inx                             ;
LC83E:  bne ---                         ;Loop until all required RAM is cleared.

LC840:  jsr ScreenOff                   ;($C439)Turn off Background and visibility.
LC843:  jsr ClearNameTables             ;($C158)Clear screen data.
LC846:  jsr EraseAllSprites             ;($C1A3)Erase all sprites from sprite RAM.
LC849:  jsr DestroyEnemies              ;($C8BB)

        stx DoorOnNameTable3            ;Clear data about doors on the name tables.
        stx DoorOnNameTable0            ;
        inx                             ;X=1.
        stx SpareMem30                  ;Not accessed by game.
        inx                             ;X=2.
LC854:  stx ScrollDir                   ;Set initial scroll direction as left.

        lda $95D7                       ;Get Samus start x pos on map.
        sta MapPosX                     ;
        lda $95D8                       ;Get Samus start y pos on map.
        sta MapPosY                     ;

LC860:  lda $95DA       ; Get ??? Something to do with palette switch
        sta PalToggle
        lda #$FF
        sta RoomNumber                  ;Room number = $FF(undefined room).
LC869:  jsr CopyPtrs    ; copy pointers from ROM to RAM 
LC86C:  jsr GetRoomNum                  ;($E720)Put room number at current map pos in $5A.
*       jsr SetupRoom                   ;($EA2B)
        ldy RoomNumber  ; load room number
        iny
        bne -

        ldy CartRAMPtr+1
        sty $01
        ldy CartRAMPtr
        sty $00
        lda PPUCNT0ZP
        and #$FB        ; PPU increment = 1
        sta PPUCNT0ZP
        sta PPUControl0
        ldy PPUStatus   ; reset PPU addr flip/flop

; Copy room RAM #0 ($6000) to PPU Name Table #0 ($2000)

        ldy #$20
        sty PPUAddress
        ldy #$00
        sty PPUAddress
        ldx #$04        ; prepare to write 4 pages
*       lda ($00),y
        sta PPUIOReg
        iny
        bne -
        inc $01
        dex
        bne -

        stx $91
        inx          ; X = 1
        stx PalDataPending
        stx SpareMem30                  ;Not accessed by game.
        inc MainRoutine                 ;SamusInit is next routine to run.
        jmp ScreenOn

; CopyPtrs
; ========
; Copy 7 16-bit pointers from $959A thru $95A7 to $3B thru $48.

CopyPtrs:
        ldx #$0D
*       lda AreaPointers+2,x
        sta RoomPtrTable,x
        dex
        bpl -
        rts

; DestroyEnemies
; ==============

DestroyEnemies:
LC8BB:  lda #$00
        tax
*       cpx #$48
        bcs +
        sta $97,x
*       sta EnStatus,x
        pha
        pla
        inx
        bne --
        stx MetroidOnSamus              ;Samus had no Metroid stuck to her.
        jmp $95AB

; SamusInit
; =========
; Code that sets up Samus, when the game is first started.

SamusInit:
LC8D1:  lda #$08                        ;
LC8D3:  sta MainRoutine                 ;SamusIntro will be executed next frame.
LC8D5:  lda #$2C                        ;440 frames to fade in Samus(7.3 seconds).
LC8D7:  sta Timer3                      ;
LC8D9:  jsr IntroMusic                  ;($CBFD)Start the intro music.
LC8DC:  ldy #sa_FadeIn0                 ;
        sty ObjAction                   ;Set Samus status as fading onto screen.
        ldx #$00
        stx SamusBlink
        dex                             ;X = $FF
        stx $0728
        stx $0730
        stx $0732
        stx $0738
        stx EndTimerLo                  ;Set end timer bytes to #$FF as-->
        stx EndTimerHi                  ;escape timer not currently active.
        stx $8B
        stx $8E
        ldy #$27
        lda InArea
        and #$0F
        beq +                           ;Branch if Samus starting in Brinstar.
        lsr ScrollDir                   ;If not in Brinstar, change scroll direction from left-->
        ldy #$2F                        ;to down. and set PPU for horizontal mirroring.
*       sty MirrorCntrl                 ;
        sty MaxMissilePickup
        sty MaxEnergyPickup
        lda $95D9                       ;Samus' initial vertical position
        sta ObjectY                     ;
        lda #$80                        ;Samus' initial horizontal position
        sta ObjectX                     ;
        lda PPUCNT0ZP                   ;
        and #$01                        ;Set Samus' name table position to current name table-->
        sta ObjectHi                    ;active in PPU.
        lda #$00                        ;
        sta HealthLo                    ;Starting health is-->
        lda #$03                        ;set to 30 units.
        sta HealthHi                    ;
*       rts                             ;

;------------------------------------[ Main game engine ]--------------------------------------------

GameEngine:
LC92B:  jsr ScrollDoor                  ;($E1F1)Scroll doors, if needed. 2 routine calls scrolls-->
LC92E:  jsr ScrollDoor                  ;($E1F1)twice as fast as 1 routine call.

LC931:  lda NARPASSWORD                 ;
LC934:  beq +                           ;
LC936:  lda #$03                        ;The following code is only accessed if -->
LC938:  sta HealthHi                    ;NARPASSWORD has been entered at the -->
LC93B:  lda #$FF                        ;password screen. Gives you new health,-->
LC93D:  sta SamusGear                   ;missiles and every power-up every frame.
LC940:  lda #$05                        ;
LC942:  sta MissileCount                ;

LC945:* jsr UpdateWorld                 ;($CB29)Update Samus, enemies and room tiles.
LC948:  lda MiniBossKillDelay           ;
LC94B:  ora PowerUpDelay                ;Check if mini boss was just killed or powerup aquired.-->
LC94E:  beq +                           ;If not, branch.

LC950:  lda #$00                        ;
LC952:  sta MiniBossKillDelay           ;Reset delay indicators.
LC955:  sta PowerUpDelay                ;
LC958:  lda #$18                        ;Set timer for 240 frames(4 seconds).
LC95A:  ldx #$03                        ;GameEngine routine to run after delay expires
LC95C:  jsr SetTimer                    ;($C4AA)Set delay timer and game engine routine.

LC95F:* lda ObjAction                   ;Check is Samus is dead.
LC962:  cmp #sa_Dead2                   ;Is Samus dead?-->
LC964:  bne ---                         ;exit if not.
LC966:  lda AnimDelay                   ;Is Samus still exploding?-->
LC969:  bne ---                         ;Exit if still exploding.
LC96B:  jsr SilenceMusic                ;Turn off music.
LC96E:  lda MotherBrainStatus           ;
LC970:  cmp #$0A                        ;Is mother brain already dead? If so, branch.
LC972:  beq +                           ;
LC974:  lda #$04                        ;Set timer for 40 frames (.667 seconds).
LC976:  ldx #$04                        ;GameOver routine to run after delay expires.
LC978:  jmp SetTimer                    ;($C4AA)Set delay timer and run game over routine.

LC97B:* inc MainRoutine                 ;Next routine to run is GameOver.
LC97D:  rts                             ;

;----------------------------------------[ Update age ]----------------------------------------------

;This is the routine which keeps track of Samus' age. It is called in the
;NMI. Basically, this routine just increments a 24-bit variable every
;256th frame. (Except it's not really 24-bit, because the lowest age byte
;overflows at $D0.)

UpdateAge:
LC97E:  lda GameMode                    ;
LC980:  bne ++                          ;Exit if at title/password screen.
LC982:  lda MainRoutine                 ;
LC984:  cmp #$03                        ;Is game engine running?
LC986:  bne ++                          ;If not, don't update age.
LC988:  ldx FrameCount                  ;Only update age when FrameCount is zero-->
LC98A:  bne ++                          ;(which is approx. every 4.266666666667 seconds).
LC98C:  inc SamusAge,x                  ;Minor Age = Minor Age + 1.
LC98F:  lda SamusAge                    ;
LC992:  cmp #$D0                        ;Has Minor Age reached $D0?-->
LC994:  bcc ++                          ;If not, we're done.-->
LC996:  lda #$00                        ;Else reset minor age.
LC998:  sta SamusAge                    ;
LC99B:* cpx #$03                        ;
LC99D:  bcs +                           ;Loop to update middle age and possibly major age.
LC99F:  inx                             ;
LC9A0:  inc SamusAge,x                  ;
LC9A3:  beq -                           ;Branch if middle age overflowed, need to increment--> 
LC9A5:* rts                             ;major age too. Else exit.

;-------------------------------------------[ Game over ]--------------------------------------------

GameOver:
LC9A6:  lda #$1C                        ;GameOver is the next routine to run.
LC9A8:  sta TitleRoutine                ;
LC9AA:  lda #$01                        ;
LC9AC:  sta SwitchPending               ;Prepare to switch to title memory page.
LC9AE:  jmp ScreenOff                   ;($C439)Turn screen off.

;------------------------------------------[ Pause mode ]--------------------------------------------

PauseMode:
LC9B1:  lda Joy2Status                  ;Load buttons currently being pressed on joypad 2.
LC9B3:  and #$88                        ;
LC9B5:  eor #$88                        ;both A & UP pressed?-->
LC9B7:  bne Exit14                      ;Exit if not.
LC9B9:  ldy EndTimerHi                  ;
LC9BC:  iny                             ;Is escape timer active?-->
LC9BD:  bne Exit14                      ;Sorry, can't quit if this is during escape scence.
LC9BF:  sta GamePaused                  ;Clear pause game indicator.
LC9C1:  inc MainRoutine                 ;Display password is the next routine to run.

Exit14:
LC9C3:  rts                             ;Exit for routines above and below.

;------------------------------------------[ GoPassword ]--------------------------------------------

GoPassword:
LC9C4:  lda #$19                        ;DisplayPassword is next routine to run.
LC9C6:  sta TitleRoutine                ;
LC9C8:  lda #$01                        ;
LC9CA:  sta SwitchPending               ;Prepare to switch to intro memory page.
LC9CC:  lda NoiseSFXFlag                ;
LC9CF:  ora #$01                        ;Silence music.
LC9D1:  sta NoiseSFXFlag                ;
LC9D4:  jmp ScreenOff                   ;($C439)Turn off screen.

;-----------------------------------------[ Samus intro ]--------------------------------------------

SamusIntro:
LC9D7:  jsr EraseAllSprites             ;($C1A3)Clear all sprites off screen.
LC9DA:  ldy ObjAction                   ;Load Samus' fade in status.
LC9DD:  lda Timer3                      ;
LC9E0:  bne +                           ;Branch if Intro still playing.
        
;Fade in complete.
LC9E2:  sta ItemRoomMusicStatus         ;Make sure item room music is not playing.
LC9E4:  lda #sa_Begin                   ;Samus facing forward and can't be hurt.
LC9E6:  sta ObjAction                   ;
LC9E8:  jsr StartMusic                  ;($D92C)Start main music.
LC9EB:  jsr SelectSamusPal              ;($CB73)Select proper Samus palette.
LC9EE:  lda #$03                        ;
LC9F0:  sta MainRoutine                 ;Game engine will be called next frame.

;Still fading in.
LC9F2:* cmp #$1F                        ;When 310 frames left of intro, display Samus.
LC9F4:  bcs Exit14                      ;Branch if not time to start drawing Samus.
LC9F6:  cmp SamusFadeInTimeTbl-20,y     ;sa_FadeIn0 is beginning of table.
LC9F9:  bne +                           ;Every time Timer3 equals one of the entries in the table-->
LC9FB:  inc ObjAction                   ;below, change the palette used to color Samus.
LC9FE:  sty PalDataPending              ;
LCA00:* lda FrameCount                  ;Is game currently on an odd frame?-->
LCA02:  lsr                             ;If not, branch to exit.
LCA03:  bcc Exit14                      ;Only display Samus on odd frames [the blink effect].
LCA05:  lda #an_SamusFront              ;Samus front animation is animation to display.-->
LCA07:  jsr SetSamusAnim                ;($CF6B)while fading in.
LCA0A:  lda #$00                        ;
LCA0C:  sta SpritePagePos               ;Samus sprites start at Sprite00RAM.
LCA0E:  sta PageIndex                   ;Samus RAM is first set of RAM.
LCA10:  jmp AnimDrawObject              ;($DE47)Draw Samus on screen.

;The following table marks the time remaining in Timer3 when a palette change should occur during
;the Samus fade-in sequence. This creates the fade-in effect.

SamusFadeInTimeTbl:
LCA13:  .byte $1E,$14,$0B,$04,$FF

;---------------------------------[ Check if game engine running ]-----------------------------------

IsEngineRunning:
LCA18:  ldy MainRoutine                 ;If Samus is fading in or the wait timer is-->
LCA1A:  cpy #$07                        ;active, return from routine.
LCA1C:  beq +                           ;
LCA1E:  cpy #$03                        ;Is game engine running?
LCA20:  beq ++                          ;If yes, branch to SwitchBank.
LCA22:* rts                             ;Exit if can't switch bank.

;-----------------------------------------[ Switch bank ]--------------------------------------------

;Switch to appropriate area bank

SwitchBank:
LCA23:* sta InArea                      ;Save current area Samus is in.
LCA25:  and #$0F                        ;
LCA27:  tay                             ;Use 4 LSB to load switch pending offset from BankTable table.
LCA28:  lda BankTable,y                 ;Base is $CA30.
LCA2B:  sta SwitchPending               ;Store switch data.
LCA2D:  jmp CheckSwitch                 ;($C4DE)Switch lower 16KB to appropriate memory page.

;Table used by above subroutine.
;Each value is the area bank number plus one.

BankTable:
LCA30:  .byte $02                       ;Brinstar.
LCA31:  .byte $03                       ;Norfair.
LCA32:  .byte $05                       ;Kraid hideout.
LCA33:  .byte $04                       ;Tourian.
LCA34:  .byte $06                       ;Ridley hideout.

;----------------------------------[ Saved game routines (not used) ]--------------------------------

AccessSavedGame:
LCA35:  pha                             ;Save two copies of A. Why? Who knows. This code is-->
LCA36:  pha                             ;Never implemented. A contains data slot to work on.
LCA37:  jsr GetGameDataIndex            ;($CA96)Get index to this save game Samus data info.
LCA3A:  lda EraseGame                   ;
LCA3D:  bpl +                           ;Is MSB set? If so, erase saved game data. Else branch.
LCA3F:  and #$01                        ;
LCA41:  sta EraseGame                   ;Clear MSB so saved game data is not erased again.
LCA44:  jsr EraseAllGameData            ;($CAA1)Erase selected saved game data.
LCA47:  lda #$01                        ;Indicate this saved game has been erased.-->
LCA49:  sta $7800,y                     ;Saved game 0=$780C, saved game 1=$781C, saved game 2=$782C. 
LCA4C:* lda MainRoutine                 ;
LCA4E:  cmp #$01                        ;If initializing the area at the start of the game, branch-->
LCA50:  beq +++                         ;to load Samus' saved game info.

SaveGameData:
LCA52:  lda InArea                      ;Save game based on current area Samus is in. Don't know why.
LCA54:  jsr SavedDataBaseAddr           ;($CAC6)Find index to unique item history for this saved game.
LCA57:  ldy #$3F                        ;Prepare to save unique item history which is 64 bytes-->
LCA59:* lda NumberOfUniqueItems,y       ;in length.
LCA5C:  sta ($00),y                     ;Save unique item history in appropriate saved game slot.
LCA5E:  dey                             ;
LCA5F:  bpl -                           ;Loop until unique item history transfer complete.
LCA61:  ldy SamusDataIndex              ;Prepare to save Samus' data.
LCA64:  ldx #$00                        ;
LCA66:* lda SamusStat00,x               ;
LCA69:  sta SamusData,y                 ;Save Samus' data in appropriate saved game slot.
LCA6C:  iny                             ;
LCA6D:  inx                             ;
LCA6E:  cpx #$10                        ;
LCA70:  bne -                           ;Loop until Samus' data transfer complete.

LoadGameData:
LCA72:* pla                             ;Restore A to find appropriate saved game to load.
LCA73:  jsr SavedDataBaseAddr           ;($CAC6)Find index to unique item history for this saved game.
LCA76:  ldy #$3F                        ;Prepare to load unique item history which is 64 bytes-->
LCA78:* lda ($00),y                     ;in length.
LCA7A:  sta NumberOfUniqueItems,y       ;Loop until unique item history is loaded.
LCA7D:  dey                             ;
LCA7E:  bpl -                           ;
LCA80:  bmi +                           ;Branch always.
LCA82:  pha                             ;
LCA83:* ldy SamusDataIndex              ;Prepare to load Samus' data.
LCA86:  ldx #$00                        ;
LCA88:* lda SamusData,y                 ;
LCA8B:  sta SamusStat00,x               ;Load Samus' data from appropriate saved game slot.
LCA8E:  iny                             ;
LCA8F:  inx                             ;
LCA90:  cpx #$10                        ;
LCA92:  bne -                           ;Loop until Samus' data transfer complete.
LCA94:  pla                             ;
LCA95:  rts                             ;

GetGameDataIndex:
LCA96:  lda DataSlot                    ;
LCA99:  asl                             ;A contains the save game slot to work on (0 1 or 2).-->
LCA9A:  asl                             ;This number is transferred to the upper four bits to-->
LCA9B:  asl                             ;find the offset for Samus' data for this particular-->
LCA9C:  asl                             ;saved game (#$00, #$10 or #$20).
LCA9D:  sta SamusDataIndex              ;
LCAA0:  rts                             ;

EraseAllGameData:
LCAA1:  lda #$00                        ;Always start at saved game 0. Erase all 3 saved games.
LCAA3:  jsr SavedDataBaseAddr           ;($CAC6)Find index to unique item history for this saved game.
LCAA6:  inc $03                         ;Prepare to erase saved game info at $6A00 and above.
LCAA8:  ldy #$00                        ;Fill saved game data with #$00.
LCAAA:  tya                             ;
LCAAB:* sta ($00),y                     ;Erase unique item histories from $69B4 to $69FF. 
LCAAD:  cpy #$40                        ;
LCAAF:  bcs +                           ;IF 64 bytes alrady erased, no need to erase any more-->
LCAB1:  sta ($02),y                     ;in the $6A00 and above range.
LCAB3:* iny                             ;
LCAB4:  bne --                          ;Lop until all saved game data is erased.
LCAB6:  ldy SamusDataIndex              ;Load proper index to desired Samus data to erase.
LCAB9:  ldx #$00                        ;
LCABB:  txa                             ;
LCABC:* sta SamusData,y                 ;Erase Samus' data.
LCABF:  iny                             ;
LCAC0:  inx                             ;
LCAC1:  cpx #$0C                        ;
LCAC3:  bne -                           ;Loop until all data is erased.
LCAC5:  rts                             ;

;This routine finds the base address of the unique item history for the desired saved game (0, 1 or 2).
;The memory set aside for each unique item history is 64 bytes and occupies memory addresses $69B4 thru
;$6A73.

SavedDataBaseAddr:
LCAC6:  pha                             ;Save contents of A.
LCAC7:  lda DataSlot                    ;Load saved game data slot to load.
LCACA:  asl                             ;*2. Table values below are two bytes.
LCACB:  tax                             ;
LCACC:  lda SavedDataTable,x            ;
LCACF:  sta $00                         ;Load $0000 and $0002 with base addresses from-->
LCAD1:  sta $02                         ;table below($69B4).
LCAD3:  lda SavedDataTable+1,x          ;
LCAD6:  sta $01                         ;
LCAD8:  sta $03                         ;
LCADA:  pla                             ;Restore A.
LCADB:  and #$0F                        ;Discard upper four bits in A.
LCADD:  tax                             ;X used for counting loop.
LCADE:  beq +++                         ;Exit if at saved game 0.  No further calculations required.
LCAE0:* lda $00                         ;
LCAE2:  clc                             ;
LCAE3:  adc #$40                        ;
LCAE5:  sta $00                         ;Loop to add #$40 to base address of $69B4 in order to find-->
LCAE7:  bcc +                           ;the proper base address for this saved game data. (save-->
LCAE9:  inc $01                         ;slot 0 = $69B4, save slot 1 = $69F4, save slot 2 = $6A34).
LCAEB:* dex                             ;
LCAEC:  bne --                          ;
LCAEE:* rts                             ;

;Table used by above subroutine to find base address to load saved game data from. The slot 0
;starts at $69B4, slot 1 starts at $69F4 and slot 2 starts at $6A34.

SavedDataTable:
LCAEF:  .word ItmeHistory               ;($69B4)Base for save game slot 0.
LCAF1:  .word ItmeHistory               ;($69B4)Base for save game slot 1.
LCAF3:  .word ItmeHistory               ;($69B4)Base for save game slot 2.

;----------------------------------------[ Choose ending ]-------------------------------------------

;Determine what type of ending is to be shown, based on Samus' age.
ChooseEnding:
LCAF5:  ldy #$01                        ;
LCAF7:* lda SamusAge+2                  ;If SamusAge+2 anything but #$00, load worst-->
LCAFA:  bne +                           ;ending(more than 37 hours of gameplay).
LCAFC:  lda SamusAge+1                  ;
LCAFF:  cmp AgeTable-1,y                ;Loop four times to determine-->
LCB02:  bcs +                           ;ending type from table below.
LCB04:  iny                             ;
LCB05:  cpy #$05                        ;
LCB07:  bne -                           ;
LCB09:* sty EndingType                  ;Store the ending # (1..5), 5=best ending
LCB0C:  lda #$00                        ;
LCB0E:  cpy #$04                        ;Was the best or 2nd best ending achieved?
LCB10:  bcc +                           ;Branch if not (suit stays on)
LCB12:  lda #$01                        ;
LCB14:* sta JustInBailey                ;Suit OFF, baby!
LCB17:  rts                             ;

;Table used by above subroutine to determine ending type.
AgeTable:
LCB18:  .byte $7A                       ;Max. 37 hours
LCB19:  .byte $16                       ;Max. 6.7 hours
LCB1A:  .byte $0A                       ;Max. 3.0 hours
LCB1B:  .byte $04                       ;Best ending. Max. 1.2 hours

;--------------------------------[ Clear screen data (not used) ]------------------------------------

ClearScreenData:
LCB1C:  jsr ScreenOff                   ;($C439)Turn off screen.
LCB1F:  lda #$FF                        ;
LCB21:  sta $00                         ;Prepare to fill nametable with #$FF.
LCB23:  jsr ClearNameTable              ;($C175)Clear selected nametable.
LCD26:  jmp EraseAllSprites             ;($C1A3)Clear sprite data.

;----------------------------------------------------------------------------------------------------

; ===== THE REAL GUTS OF THE GAME ENGINE! =====

UpdateWorld:
LCB29:  ldx #$00                        ;Set start of sprite RAM to $0200.
LCB2B:  stx SpritePagePos               ;

LCB2D:  jsr UpdateEnemies               ;($F345)Display of enemies.
LCB30:  jsr UpdateProjectiles           ;($D4BF)Display of bullets/missiles/bombs.
LCB33:  jsr UpdateSamus                 ;($CC0D)Display/movement of Samus.
LCB36:  jsr AreaRoutine                 ;($95C3)Area specific routine.
LCB39:  jsr UpdateElevator              ;($D7B3)Display of elevators.
LCB3C:  jsr UpdateStatues               ;($D9D4)Display of Ridley & Kraid statues.
LCB3F:  jsr $FA9D       ; destruction of enemies
LCB42:  jsr LFC65       ; update of Mellow/Memu enemies
LCB45:  jsr LF93B
LCB48:  jsr LFBDD       ; destruction of green spinners
LCB4B:  jsr SamusEnterDoor              ;($8B13)Check if Samus entered a door.
LCB4E:  jsr $8B79       ; display of doors
LCB51:  jsr UpdateTiles ; tile de/regeneration
LCB54:  jsr LF034       ; Samus <--> enemies crash detection
LCB57:  jsr DisplayBar                  ;($E0C1)Display of status bar.
        jsr LFAF2
        jsr CheckMissileToggle
        jsr UpdateItems                 ;($DB37)Display of power-up items.
        jsr UpdateTourianItems          ;($FDE3)

;Clear remaining sprite RAM
        ldx SpritePagePos
        lda #$F4
*       sta Sprite00RAM,x
        jsr Xplus4       ; X = X + 4
        bne -
        rts

;------------------------------------[ Select Samus palette ]----------------------------------------

; Select the proper palette for Samus based on:
; - Is Samus wearing Varia (protective suit)?
; - Is Samus firing missiles or regular bullets?
; - Is Samus with or without suit?

SelectSamusPal:
LCB73:  tya                             ;
        pha                             ;Temp storage of Y on the stack.
        lda SamusGear
        asl
        asl
        asl                             ;CF contains Varia status (1 = Samus has it)
        lda MissileToggle               ;A = 1 if Samus is firing missiles, else 0
        rol                             ;Bit 0 of A = 1 if Samus is wearing Varia
        adc #$02
        ldy JustInBailey                ;In suit?-->
        beq +                           ;If so, Branch.
        clc
        adc #$17                        ;Add #$17 to the pal # to reach "no suit"-palettes.
*       sta PalDataPending              ;Palette will be written next NMI.
        pla                             ;
        tay                             ;Restore the contents of y.
        rts                             ;

;----------------------------------[ Initiate SFX and music routines ]-------------------------------

;Initiate sound effects.

SilenceMusic:                           ;The sound flags are stored in memory-->
LCB8E:  lda #$01                        ;starting at $0680. The following is a-->
LCB90:  bne SFX_SetX0                   ;list of sound effects played when the-->
                                        ;flags are set:
PauseMusic:                             ;
LCB92:  lda #$02                        ;$0680: These SFX use noise channel.
LCB94:  bne SFX_SetX0                   ;Bit 7 - No sound.
                                        ;Bit 6 - ScrewAttack.
SFX_SamusWalk:                          ;Bit 5 - MissileLaunch.
LCB96:  lda #$08                        ;Bit 4 - BombExplode.
LCB98:  bne SFX_SetX0                   ;Bit 3 - SamusWalk.
                                        ;Bit 2 - SpitFlame.
SFX_BombExplode:                        ;Bit 1 - No sound.
LCB9A:  lda #$10                        ;Bit 0 - No sound.
LCB9C:  bne SFX_SetX0                   ;
                                        ;$0681: These SFX use sq1 channel.
SFX_MissileLaunch:                      ;Bit 7 - MissilePickup.
LCB9E:  lda #$20                        ;Bit 6 - EnergyPickup.
                                        ;Bit 5 - Metal.
SFX_SetX0:                              ;Bit 4 - BulletFire.
LCBA0:  ldx #$00                        ;Bit 3 - OutOfHole.
LCBA2:  beq SFX_SetSoundFlag            ;Bit 2 - EnemyHit.
                                        ;Bit 1 - SamusJump.
SFX_OutOfHole:                          ;Bit 0 - WaveFire.
LCBA4:  lda #$08                        ;
LCBA6:  bne SFX_SetX1                   ;$0682: Not used.
                                        ;
SFX_BombLaunch:                         ;$0683: These SFX use tri channel.
LCBA8:  lda #$01                        ;Bit 7 - SamusDie.
LCBAA:  bne SFX_SetX3                   ;Bit 6 - DoorOpenClose.
                                        ;Bit 5 - MetroidHit.
SFX_SamusJump:                          ;Bit 4 - StatueRaise.
LCBAC:  lda #$02                        ;Bit 3 - Beep.
LCBAE:  bne SFX_SetX1                   ;Bit 2 - BigEnemyHit.
                                        ;Bit 1 - SamusBall.
SFX_EnemyHit:                           ;Bit 0 - BombLaunch.
LCBB0:  lda #$04                        ;
LCBB2:  bne SFX_SetX1                   ;$0684: These SFX use multi channels.
                                        ;Bit 7 - FadeInMusic            (music).
SFX_BulletFire:                         ;Bit 6 - PowerUpMusic           (music).
LCBB4:  lda #$10                        ;Bit 5 - EndMusic  (Page 0 only)(music).
LCBB6:  bne SFX_SetX1                   ;Bit 4 - IntroMusic(Page 0 only)(music).
                                        ;Bit 3 - not used               (SFX).
SFX_Metal:                              ;Bit 2 - SamusHit               (SFX).
LCBB8:  lda #$20                        ;Bit 1 - BossHit                (SFX).
LCBBA:  bne SFX_SetX1                   ;Bit 0 - IncorrectPassword      (SFX).
                                        ;
SFX_EnergyPickup:                       ;$0685: Music flags. The music flags start different-->
LCBBC:  lda #$40                        ;music depending on what memory page is loaded. The-->
LCBBD:  bne SFX_SetX1                   ;following lists what bits start what music for each-->
                                        ;memory page.
SFX_MissilePickup:                      ;
LCBC0:  lda #$80                        ;Page 0: Intro/ending.
                                        ;Bit 7 - Not used.
SFX_SetX1:                              ;Bit 6 - TourianMusic.
LCBC2:  ldx #$01                        ;Bit 5 - ItemRoomMusic.
LCBC4:  bne SFX_SetSoundFlag            ;Bit 4 - Not used.
                                        ;Bit 3 - Not used.
SFX_WaveFire:                           ;Bit 2 - Not used.
LCBC6:  lda #$01                        ;Bit 1 - Not used.
LCBC8:  bne SFX_SetX1                   ;Bit 0 - Not used.
                                        ;
SFX_ScrewAttack:                        ;Page 1: Brinstar.
LCBCA:  lda #$40                        ;Bit 7 - Not used.
LCBCC:  bne SFX_SetX0                   ;Bit 6 - TourianMusic.
                                        ;Bit 5 - ItemRoomMusic.
SFX_BigEnemyHit:                        ;Bit 4 - Not used.
LCBCE:  lda #$04                        ;Bit 3 - Not used.
LCBD0:  bne SFX_SetX3                   ;Bit 2 - Not used.
                                        ;Bit 1 - Not used.
SFX_MetroidHit:                         ;Bit 0 - BrinstarMusic.
LCBD2:  lda #$20                        ;
LCBD4:  bne SFX_SetX3                   ;Page 2: Norfair.
                                        ;Bit 7 - Not used.
SFX_BossHit:                            ;Bit 6 - TourianMusic.
LCBD6:  lda #$02                        ;Bit 5 - ItemRoomMusic.
LCBD8:  bne SFX_SetX4                   ;Bit 4 - Not used.
                                        ;Bit 3 - NorfairMusic.
SFX_Door:                               ;Bit 2 - Not used.
LCBDA:  lda #$40                        ;Bit 1 - Not used.
LCBDC:  bne SFX_SetX3                   ;Bit 0 - Not used.
                                        ;
SFX_SamusHit:                           ;Page 3: Tourian.
LCBDE:  lda #$04                        ;Bit 7 - Not used.
LCBE0:  bne SFX_SetX4                   ;Bit 6 - TourianMusic
                                        ;Bit 5 - ItemRoomMusic.
SFX_SamusDie:                           ;Bit 4 - Not used.
LCBE2:  lda #$80                        ;Bit 3 - Not used.
LCBE4:  bne SFX_SetX3                   ;Bit 2 - EscapeMusic.
                                        ;Bit 1 - MotherBrainMusic
SFX_SetX2:                              ;Bit 0 - Not used.
LCBE6:  ldx #$02                        ;
                                        ;Page 4: Kraid.
SFX_SetSoundFlag:                       ;Bit 7 - RidleyAreaMusic.
LCBE8:  ora $0680,x                     ;Bit 6 - TourianMusic.
LCBEB:  sta $0680,x                     ;Bit 5 - ItemRoomMusic.
LCBEE:  rts                             ;Bit 4 - KraidAreaMusic.
                                        ;Bit 3 - Not used.
SFX_SamusBall:                          ;Bit 2 - Not used.
LCBEF:  lda #$02                        ;Bit 1 - Not used.
LCBF1:  bne SFX_SetX3                   ;Bit 0 - Not used.
                                        ;
SFX_Beep:                               ;Page 5: Ridley.
LCBF3:  lda #$08                        ;Bit 7 - RidleyAreaMusic.
                                        ;Bit 6 - TourianMusic.
SFX_SetX3:                              ;Bit 5 - ItemRoomMusic.
LCBF5:  ldx #$03                        ;Bit 4 - KraidAreaMusic.
LCBF7:  bne SFX_SetSoundFlag            ;Bit 3 - Not used.
                                        ;Bit 2 - Not used.
;Initiate music                         ;Bit 1 - Not used.
                                        ;Bit 0 - Not used.
PowerUpMusic:                           ;
LCBF9:  lda #$40                        ;
LCBFB:  bne SFX_SetX4                   ;
                                        ;
IntroMusic:                             ;
LCBFD:  lda #$80                        ;
                                        ;
SFX_SetX4:                              ;
LCBFF:  ldx #$04                        ;
LCC01:  bne SFX_SetSoundFlag            ;
                                        ;
MotherBrainMusic:                       ;
LCC03:  lda #$02                        ;
LCC05:  bne SFX_SetX5                   ;
                                        ;
TourianMusic:                           ;
LCC07:  lda #$40                        ;
                                        ;
SFX_SetX5:                              ;
LCC09:  ldx #$05                        ;
LCC0B:  bne SFX_SetSoundFlag            ;

;--------------------------------------[ Update Samus ]----------------------------------------------

UpdateSamus:
LCC0D:  ldx #$00                        ;Samus data is located at index #$00.
LCC0F:  stx PageIndex                   ;
LCC11:  inx                             ;x=1.
LCC12:  stx IsSamus                     ;Indicate Samus is the object being updated.
LCC14:  jsr GoSamusHandler              ;($CC1A)Find proper Samus handler routine.
LCC17:  dec IsSamus                     ;Update of Samus complete.
LCC19:  rts                             ;

GoSamusHandler:
LCC1A:  lda ObjAction                   ;
LCC1D:  bmi SamusStand                  ;Branch if Samus is standing.
LCC1F:  jsr ChooseRoutine               ;($C27C)Goto proper Samus handler routine.

;Pointer table for Samus' action handlers.

LCC22:  .word SamusStand                ;($CC36)Standing.
LCC24:  .word SamusRun                  ;($CCC2)Running.
LCC26:  .word SamusJump                 ;($D002)Jumping.
LCC28:  .word SamusRoll                 ;($D0E1)Rolling.
LCC2A:  .word SamusPntUp                ;($D198)Pointing up.
LCC2C:  .word SamusDoor                 ;($D3A8)Inside door while screen scrolling.
LCC2E:  .word SamusJump                 ;($D002)Jumping while pointing up.
LCC30:  .word SamusDead                 ;($D41A)Dead.
LCC32:  .word SamusDead2                ;($D41F)More dead.
LCC34:  .word SamusElevator             ;($D423)Samus on elevator.

;---------------------------------------[ Samus standing ]-------------------------------------------

SamusStand:
LCC36:  lda Joy1Status                  ;Status of joypad 1.
LCC38:  and #$CF                        ;Remove SELECT & START status bits.
LCC3A:  beq +                           ;Branch if no buttons pressed.
LCC3C:  jsr ClearHorzMvmtAnimData       ;($CF5D)Set no horiontal movement and single frame animation.
LCC3F:  lda Joy1Status                  ;
LCC41:* and #$07                        ;Keep status of DOWN/LEFT/RIGHT.
LCC43:  bne +                           ;Branch if any are pressed.
LCC45:  lda Joy1Change                  ;
LCC47:  and #$08                        ;Check if UP was pressed last frame.-->
LCC49:  beq +++                         ;If not, branch.
LCC4B:* jsr BitScan                     ;($E1E1)Find which directional button is pressed.
LCC4E:  cmp #$02                        ;Is down pressed?-->
LCC50:  bcs +                           ;If so, branch.
LCC52:  sta SamusDir                    ;1=left, 0=right.
LCC54:* tax                             ;
LCC55:  lda ActionTable,x               ;Load proper Samus status from table below.
LCC58:  sta ObjAction                   ;Save Samus status.
LCC5B:* lda Joy1Change                  ;
LCC5D:  ora Joy1Retrig                  ;Check if fire was just pressed or needs to retrigger.
LCC5F:  asl                             ;
LCC60:  bpl +                           ;Branch if FIRE not pressed.
LCC62:  jsr FireWeapon                  ;($D1EE)Shoot left/right.
LCC65:* bit Joy1Change                  ;Check if jump was just pressed.
LCC67:  bpl +                           ;Branch if JUMP not pressed.
LCC69:  lda #sa_Jump                    ;
LCC6B:  sta ObjAction                   ;Set Samus status as jumping.
LCC6E:* lda #$04                        ;Prepare to set animation delay to 4 frames.
LCC70:  jsr SetSamusData                ;($CD6D)Set Samus control data and animation.
LCC73:  lda ObjAction                   ;
LCC76:  cmp #sa_Door                    ;Is Samus inside a door, dead or pointing up and jumping?-->
LCC78:  bcs +                           ;If so, branch to exit.
LCC7A:  jsr ChooseRoutine               ;Select routine below.

;Pointer table to code.

LCC7D:  .word ExitSub                   ;($C45C)Rts.
LCC7F:  .word SetSamusRun               ;($CC98)Samus is running.
LCC81:  .word SetSamusJump              ;($CFC3)Samus is jumping.
LCC83:  .word SetSamusRoll              ;($D0B5)Samus is in a ball.
LCC85:  .word SetSamusPntUp             ;($CF77)Samus is pointing up.

;Table used by above subroutine.

ActionTable:
LCC87:  .byte sa_Run                    ;Run right.
LCC88:  .byte sa_Run                    ;Run left.
LCC89:  .byte sa_Roll
LCC8A:  .byte sa_PntUp

;----------------------------------------------------------------------------------------------------

SetSamusExplode:
LCC8B:  lda #$50
        sta SamusJumpDsplcmnt
        lda #an_Explode
        jsr SetSamusAnim
        sta ObjectCounter
*       rts

SetSamusRun:
LCC98:  lda #$09
        sta WalkSoundDelay
        ldx #$00
        lda AnimResetIndex
        cmp #an_SamusStand
        beq +
        inx
        cmp #$27
        beq +
        lda #$04
        jsr SetSamusNextAnim
*       lda RunAnimationTbl,x
        sta AnimResetIndex
        ldx SamusDir
LCCB7:  lda RunAccelerationTbl,x
        sta SamusHorzAccel
        rts

RunAnimationTbl:
LCCBE:  .byte an_SamusRun
        .byte an_SamusRunPntUp

RunAccelerationTbl:
LCCC0:  .byte $30                       ;Accelerate right.
        .byte $D0                       ;Accelerate left.

; SamusRun
; ========

SamusRun:
LCCC2:  ldx SamusDir
        lda SamusGravity
        beq +++++++
        ldy SamusJumpDsplcmnt
        bit ObjVertSpeed
        bmi +
        cpy #$18
        bcs ++++
        lda #an_SamusJump
        sta AnimResetIndex
        bcc ++++          ; branch always
*       cpy #$18
        bcc +++
        lda AnimResetIndex
        cmp #an_SamusFireJump
        beq +
        lda #an_SamusSalto
        sta AnimResetIndex
*       cpy #$20
        bcc ++
        lda Joy1Status
        and #$08
        beq +
        lda #an_SamusJumpPntUp
        sta AnimResetIndex
*       bit Joy1Status
        bmi +
        jsr StopVertMovement            ;($D147)
*       lda #an_SamusRun
        cmp AnimResetIndex
        bne +
        lda #an_SamusJump
        sta AnimResetIndex
*       lda SamusInLava
        beq +
        lda Joy1Change
        bmi LCD40       ; branch if JUMP pressed
*       jsr LCF88
        jsr LD09C
        jsr LCF2E
        lda #$02
        bne SetSamusData       ; branch always
*       lda SamusOnElevator
        bne +
        jsr LCCB7
*       jsr LCDBF
        dec WalkSoundDelay  ; time to play walk sound?
        bne +          ; branch if not
        lda #$09
        sta WalkSoundDelay  ; # of frames till next walk sound trigger
        jsr SFX_SamusWalk
*       jsr LCF2E
        lda Joy1Change
        bpl +      ; branch if JUMP not pressed
LCD40:  jsr LCFC3
        lda #$12
        sta SamusHorzSpeedMax
        jmp LCD6B

*       ora Joy1Retrig
        asl
        bpl +      ; branch if FIRE not pressed
        jsr LCDD7
*       lda Joy1Status
        and #$03
        bne +
        jsr LCF55
        jmp LCD6B

*       jsr BitScan                     ;($E1E1)
        cmp SamusDir
        beq LCD6B
        sta SamusDir
        jsr LCC98
LCD6B:  lda #$03

;---------------------------------------[ Set Samus data ]-------------------------------------------

;The following function sets various animation and control data bytes for Samus.

SetSamusData:
LCD6D:  jsr UpdateObjAnim               ;($DC8F)Update animation if needed.
LCD70:  jsr IsScrewAttackActive         ;($CD9C)Check if screw attack active to change palette.
LCD73:  bcs +                           ;If screw attack not active, branch to skip palette change.
LCD75:  lda FrameCount                  ;
LCD77:  lsr                             ;
LCD78:  and #$03                        ;Every other frame, change Samus palette while screw-->
LCD7A:  ora #$A0                        ;Attack is active.
LCD7C:  sta ObjectCntrl                 ;
LCD7E:* jsr CheckHealthStatus           ;($CDFA)Check if Samus hit, blinking or Health low.
LCD81:  jsr LavaAndMoveCheck            ;($E269)Check if Samus is in lava or moving.
LCD84:  lda MetroidOnSamus              ;Is a Metroid stuck to Samus?-->
LCD86:  beq +                           ;If not, branch.
LCD88:  lda #$A1                        ;Metroid on Samus. Turn Samus blue.
LCD8A:  sta ObjectCntrl                 ;
LCD8C:* jsr SetmirrorCntrlBit           ;($CD92)Mirror Samus, if necessary.
LCD8F:  jmp DrawFrame                   ;($DE4A)Display Samus.

;---------------------------------[ Set mirror control bit ]-----------------------------------------

SetmirrorCntrlBit:
LCD92:  lda SamusDir                    ;Facing left=#$01, facing right=#$00.
LCD94:  jsr Amul16                      ;($C2C5)*16. Move bit 0 to bit 4 position.
LCD97:  ora ObjectCntrl                 ;
LCD99:  sta ObjectCntrl                 ;Use SamusDir bit to set mirror bit.
LCD9B:  rts                             ;

;------------------------------[ Check if screw attack is active ]-----------------------------------

IsScrewAttackActive:
LCD9C:  sec                             ;Assume screw attack is not active.
LCD9D:  ldy ObjAction                   ;
LCDA0:  dey                             ;Is Samus running?-->
LCDA1:  bne ++                          ;If not, branch to exit.
LCDA3:  lda SamusGear                   ;
LCDA6:  and #gr_SCREWATTACK             ;Does Samus have screw attack?-->
LCDA8:  beq ++                          ;If not, branch to exit.
LCDAA:  lda AnimResetIndex              ;
LCDAD:  cmp #an_SamusSalto              ;Is Samus summersaulting?-->
LCDAF:  beq +                           ;If so, branch to clear carry(screw attack active).
LCDB1:  cmp #an_SamusJump               ;
LCDB3:  sec                             ;Is Samus jumping?-->
LCDB4:  bne ++                          ;If not, branch to exit.
LCDB6:  bit ObjVertSpeed                ;If Samus is jumping and still moving upwards, screw--> 
LCDB9:  bpl ++                          ;attack is active.
LCDBB:* cmp AnimIndex                   ;Screw attack will still be active if not spinning, but-->
LCDBE:* rts                             ;jumping while running and still moving upwards.

;----------------------------------------------------------------------------------------------------

LCDBF:  lda Joy1Status
        and #$08
        lsr
        lsr
        lsr
        tax
        lda LCCBE,x
        cmp AnimResetIndex
        beq -
        jsr SetSamusAnim
        pla
        pla
        jmp LCD6B

LCDD7:  jsr FireWeapon                  ;($D1EE)Shoot left/right.
        lda Joy1Status
        and #$08
        bne +
        lda #an_SamusFireRun
        sta AnimIndex
        rts

*       lda AnimIndex
        sec
        sbc AnimResetIndex
        and #$03
        tax
        lda Table05,x
        jmp SetSamusNextAnim

; Table used by above subroutine

Table05:
        .byte $3F
        .byte $3B
        .byte $3D
        .byte $3F

CheckHealthStatus:
LCDFA:  lda SamusHit                    ;
        and #$20                        ;Has Samus been hit?-->
        beq +++                         ;If not, branch to check if still blinking from recent hit.
        lda #$32                        ;
        sta SamusBlink                  ;Samus has been hit. Set blink for 32 frames.
        lda #$FF
        sta DamagePushDirection
        lda $73
        sta $77
        beq ++
        bpl +
        jsr SFX_SamusHit
*       lda SamusHit
        and #$08
        lsr
        lsr
        lsr
        sta DamagePushDirection
*       lda #$FD
        sta ObjVertSpeed
        lda #$38                        ;Samus is hit. Store Samus hit gravity.
        sta SamusGravity                ;
        jsr IsSamusDead
        bne +
        jmp CheckHealthBeep

*       lda SamusBlink
        beq CheckHealthBeep
        dec SamusBlink
        ldx DamagePushDirection
        inx
        beq +++
        jsr Adiv16       ; / 16
        cmp #$03
        bcs +
        ldy SamusHorzAccel
        bne +++
        jsr LCF4E
*       dex
        bne +
        jsr TwosCompliment              ;($C3D4)
*       sta ObjHorzSpeed
*       lda $77
        bpl CheckHealthBeep
        lda FrameCount
        and #$01
        bne CheckHealthBeep
        tay
        sty AnimDelay
        ldy #$F7
        sty AnimFrame

CheckHealthBeep:
        ldy HealthHi
        dey
        bmi +
        bne ++
        lda HealthLo
        cmp #$70
        bcs ++
; health < 17
*       lda FrameCount
        and #$0F
        bne +                           ;Only beep every 16th frame.
        jsr SFX_Beep
*       lda #$00
        sta SamusHit
LCE83:  rts

;----------------------------------------[ Is Samus dead ]-------------------------------------------

IsSamusDead:
LCE84:  lda ObjAction                   ;
LCE87:  cmp #sa_Dead                    ;
LCE89:  beq Exit3                       ;Samus is dead. Zero flag is set.
LCE8B:  cmp #sa_Dead2                   ;
LCE8D:  beq Exit3                       ;
LCE8F:  cmp #$FF                        ;Samus not dead. Clear zero flag.

Exit3:  
LCE91:  rts                             ;Exit for routines above and below.

;----------------------------------------[ Subtract health ]-----------------------------------------

SubtractHealth:
LCE92:  lda HealthLoChange              ;Check to see if health needs to be changed.-->
LCE94:  ora HealthHiChange              ;If not, branch to exit.
LCE96:  beq Exit3                       ;
LCE98:  jsr IsSamusDead                 ;($CE84)Check if Samus is already dead.
LCE9B:  beq ClearDamage                 ;Samus is dead. Branch to clear damage values.
LCE9D:  ldy EndTimerHi                  ;If end escape timer is running, Samus cannot be hurt.
LCEA0:  iny                             ;
LCEA1:  beq +                           ;Branch if end escape timer not active.

ClearDamage:
LCEA3:  jmp ClearHealthChange           ;($F323)Clear health change values.

LCEA6:* lda MotherBrainStatus           ;If mother brain is in the process of dying, receive-->
LCEA8:  cmp #$03                        ;no damage.
LCEAA:  bcs ClearDamage                 ;

LCEAC:  lda SamusGear                   ;
LCEAF:  and #gr_VARIA                   ;Check is Samus has Varia.
LCEB1:  beq +                           ;
LCEB3:  lsr HealthLoChange              ;If Samus has Varia, divide damage by 2.
LCEB5:  lsr HealthHiChange              ;
LCEB7:  bcc +                           ;If HealthHi moved a bit into the carry flag while-->
LCEB9:  lda #$4F                        ;dividing, add #$4F to HealthLo for proper-->
LCEBB:  adc HealthLoChange              ;division results.
LCEBD:  sta HealthLoChange              ;

LCEBF:* lda HealthLo                    ;Prepare to subtract from HealthLo.
LCEC2:  sta $03                         ;
LCEC4:  lda HealthLoChange              ;Amount to subtract from HealthLo.
LCEC6:  sec                             ;
LCEC7:  jsr Base10Subtract              ;($C3FB)Perform base 10 subtraction.
LCECA:  sta HealthLo                    ;Save results.

LCECD:   lda HealthHi                   ;Prepare to subtract from HealthHi.
LCED0:  sta $03                         ;
LCED2:  lda HealthHiChange              ;Amount to subtract from HealthHi.
LCED4:  jsr Base10Subtract              ;($C3FB)Perform base 10 subtraction.
LCED7:  sta HealthHi                    ;Save Results.

LCEDA:  lda HealthLo                    ;
LCEDD:  and #$F0                        ;Is Samus health at 0?  If so, branch to-->
LCEDF:  ora HealthHi                    ;begin death routine.
LCEE2:  beq +                           ;
LCEE4:  bcs ++                          ;Samus not dead. Branch to exit.

LCEE6:* lda #$00                        ;Samus is dead.
LCEE8:  sta HealthLo                    ;
LCEEB:  sta HealthHi                    ;Set health to #$00.
LCEEE:  lda #sa_Dead                    ;
LCEF0:  sta ObjAction                   ;Death handler.
LCEF3:  jsr SFX_SamusDie                ;($CBE2)Start Samus die SFX.
LCEF6:  jmp SetSamusExplode             ;($CC8B)Set Samus exlpode routine.

;----------------------------------------[ Add health ]----------------------------------------------

AddHealth:
LCEF9:  lda HealthLo                    ;Prepare to add to HealthLo.
LCEFC:  sta $03                         ;
LCEFE:  lda HealthLoChange              ;Amount to add to HealthLo.
LCF00:  clc                             ;
LCF01:  jsr Base10Add                   ;($C3DA)Perform base 10 addition.
LCF04:  sta HealthLo                    ;Save results.

LCF07:  lda HealthHi                    ;Prepare to add to HealthHi.
LCF0A:  sta $03                         ;
LCF0C:  lda HealthHiChange              ;Amount to add to HealthHi.
LCF0E:  jsr Base10Add                   ;($C3DA)Perform base 10 addition.
LCF11:  sta HealthHi                    ;Save results.

LCF14:  lda TankCount                   ;
LCF17:  jsr Amul16                      ;($C2C5)*16. Move tank count to upper 4 bits.
LCF1A:  ora #$0F                        ;Set lower 4 bits.
LCF1C:  cmp HealthHi                    ;
LCF1F:  bcs +                           ;Is life less than max? if so, branch.
LCF21:  and #$F9                        ;Life is more than max amount. 
LCF23:  sta HealthHi                    ;
LCF26:  lda #$99                        ;Set life to max amount.
LCF28:  sta HealthLo                    ;
LCF2B:* jmp ClearHealthChange           ;($F323)

;----------------------------------------------------------------------------------------------------

LCF2E:  lda SamusHit
LCF31:  lsr
        and #$02
        beq +++
        bcs +
        lda SamusHorzAccel
        bmi +++
        bpl ++
*       lda SamusHorzAccel
        bmi +
        bne ++
*       jsr TwosCompliment              ;($C3D4)
        sta SamusHorzAccel

ClearHorzMvmntData:
LCF4C:  ldy #$00                        ;
LCF4E:  sty ObjHorzSpeed                ;Set Samus Horizontal speed and horizontal-->
        sty HorzCntrLinear              ;linear counter to #$00.
*       rts                             ;

StopHorzMovement:
LCF55:  lda SamusHorzAccel              ;Is Samus moving horizontally?-->
        bne ClearHorzMvmtAnimData       ;If so, branch to stop movement.
        jsr SFX_SamusWalk               ;($CB96)Play walk SFX.

ClearHorzMvmtAnimData:
LCF5D:  jsr NoHorzMoveNoDelay           ;($CF81)Clear horizontal movement and animation delay data.
        sty ObjAction                   ;Samus is standing.
        lda Joy1Status                  ;
        and #$08                        ;Is The up button being pressed?-->
        bne +                           ;If so, branch.
        lda #an_SamusStand              ;Set Samus animation for standing.

SetSamusAnim:
LCF6B:  sta AnimResetIndex              ;Set new animation reset index.

SetSamusNextAnim:
        sta AnimIndex                   ;Set new animation data index.
        lda #$00                        ;
        sta AnimDelay                   ;New animation to take effect immediately.
        rts                             ;

SetSamusPntUp:
LCF77:* lda #sa_PntUp                   ;
        sta ObjAction                   ;Samus is pointing up.
        lda #an_SamusPntUp              ;
        jsr SetSamusAnim                ;($CF6B)Set new animation values.

NoHorzMoveNoDelay:
LCF81:  jsr ClearHorzData               ;($CFB7)Clear all horizontal movement data.
        sty AnimDelay                   ;Clear animation delay data.
        rts                             ;

LCF88:  lda Joy1Status
        and #$03
        beq +
        jsr BitScan                     ;($E1E1)
        tax
        jsr LCCB7
        lda SamusGravity
        bmi ++
        lda AnimResetIndex
        cmp #an_SamusSalto
        beq ++
        stx SamusDir
        lda Table06+1,x
        jmp SetSamusAnim

*       lda SamusGravity
        bmi +
        beq +
        lda AnimResetIndex
        cmp #an_SamusJump
        bne +

ClearHorzData:
LCFB7:  jsr ClearHorzMvmntData          ;($CF4C)Clear horizontal speed and linear counter.
        sty SamusHorzAccel              ;Clear horizontal acceleration data.
*       rts                             ;

LCFBE:  ldy #an_SamusJumpPntUp
        jmp +

SetSamusJump:
LCFC3:  ldy #an_SamusJump
*       sty AnimResetIndex
        dey
        sty AnimIndex
        lda #$04
        sta AnimDelay
        lda #$00
        sta SamusJumpDsplcmnt
        lda #$FC
        sta ObjVertSpeed
        ldx ObjAction
        dex
        bne +      ; branch if Samus is standing still
        lda SamusGear
        and #gr_SCREWATTACK
        beq +      ; branch if Samus doesn't have Screw Attack
        lda #$00
        sta $0686
        jsr SFX_ScrewAttack
*       jsr SFX_SamusJump
LCFF3:  ldy #$18        ; gravity (high value -> low jump)
        lda SamusGear
        and #gr_HIGHJUMP
        beq +      ; branch if Samus doesn't have High Jump
        ldy #$12        ; lower gravity value -> high jump!
*       sty SamusGravity
        rts

SamusJump:
        lda SamusJumpDsplcmnt
        bit ObjVertSpeed
        bpl +      ; branch if falling down
        cmp #$20
        bcc +      ; branch if jumped less than 32 pixels upwards
        bit Joy1Status
        bmi +      ; branch if JUMP button still pressed
        jsr StopVertMovement            ;($D147)Stop jump (start falling).
*       jsr LD055
        jsr LCF2E
        lda Joy1Status
        and #$08     ; UP pressed?
        beq +      ; branch if not
        lda #an_SamusJumpPntUp
        sta AnimResetIndex
        lda #sa_PntJump      ; "jumping & pointing up" handler
        sta ObjAction
*       jsr LD09C
        lda SamusInLava
        beq +
        lda Joy1Change
        bpl +      ; branch if JUMP not pressed
        jsr LCFC3
        jmp LCD6B

*       lda SamusGravity
        bne ++
        lda ObjAction
        cmp #sa_PntJump
        bne +
        jsr LCF77
        bne ++
*       jsr LCF55
*       lda #$03
        jmp SetSamusData                ;($CD6D)Set Samus control data and animation.

LD055:  ldx #$01
        ldy #$00
        lda Joy1Status
        lsr
        bcs +      ; branch if RIGHT pressed
        dex
        lsr
        bcc ++++       ; branch if LEFT not pressed
        dex
        iny
*       cpy SamusDir
        beq +++
        lda ObjAction
        cmp #sa_PntJump
        bne +
        lda AnimResetIndex
        cmp Table04,y
        bne ++
        lda Table04+1,y
        jmp ++

*       lda AnimResetIndex
        cmp Table06,y
        bne +
        lda Table06+1,y
*       jsr SetSamusAnim
        lda #$08
        sta AnimDelay
        sty SamusDir
*       stx ObjHorzSpeed
*       rts

; Table used by above subroutine

Table06:
        .byte $0C
        .byte $0C
        .byte $0C
Table04:
        .byte $35
        .byte $35
        .byte $35

LD09C:  lda Joy1Change
        ora Joy1Retrig
        asl
        bpl -      ; exit if FIRE not pressed
        lda AnimResetIndex
        cmp #an_SamusJumpPntUp
        bne +
        jmp LD275

*       jsr LD210
        lda #an_SamusFireJump
        jmp SetSamusAnim

SetSamusRoll:
LD0B5:  lda SamusGear
        and #gr_MARUMARI
        beq +      ; branch if Samus doesn't have Maru Mari
        lda SamusGravity
        bne +

;Turn Samus into ball
        ldx SamusDir
        lda #an_SamusRoll
        sta AnimResetIndex
        lda #an_SamusRunJump
        sta AnimIndex
        lda LCCC0,x
        sta SamusHorzAccel
        lda #$01
        sta $0686
        jmp SFX_SamusBall

*       lda #sa_Stand
        sta ObjAction
        rts

; SamusRoll
; =========

        SamusRoll:
        lda Joy1Change
        and #$08     ; UP pressed?
        bne +      ; branch if yes
        bit Joy1Change  ; JUMP pressed?
        bpl ++    ; branch if no
*       lda Joy1Status
        and #$04           ; DOWN pressed?
        bne +     ; branch if yes
;break out of "ball mode"
        lda ObjRadY
        clc
        adc #$08
        sta ObjRadY
        jsr CheckMoveUp
        bcc +     ; branch if not possible to stand up
        ldx #$00
        jsr LE8BE
        stx $05
        lda #$F5
        sta $04
        jsr LFD8F
        jsr LD638
        jsr LCF55
        dec AnimIndex
        jsr StopVertMovement            ;($D147)
        lda #$04
        jmp LD144

*       lda Joy1Change
        jsr BitScan                     ;($E1E1)
        cmp #$02
        bcs +
        sta SamusDir
        lda #an_SamusRoll
        jsr SetSamusAnim
*       ldx SamusDir
        jsr LCCB7
        jsr LCF2E
        jsr CheckBombLaunch
        lda Joy1Status
        and #$03
        bne +
        jsr LCFB7
*       lda #$02
LD144:  jmp SetSamusData                ;($CD6D)Set Samus control data and animation.

StopVertMovement:
LD147:  ldy #$00
        sty ObjVertSpeed
        sty VertCntrLinear
        rts

; CheckBombLaunch
; ===============
; This routine is called only when Samus is rolled into a ball.
; It does the following:
; - Checks if Samus has bombs
; - If so, checks if the FIRE button has been pressed
; - If so, checks if there are any object "slots" available
;   (only 3 bullets/bombs can be active at the same time)
; - If so, a bomb is launched.

        CheckBombLaunch:
        lda SamusGear
        lsr
        bcc ++    ; exit if Samus doesn't have Bombs
        lda Joy1Change
        ora Joy1Retrig
        asl             ; bit 7 = status of FIRE button
        bpl ++    ; exit if FIRE not pressed
        lda ObjVertSpeed
        ora SamusOnElevator
        bne ++
        ldx #$D0        ; try object slot D
        lda ObjAction,x
        beq +      ; launch bomb if slot available
        ldx #$E0        ; try object slot E
        lda ObjAction,x
        beq +      ; launch bomb if slot available
        ldx #$F0        ; try object slot F
        lda ObjAction,x
        bne ++    ; no bomb slots available, exit
; launch bomb... give it same coords as Samus
*       lda ObjectHi
        sta ObjectHi,x
        lda ObjectX
        sta ObjectX,x
        lda ObjectY
        clc
        adc #$04        ; 4 pixels further down than Samus' center
        sta ObjectY,x
        lda #wa_LayBomb
        sta ObjAction,x
        jsr SFX_BombLaunch
*       rts

        SamusPntUp:
        lda Joy1Status
        and #$08     ; UP still pressed?
        bne +      ; branch if yes
        lda #sa_Stand   ; stand handler
        sta ObjAction
*       lda Joy1Status
        and #$07        ; DOWN, LEFT, RIGHT pressed?
        beq ++    ; branch if no
        jsr BitScan                     ;($E1E1)
        cmp #$02
        bcs +
        sta SamusDir
*       tax
        lda Table07,x
        sta ObjAction
*       lda Joy1Change
        ora Joy1Retrig
        asl
        bpl +      ; branch if FIRE not pressed
        jsr FireWeapon                  ;($D1EE)Shoot up.
*       bit Joy1Change
        bpl +      ; branch if JUMP not pressed
        lda #sa_PntJump
        sta ObjAction
*       lda #$04
        jsr SetSamusData                ;($CD6D)Set Samus control data and animation.
        lda ObjAction
        jsr ChooseRoutine

; Pointer table to code

        .word $CF55
        .word $CC98
        .word ExitSub       ;($C45C)rts
        .word $D0B5
        .word ExitSub       ;($C45C)rts
        .word ExitSub       ;($C45C)rts
        .word $CFBE
        .word ExitSub       ;($C45C)rts
        .word ExitSub       ;($C45C)rts
        .word ExitSub       ;($C45C)rts

; Table used by above subroutine

Table07:
        .byte sa_Run
        .byte sa_Run
        .byte sa_Roll

FireWeapon:
LD1EE:  lda Joy1Status
        and #$08
        beq LD210
        jmp LD275

LD1F7:  ldy #$D0
*       lda ObjAction,y
        beq +
        jsr Yplus16
        bne -
        iny
        rts

*       sta $030A,y
        lda MissileToggle
        beq +
        cpy #$D0
*       rts

LD210:  lda MetroidOnSamus
        bne +
        jsr LD1F7
        bne +
        jsr LD2EB
        jsr LD359
        jsr LD38E
        lda #$0C
        sta $030F,y
        ldx SamusDir
        lda Table99,x   ; get bullet speed
        sta ObjHorzSpeed,y     ; -4 or 4, depending on Samus' direction
        lda #$00
        sta ObjVertSpeed,y
        lda #$01
        sta ObjectOnScreen,y
        jsr CheckMissileLaunch
        lda ObjAction,y
        asl
        ora SamusDir
        and #$03
        tax
        lda Table08,x
        sta $05
        lda #$FA
        sta $04
        jsr LD306
        lda SamusGear
        and #gr_LONGBEAM
        lsr
        lsr
        lsr
        ror
        ora $061F
        sta $061F
        ldx ObjAction,y
        dex
        bne +
        jsr SFX_BulletFire
*       ldy #$09
LD26B:  tya
        jmp SetSamusNextAnim

Table08:
        .byte $0C
        .byte $F4
        .byte $08
        .byte $F8

Table99:
        .byte $04
        .byte $FC

LD275:  lda MetroidOnSamus
        bne +
        jsr LD1F7
        bne +
        jsr LD2EB
        jsr LD38A
        jsr LD38E
        lda #$0C
        sta $030F,y
        lda #$FC
        sta ObjVertSpeed,y
        lda #$00
        sta ObjHorzSpeed,y
        lda #$01
        sta ObjectOnScreen,y
        jsr LD340
        ldx SamusDir
        lda Table09+4,x
        sta $05
        lda ObjAction,y
        and #$01
        tax
        lda Table09+6,x
        sta $04
        jsr LD306
        lda SamusGear
        and #gr_LONGBEAM
        lsr
        lsr
        lsr
        ror
        ora $061F
        sta $061F
        lda ObjAction,y
        cmp #$01
        bne +
        jsr SFX_BulletFire
*       ldx SamusDir
        ldy Table09,x
        lda SamusGravity
        beq +
        ldy Table09+2,x
*       lda ObjAction
        cmp #$01
        beq +
        jmp LD26B

; Table used by above subroutine

Table09:
        .byte $26
        .byte $26
        .byte $34
        .byte $34
        .byte $01
        .byte $FF
        .byte $EC
        .byte $F0

LD2EB:  tya
        tax
        inc ObjAction,x
        lda #$02
        sta ObjRadY,y
        sta ObjRadX,y
        lda #an_Bullet

SetProjectileAnim:
LD2FA:  sta AnimResetIndex,x
        sta AnimIndex,x
        lda #$00
        sta AnimDelay,x
*       rts

LD306:  ldx #$00
        jsr LE8BE
        tya
        tax
        jsr LFD8F
        txa
        tay
        jmp LD638

CheckMissileLaunch:
        lda MissileToggle
        beq Exit4       ; exit if Samus not in "missile fire" mode
        cpy #$D0
        bne Exit4
        ldx SamusDir
        lda MissileAnims,x
*       jsr SetBulletAnim
        jsr SFX_MissileLaunch
        lda #wa_Missile ; missile handler
        sta ObjAction,y
        lda #$FF
        sta $030F,y     ; # of frames projectile should last
        dec MissileCount
        bne Exit4       ; exit if not the last missile
; Samus has no more missiles left
        dec MissileToggle       ; put Samus in "regular fire" mode
        jmp SelectSamusPal      ; update Samus' palette to reflect this

MissileAnims:
        .byte an_MissileRight
        .byte an_MissileLeft

LD340:  lda MissileToggle
        beq Exit4
        cpy #$D0
        bne Exit4
        lda #$8F
        bne -

SetBulletAnim:
        sta AnimIndex,y
        sta AnimResetIndex,y
        lda #$00
        sta AnimDelay,y
Exit4:  rts

LD359:  lda SamusDir
*       sta $0502,y
        bit SamusGear
        bvc Exit4       ; branch if Samus doesn't have Wave Beam
        lda MissileToggle
        bne Exit4
        lda #$00
        sta $0501,y
        sta $0304,y
        tya
        jsr Adiv32      ; / 32
        lda #$00
        bcs +
        lda #$0C
*       sta $0500,y
        lda #wa_WaveBeam
        sta ObjAction,y
        lda #an_WaveBeam
        jsr SetBulletAnim
        jmp SFX_WaveFire

LD38A:  lda #$02
        bne --
LD38E:  lda MissileToggle
        bne Exit4
        lda SamusGear
        bpl Exit4       ; branch if Samus doesn't have Ice Beam
        lda #wa_IceBeam
        sta ObjAction,y
        lda $061F
        ora #$01
        sta $061F
        jmp SFX_BulletFire

; SamusDoor
; =========

SamusDoor:
        lda DoorStatus
        cmp #$05
        bcc +++++++
    ; move Samus out of door, how far depends on initial value of DoorDelay
        dec DoorDelay
        bne MoveOutDoor
    ; done moving
        asl
        bcc +
        lsr
        sta DoorStatus
        bne +++++++
*       jsr LD48C
        jsr LED65
        jsr $95AB
        lda ItemRoomMusicStatus
        beq ++
        pha
        jsr LD92C       ; start music
        pla
        bpl ++
        lda #$00
        sta ItemRoomMusicStatus
        beq ++
*       lda #$80
        sta ItemRoomMusicStatus
*       lda KraidRidleyPresent
        beq +
        jsr LCC07
        lda #$00
        sta KraidRidleyPresent
        beq --     ; branch always
*       lda SamusDoorData
        and #$0F
        sta ObjAction
        lda #$00
        sta SamusDoorData
        sta DoorStatus
        jsr StopVertMovement            ;($D147)

MoveOutDoor:
        lda SamusDoorDir
        beq ++    ; branch if door leads to the right
        ldy ObjectX
        bne +
        jsr ToggleSamusHi       ; toggle 9th bit of Samus' X coord
*       dec ObjectX
        jmp ++

*       inc ObjectX
        bne +
        jsr ToggleSamusHi       ; toggle 9th bit of Samus' X coord
*       jsr CheckHealthStatus           ;($CDFA)Check if Samus hit, blinking or Health low.
        jsr SetmirrorCntrlBit
        jmp DrawFrame       ; display Samus

SamusDead:
D41A:   lda #$01
        jmp SetSamusData                ;($CD6D)Set Samus control data and animation.

SamusDead2:
        dec AnimDelay
        rts

; SamusElevator
; =============

SamusElevator:
        lda ElevatorStatus
        cmp #$03
        beq +
        cmp #$08
        bne +++++++
*       lda $032F
        bmi +++
        lda ObjectY
        sec
        sbc ScrollY     ; A = Samus' Y position on the visual screen
        cmp #$84
        bcc +      ; if ScreenY < $84, don't scroll
        jsr ScrollDown  ; otherwise, attempt to scroll
*       ldy ObjectY
        cpy #239        ; wrap-around required?
        bne +
        jsr ToggleSamusHi       ; toggle 9th bit of Samus' Y coord
        ldy #$FF        ; ObjectY will now be 0
*       iny
        sty ObjectY
        jmp LD47E

*       lda ObjectY
        sec
        sbc ScrollY     ; A = Samus' Y position on the visual screen
        cmp #$64
        bcs +      ; if ScreenY >= $64, don't scroll
        jsr ScrollUp    ; otherwise, attempt to scroll
*       ldy ObjectY
        bne +      ; wraparound required? (branch if not)
        jsr ToggleSamusHi       ; toggle 9th bit of Samus' Y coord
        ldy #240        ; ObjectY will now be 239
*       dey
        sty ObjectY
        jmp LD47E

*       ldy #$00
        sty ObjVertSpeed
        cmp #$05
        beq +
        cmp #$07
        beq +
LD47E:  lda FrameCount
        lsr
        bcc ++
*       jsr SetmirrorCntrlBit           ;($CD92)Mirror Samus, if necessary.
        lda #$01
        jmp AnimDrawObject
*       rts

LD48C:  ldx #$60
        sec
*       jsr LD4B4
        txa
        sbc #$20
        tax
        bpl -
        jsr GetNameTable                ;($EB85)
        tay
        ldx #$18
*       jsr LD4A8
        txa
        sec
        sbc #$08
        tax
        bne -
LD4A8:  tya
        cmp $072C,x
        bne +
        lda #$FF
        sta $0728,x
*       rts

LD4B4:  lda $0405,x
LD4B7:  and #$02
LD4B9:  bne +
LD4BB:  sta EnStatus,x
LD4BE:* rts

; UpdateProjectiles
; =================

UpdateProjectiles:
        ldx #$D0
jsr DoOneProjectile
        ldx #$E0
jsr DoOneProjectile
        ldx #$F0
DoOneProjectile:
        stx PageIndex
        lda ObjAction,x
LD4D0:  jsr ChooseRoutine

LD4D3:  .word ExitSub     ;($C45C) rts
LD4D5:  .word UpdateBullet ; regular beam
        .word UpdateWaveBullet      ; wave beam
        .word UpdateIceBullet       ; ice beam
        .word BulletExplode    ; bullet/missile explode
        .word $D65E       ; lay bomb
        .word $D670       ; lay bomb
        .word $D691       ; lay bomb
        .word $D65E       ; lay bomb
        .word $D670       ; bomb countdown
        .word $D691       ; bomb explode
        .word UpdateBullet  ; missile

UpdateBullet:
        lda #$01
        sta UpdatingProjectile
        jsr LD5FC
        jsr LD5DA
        jsr LD609
CheckBulletStat:
        ldx PageIndex
        bcc +
        lda SamusGear
        and #gr_LONGBEAM
        bne DrawBullet  ; branch if Samus has Long Beam
        dec $030F,x     ; decrement bullet timer
        bne DrawBullet
        lda #$00        ; timer hit 0, kill bullet
        sta ObjAction,x
        beq DrawBullet  ; branch always
*       lda ObjAction,x
        beq +
        jsr LD5E4
DrawBullet:
        lda #$01
        jsr AnimDrawObject
*       dec UpdatingProjectile
        rts

*       inc $0500,x
LD522:  inc $0500,x
        lda #$00
        sta $0501,x
        beq +      ; branch always

UpdateWaveBullet:
        lda #$01
        sta UpdatingProjectile
        jsr LD5FC
        jsr LD5DA
        lda $0502,x
        and #$FE
        tay
        lda Table0A,y
        sta $0A
        lda Table0A+1,y
        sta $0B
*       ldy $0500,x
        lda ($0A),y
        cmp #$FF
        bne +
        sta $0500,x
        jmp LD522

*       cmp $0501,x
        beq ---
        inc $0501,x
        iny
        lda ($0A),y
        jsr $8296
        ldx PageIndex
        sta ObjVertSpeed,x
        lda ($0A),y
        jsr $832F
        ldx PageIndex
        sta ObjHorzSpeed,x
        tay
        lda $0502,x
        lsr
        bcc +
        tya
        jsr TwosCompliment              ;($C3D4)
        sta ObjHorzSpeed,x
*       jsr LD609
        bcs +
        jsr LD624
*       jmp CheckBulletStat

Table0A:
        .word Table0C     ; pointer to table #1 below
        .word Table0D     ; pointer to table #2 below

; Table #1 (size: 25 bytes)

Table0C:
        .byte $01
        .byte $F3
        .byte $01
        .byte $D3
        .byte $01
        .byte $93
        .byte $01
        .byte $13
        .byte $01
        .byte $53
        .byte $01
        .byte $73
        .byte $01
        .byte $73
        .byte $01
        .byte $53
        .byte $01
        .byte $13
        .byte $01
        .byte $93
        .byte $01
        .byte $D3
        .byte $01
        .byte $F3
        .byte $FF

; Table #2 (size: 25 bytes)

Table0D:
        .byte $01
        .byte $B7
        .byte $01
        .byte $B5
        .byte $01
        .byte $B1
        .byte $01
        .byte $B9
        .byte $01
        .byte $BD
        .byte $01
        .byte $BF
        .byte $01
        .byte $BF
        .byte $01
        .byte $BD
        .byte $01
        .byte $B9
        .byte $01
        .byte $B1
        .byte $01
        .byte $B5
        .byte $01
        .byte $B7
        .byte $FF

; UpdateIceBullet
; ===============

        UpdateIceBullet:
        lda #$81
        sta ObjectCntrl
        jmp UpdateBullet

; BulletExplode
; =============
; bullet/missile explode

        BulletExplode:
        lda #$01
        sta UpdatingProjectile
        lda $0303,x
        sec
        sbc #$F7
        bne +
        sta ObjAction,x  ; kill bullet
*       jmp DrawBullet

LD5DA:  lda $030A,x
        beq Exit5
        lda #$00
        sta $030A,x
LD5E4:  lda #$1D
        ldy ObjAction,x
        cpy #wa_BulletExplode
        beq Exit5
        cpy #wa_Missile
        bne +
        lda #an_MissileExplode
*       jsr SetProjectileAnim
        lda #wa_BulletExplode
*       sta ObjAction,x
Exit5:  rts

LD5FC:  lda ObjectOnScreen,x
        lsr
        bcs Exit5
*       lda #$00
        beq --   ; branch always
*       jmp LE81E

; bullet <--> background crash detection

LD609:  jsr GetObjCoords
        ldy #$00
        lda ($04),y     ; get tile # that bullet touches
        cmp #$A0
        bcs LD624
        jsr $95C0
        cmp #$4E
        beq -
        jsr LD651
        bcc ++
        clc
        jmp IsBlastTile

LD624:  ldx PageIndex
        lda ObjHorzSpeed,x
        sta $05
        lda ObjVertSpeed,x
        sta $04
        jsr LE8BE
        jsr LFD8F
        bcc --
LD638:  lda $08
        sta ObjectY,x
        lda $09
        sta ObjectX,x
        lda $0B
        and #$01
        bpl +      ; branch always
        ToggleObjectHi:
        lda ObjectHi,x
        eor #$01
*       sta ObjectHi,x
*       rts

LD651:  ldy InArea
        cpy #$10
        beq +
        cmp #$70
        bcs ++
*       cmp #$80
*       rts

LD65E:  lda #an_BombTick
        jsr SetProjectileAnim
        lda #$18        ; fuse length :-)
        sta $030F,x
        inc ObjAction,x       ; bomb update handler
        DrawBomb:
        lda #$03
        jmp AnimDrawObject

LD670:  lda FrameCount
        lsr
        bcc ++    ; only update counter on odd frames
        dec $030F,x
        bne ++
        lda #$37
        ldy ObjAction,x
        cpy #$09
        bne +
        lda #an_BombExplode
*       jsr SetProjectileAnim
        inc ObjAction,x
        jsr SFX_BombExplode
*       jmp DrawBomb

LD691:  inc $030F,x
        jsr LD6A7
        ldx PageIndex
        lda $0303,x
        sec
        sbc #$F7
        bne +
        sta ObjAction,x     ; kill bomb
*       jmp DrawBomb

LD6A7:  jsr GetObjCoords
        lda $04
        sta $0A
        lda $05
        sta $0B
        ldx PageIndex
        ldy $030F,x
        dey
        beq ++
        dey
        bne +++
        lda #$40
        jsr LD78B
        txa
        bne +
        lda $04
        and #$20
        beq Exit6
*       lda $05
        and #$03
        cmp #$03
        bne +
        lda $04
        cmp #$C0
        bcc +
        lda ScrollDir
        and #$02
        bne Exit6
        lda #$80
        jsr LD78B
*       jsr LD76A
Exit6:  rts

*       dey
        bne +++
        lda #$40
        jsr LD77F
        txa
        bne +
        lda $04
        and #$20
        bne Exit6
*       lda $05
        and #$03
        cmp #$03
        bne +
        lda $04
        cmp #$C0
        bcc +
        lda ScrollDir
        and #$02
        bne Exit6
        lda #$80
        jsr LD77F
*       jmp LD76A

*       dey
        bne +++
        lda #$02
        jsr LD78B
        txa
        bne +
        lda $04
        lsr
        bcc Exit7
*       lda $04
        and #$1F
        cmp #$1E
        bcc +
        lda ScrollDir
        and #$02
        beq Exit7
        lda #$1E
        jsr LD77F
        lda $05
        eor #$04
        sta $05
*       jmp LD76A

*       dey
        bne Exit7
        lda #$02
        jsr LD77F
        txa
        bne +
        lda $04
        lsr
        bcs Exit7
*       lda $04
        and #$1F
        cmp #$02
        bcs LD76A
        lda ScrollDir
        and #$02
        beq Exit7
        lda #$1E
        jsr LD78B
        lda $05
        eor #$04
        sta $05
LD76A:  txa
        pha
        ldy #$00
        lda ($04),y
        jsr LD651
        bcc +
        cmp #$A0
        bcs +
        jsr LE9C2
*       pla
        tax
Exit7:  rts

LD77F:  clc
        adc $0A
        sta $04
        lda $0B
        adc #$00
        jmp LD798

LD78B:  sta $00
        lda $0A
        sec
        sbc $00
        sta $04
        lda $0B
        sbc #$00
LD798:  and #$07
        ora #$60
        sta $05
*       rts

;-------------------------------------[ Get object coordinates ]------------------------------------

GetObjCoords:
LD79F:  ldx PageIndex                   ;Load index into object RAM to find proper object.
LD7A1:  lda ObjectY,x                   ;
LD7A4:  sta $02                         ;Load and save temp copy of object y coord.
LD7A6:  lda ObjectX,x                   ;
LD7A9:  sta $03                         ;Load and save temp copy of object x coord.
LD7AB:  lda ObjectHi,x                  ;
LD7AE:  sta $0B                         ;Load and save temp copy of object nametable.
LD7B0:  jmp MakeCartRAMPtr              ;($E96A)Find object position in room RAM.

;---------------------------------------------------------------------------------------------------

UpdateElevator:
        ldx #$20
        stx PageIndex
        lda ObjAction,x
        jsr ChooseRoutine

; Pointer table to elevator handlers

        .word ExitSub       ;($C45C) rts
        .word ElevatorIdle
        .word $D80E
        .word ElevatorMove
        .word ElevatorScroll
        .word $D8A3
        .word $D8BF
        .word $D8A3
        .word ElevatorMove
        .word ElevatorStop

        ElevatorIdle:
        lda SamusOnElevator
        beq ShowElevator
        lda #$04
        bit $032F       ; elevator direction in bit 7 (1 = up)
        bpl +
        asl             ; btn_UP
*       and Joy1Status
        beq ShowElevator
    ; start elevator!
        jsr StopVertMovement            ;($D147)
        sty AnimDelay
        sty SamusGravity
        tya
        sta ObjVertSpeed,x
        inc ObjAction,x
        lda #sa_Elevator
        sta ObjAction
        lda #an_SamusFront
        jsr SetSamusAnim
        lda #128
        sta ObjectX     ; center
        lda #112
        sta ObjectY     ; center
        ShowElevator:
        lda FrameCount
        lsr
        bcc --    ; only display elevator at odd frames
        jmp DrawFrame       ; display elevator

LD80E:  lda ScrollX
        bne +
        lda MirrorCntrl
        ora #$08
        sta MirrorCntrl
        lda ScrollDir
        and #$01
        sta ScrollDir
        inc ObjAction,x
        jmp ShowElevator

*       lda #$80
        sta ObjectX
        lda ObjectX,x
        sec
        sbc ScrollX
        bmi +
        jsr ScrollLeft
        jmp ShowElevator

*       jsr ScrollRight
        jmp ShowElevator

        ElevatorMove:
        lda $030F,x
        bpl ++    ; branch if elevator going down
    ; move elevator up one pixel
        ldy ObjectY,x
        bne +
        jsr ToggleObjectHi
        ldy #240
*       dey
        tya
        sta ObjectY,x
        jmp ++

    ; move elevator down one pixel
*       inc ObjectY,x
        lda ObjectY,x
        cmp #240
        bne +
        jsr ToggleObjectHi
        lda #$00
        sta ObjectY,x
*       cmp #$83
        bne +      ; move until Y coord = $83
        inc ObjAction,x
*       jmp ShowElevator

        ElevatorScroll:
        lda ScrollY
        bne ElevScrollRoom  ; scroll until ScrollY = 0
        lda #$4E
        sta AnimResetIndex
        lda #$41
        sta AnimIndex
        lda #$5D
        sta AnimResetIndex,x
        lda #$50
        sta AnimIndex,x
        inc ObjAction,x
        lda #$40
        sta Timer1
        jmp ShowElevator

        ElevScrollRoom:
        lda $030F,x
        bpl +      ; branch if elevator going down
        jsr ScrollUp
        jmp ShowElevator

*       jsr ScrollDown
        jmp ShowElevator

LD8A3:  inc ObjAction,x
        lda ObjAction,x
        cmp #$08        ; ElevatorMove
        bne +
        lda #$23
        sta $0303,x
        lda #an_SamusFront
        jsr SetSamusAnim
        jmp ShowElevator

*       lda #$01
        jmp AnimDrawObject

LD8BF:  lda $030F,x
        tay
        cmp #$8F        ; Leads-To-Ending elevator?
        bne +
    ; Samus made it! YAY!
        lda #$07
        sta MainRoutine
        inc AtEnding
        ldy #$00
        sty $33
        iny
        sty SwitchPending   ; switch to bank 0
        lda #$1D        ; ending
        sta TitleRoutine
        rts

*       tya
        bpl ++
        ldy #$00
        cmp #$84
        bne +
        iny
*       tya
*       ora #$10
        jsr LCA18
        lda PalToggle
        eor #$07
        sta PalToggle
        ldy InArea
        cpy #$12
        bcc +
        lda #$01
*       sta PalDataPending
        jsr WaitNMIPass_
        jsr SelectSamusPal
        jsr StartMusic                  ;($LD92C)Start music.
        jsr ScreenOn
        jsr CopyPtrs
        jsr DestroyEnemies
        ldx #$20
        stx PageIndex
        lda #$6B
        sta AnimResetIndex
        lda #$5F
        sta AnimIndex
        lda #$7A
        sta AnimResetIndex,x
        lda #$6E
        sta AnimIndex,x
        inc ObjAction,x
        lda #$40
        sta Timer1
        rts

StartMusic:
LD92C:  lda ElevatorStatus
        cmp #$06
        bne +
        lda $032F
        bmi ++
*       lda $95CD                       ;Load proper bit flag for area music.
        ldy ItemRoomMusicStatus
        bmi ++
        beq ++
*       lda #$81
        sta ItemRoomMusicStatus
        lda #$20                        ;Set flag to play item room music.

*       ora MusicInitFlag               ;
        sta MusicInitFlag               ;Store music flag info.
        rts                             ;

ElevatorStop:
        lda ScrollY
        bne ++    ; scroll until ScrollY = 0
        lda #sa_Stand
        sta ObjAction
        jsr LCF55
        ldx PageIndex   ; #$20
        lda #$01        ; ElevatorIdle
        sta ObjAction,x
        lda $030F,x
        eor #$80        ; switch elevator direction
        sta $030F,x
        bmi +
        jsr ToggleScroll
        sta MirrorCntrl
*       jmp ShowElevator
*       jmp ElevScrollRoom

SamusOnElevatorOrEnemy:
LD976:  lda #$00                        ;
        sta SamusOnElevator             ;Assume Samus is not on an elevator or on a frozen enemy.
        sta OnFrozenEnemy               ;
        tay
        ldx #$50
        jsr LF186
*       lda EnStatus,x
        cmp #$04
        bne +
        jsr LF152
        jsr LF1BF
        jsr LF1FA
        bcs +
        jsr LD9BA
        bne +
D99A:   inc OnFrozenEnemy               ;Samus is standing on a frozen enemy.
        bne ++
*       jsr Xminus16
        bpl --
*       lda ElevatorStatus
        beq +
        ldy #$00
        ldx #$20
        jsr LDC82
        bcs +
        jsr LD9BA
        bne +
        inc SamusOnElevator             ;Samus is standing on elevator.
*       rts

LD9BA:  lda $10
        and #$02
        bne +
        ldy $11
        iny
        cpy $04
        beq Exit8
*       lda SamusHit
        and #$38
        ora $10
        ora #$40
        sta SamusHit
Exit8:  rts

; UpdateStatues
; =============

        UpdateStatues:
        lda #$60
        sta PageIndex
        ldy $0360
        beq Exit8          ; exit if no statue present
        dey
        bne +
        jsr LDAB0
        ldy #$01
        jsr LDAB0
        bcs +
        inc $0360
*       ldy $0360
        cpy #$02
        bne +++
        lda KraidStatueStatus
        bpl +
        ldy #$02
        jsr LDAB0
*       lda $687C
        bpl +
        ldy #$03
        jsr LDAB0
*       bcs +
        inc $0360
*       ldx #$60
        jsr LDA1A
        ldx #$61
        jsr LDA1A
        jmp LDADA

LDA1A:  jsr LDA3D
        jsr LDA7C
        txa
        and #$01
        tay
        lda LDA3B,y
        sta $0363
        lda $681B,x
        beq +
        bmi +
        lda FrameCount
        lsr
        bcc ++    ; only display statue at odd frames
*       jmp DrawFrame       ; display statue

LDA39:  .byte $88
        .byte $68
LDA3B:  .byte $65
        .byte $66

LDA3D:  lda $0304,x
        bmi +
        lda #$01
        sta $0304,x
        lda $030F,x
        and #$0F
        beq +
        inc $0304,x
        dec $030F,x
        lda $030F,x
        and #$0F
        bne +
        lda $0304,x
        ora #$80
        sta $0304,x
        sta $681B,x
        inc $0304,x
        txa
        pha
        and #$01
        pha
        tay
        jsr LDAB0
        pla
        tay
        iny
        iny
        jsr LDAB0
        pla
        tax
*       rts

LDA7C:  lda $030F,x
        sta $036D
        txa
        and #$01
        tay
        lda LDA39,y
        sta $036E
        lda $681B,x
        beq +
        bmi +
        lda $0304,x
        cmp #$01
        bne +
        lda $0306,x
        beq +
        dec $030F,x
        lda $0683
        ora #$10
        sta $0683
*       lda #$00
        sta $0306,x
        rts

LDAB0:  lda Table0E,y
        sta $05C8
        lda $036C
        asl
        asl
        ora Table1B,y
        sta $05C9
        lda #$09
        sta $05C3
        lda #$C0
        sta PageIndex
        jsr DrawTileBlast
        lda #$60
        sta PageIndex
        rts

; Table used by above subroutine

Table0E:
        .byte $30
        .byte $AC
        .byte $F0
        .byte $6C
Table1B:
        .byte $61
        .byte $60
        .byte $60
        .byte $60

LDADA:  lda $54
        bmi Exit0
        lda DoorStatus
        bne Exit0
        lda KraidStatueStatus
        and $687C
        bpl Exit0
        sta $54
        ldx #$70
        ldy #$08
*       lda #$03
        sta $0500,x
        tya
        asl
        sta $0507,x
        lda #$04
        sta TileType,x
        lda $036C
        asl
        asl
        ora #$62
        sta TileWRAMHi,x
        tya
        asl
        adc #$08
        sta TileWRAMLo,x
        jsr Xminus16
        dey
        bne -
Exit0:  rts

; CheckMissileToggle
; ==================
; Toggles between bullets/missiles (if Samus has any missiles).

CheckMissileToggle:
        lda MissileCount
        beq Exit0       ; exit if Samus has no missiles
        lda Joy1Change
        ora Joy1Retrig
        and #$20        
        beq Exit0       ; exit if SELECT not pressed
        lda MissileToggle
        eor #$01        ; 0 = fire bullets, 1 = fire missiles
        sta MissileToggle
        jmp SelectSamusPal

; MakeBitMask
; ===========
;In: Y = bit index. Out: A = bit Y set, other 7 bits zero.

MakeBitMask:
LDB2F:  sec
LDB30:  lda #$00
LDB32:* rol
LDB33:  dey
LDB34:  bpl -
LDB36:* rts

;------------------------------------------[ Update items ]-----------------------------------------

UpdateItems:
LDB37:  lda #$40                        ;PowerUp RAM starts at $0340.
LDB39:  sta PageIndex                   ;
LDB3B:  ldx #$00                        ;Check first item slot.
LDB3D:  jsr CheckOneItem                ;($DB42)Check current item slot.
LDB40:  ldx #$08                        ;Check second item slot.

CheckOneItem:
LDB42:  stx ItemIndex                   ;First or second item slot index(#$00 or #$08).
LDB44:  ldy PowerUpType,x               ;
LDB47:  iny                             ;Is no item present in item slot(#$FF)?-->
LDB48:  beq -                           ;If so, branch to exit.

LDB4A:  lda PowerUpYCoord,x             ;
LDB4D:  sta PowerUpY                    ;
LDB50:  lda PowerUpXCoord,x             ;Store y, x and name table coordinates of power up item.
LDB53:  sta PowerUpX                    ;
LDB56:  lda PowerUpNameTable,x          ;
LDB59:  sta PowerUpHi                   ;
LDB5C:  jsr GetObjCoords                ;($D79F)Find object position in room RAM.
LDB5F:  ldx ItemIndex                   ;Index to proper power up item.
LDB61:  ldy #$00                        ;Reset index.
LDB63:  lda ($04),y                     ;Load pointer into room RAM.
LDB65:  cmp #$A0                        ;Is object being placed on top of a solid tile?-->
LDB67:  bcc -                           ;If so, branch to exit.
LDB69:  lda PowerUpType,x               ;
LDB6C:  and #$0F                        ;Load power up type byte and keep only bits 0 thru 3.
LDB6E:  ora #$50                        ;Set bits 4 and 6.
LDB70:  sta PowerUpAnimFrame            ;Save index to find object animation.
LDB73:  lda FrameCount                  ;
LDB75:  lsr                             ;Color affected every other frame.
LDB76:  and #$03                        ;the 2 LSBs of object control byte change palette of object.
LDB78:  ora #$80                        ;Indicate ObjectCntrl contains valid data by setting MSB.
LDB7A:  sta ObjectCntrl                 ;Change color of item every other frame.
LDB7C:  lda SpritePagePos               ;Load current index into sprite RAM.
LDB7E:  pha                             ;Temp save sprite RAM position.
LDB7F:  lda PowerUpAnimIndex,x          ;Load entry into FramePtrTable for item animation.
LDB82:  jsr DrawFrame                   ;($DE4A)Display special item.

LDB85:  pla                             ;Restore sprite page position byte.
LDB86:  cmp SpritePagePos               ;Was power up item successfully drawn?-->
LDB88:  beq Exit9                       ;If not, branch to exit.
LDB8A:  tax                             ;Store sprite page position in x.
LDB8B:  ldy ItemIndex                   ;Load index to proper power up data slot.
LDB8D:  lda PowerUpType,y               ;Reload power up type data.
LDB90:  ldy #$01                        ;Set power up color for ice beam orb.
LDB92:  cmp #$07                        ;Is power up item the ice beam?-->
LDB94:  beq +                           ;If so, branch.

LDB96:  dey                             ;Set power up color for long/wave beam orb.
LDB97:  cmp #$06                        ;Is power up item the wave beam?-->
LDB99:  beq +                           ;If so, branch.
LDB9B:  cmp #$02                        ;Is power up item the long beam?-->
LDB9D:  bne ++                          ;If not, branch.
LDB9F:* tya                             ;Transfer color data to A.
LDBA0:  sta Sprite01RAM+2,x             ;Store power up color for beam weapon.
LDBA3:  lda #$FF                        ;Indicate power up obtained is a beam weapon.

LDBA5:* pha                             ;Temporarily store power up type.
LDBA6:  ldx #$00                        ;Index to object 0(Samus).
LDBA8:  ldy #$40                        ;Index to object 1(power up).
LDBAA:  jsr AreObjectsTouching          ;($DC7F)Determine if Samus is touching power up.
LDBAD:  pla                             ;Restore power up type byte.
LDBAE:  bcs Exit9                       ;Carry clear=Samus touching power up. Carry set=not touching.

LDBB0:  tay                             ;Store power-up type byte in Y.
LDBB1:  jsr PowerUpMusic                ;($CBF9)Power up obtained! Play power up music.
LDBB4:  ldx ItemIndex                   ;X=index to power up item slot.
LDBB6:  iny                             ;Is item obtained a beam weapon?-->
LDBB7:  beq +                           ;If so, branch.
LDBB9:  lda PowerUpNameTable,x          ;
LDBBC:  sta $08                         ;Temp storage of nametable and power-up type in $08-->
LDBBE:  lda PowerUpType,x               ;and $09 respectively.
LDBC1:  sta $09                         ;
LDBC3:  jsr GetItemXYPos                ;($DC1C)Get proper X and Y coords of item, save in history.
LDBC6:* lda PowerUpType,x               ;Get power-up type byte again.
LDBC9:  tay                             ;
LDBCA:  cpy #$08                        ;Is power-up item a missile or energy tank?-->
LDBCC:  bcs ++++                        ;If so, branch.
LDBCE:  cpy #$06                        ;Is item the wave beam or ice beam?-->
LDBD0:  bcc +                           ;If not, branch.
LDBD2:  lda SamusGear                   ;Clear status of wave beam and ice beam power ups.
LDBD5:  and #$3F                        ;
LDBD7:  sta SamusGear                   ;Remove beam weapon data from Samus gear byte.
LDBDA:* jsr MakeBitMask                 ;($DB2F)Create a bit mask for beam weapon just obtained.
LDBDD:  ora SamusGear                   ;
LDBE0:  sta SamusGear                   ;Update Samus gear with new beam weapon.
LDBE3:* lda #$FF                        ;
LDBE5:  sta PowerUpDelay                ;Initiate delay while power up music plays.
LDBE8:  sta PowerUpType,x               ;Clear out item data from RAM.
LDBEB:  ldy ItemRoomMusicStatus         ;Is Samus not in an item room?-->
LDBED:  beq +                           ;If not, branch.
LDBEF:  ldy #$01                        ;Restart item room music after special item music is done.
LDBF1:* sty ItemRoomMusicStatus         ;
LDBF3:  jmp SelectSamusPal              ;($CB73)Set Samus new palette.

Exit9:
LDBF6:  rts                             ;Exit for multiple routines above.

MissileEnergyPickup:
LDBF7:* beq +                           ;Branch if item is an energy tank.
LDBF9:  lda #$05                        ;
LDBFB:  jsr AddToMaxMissiles            ;($DD97)Increase missile capacity by 5.
LDBFE:  bne ---                         ;Branch always.

LDC00:* lda TankCount                   ;
LDC03:  cmp #$06                        ;Has Samus got 6 energy tanks?-->
LDC05:  beq +                           ;If so, she can't have any more.-->
LDC07:  inc TankCount                   ;Otherwise give her a new tank.
LDC0A:* lda TankCount                   ;
LDC0D:  jsr Amul16                      ;Get tank count and shift into upper nibble.
LDC10:  ora #$09                        ;
LDC12:  sta HealthHi                    ;Set new tank count. Upper health digit set to 9.
LDC15:  lda #$99                        ;Max out low health digit.
LDC17:  sta HealthLo                    ;Health is now FULL!
LDC1A:  bne -----                       ;Branch always.

;It is possible for the current nametable in the PPU to not be the actual nametable the special item
;is on so this function checks for the proper location of the special item so the item ID can be
;properly calculated.

GetItemXYPos:
LDC1C:  lda MapPosX                     ;
LDC1E:  sta $07                         ;Temp storage of Samus map position x and y in $07-->
LDC20:  lda MapPosY                     ;and $06 respectively.
LDC22:  sta $06                         ;
LDC24:  lda ScrollDir                   ;Load scroll direction and shift LSB into carry bit.
LDC26:  lsr                             ;
LDC27:  php                             ;Temp storage of processor status.
LDC28:  beq +                           ;Branch if scrolling up/down.
LDC2A:  bcc ++                          ;Branch if scrolling right.

;Scrolling left.
LDC2C:  lda ScrollX                     ;Unless the scroll x offset is 0, the actual room x pos-->
LDC2E:  beq ++                          ;needs to be decremented in order to be correct.
LDC30:  dec $07                         ;
LDC32:  bcs ++                          ;Branch always.

LDC34:* bcc +                           ;Branch if scrolling up.

;Scrolling down.
LDC36:  lda ScrollY                     ;Unless the scroll y offset is 0, the actual room y pos-->
LDC38:  beq +                           ;needs to be decremented in order to be correct.
LDC3A:  dec $06                         ;

LDC3C:* lda PPUCNT0ZP                   ;If item is on the same nametable as current nametable,-->
LDC3E:  eor $08                         ;then no further adjustment to item x and y position needed.
LDC40:  and #$01                        ;
LDC42:  plp                             ;Restore the processor status and clear the carry bit.
LDC43:  clc                             ;
LDC44:  beq +                           ;If Scrolling up/down, branch to adjust item y position.

LDC46:  adc $07                         ;Scrolling left/right. Make any necessary adjustments to-->
LDC48:  sta $07                         ;item x position before writing to unique item history.

LDC4A:  jmp AddItemToHistory            ;($DC51)Add unique item to unique item history.

LDC4D:* adc $06                         ;Scrolling up/down. Make any necessary adjustments to-->
LDC4F:  sta $06                         ;item y position before writing to unique item history.

AddItemToHistory:
LDC51:  jsr CreateItemID                ;($DC67)Create an item ID to put into unique item history.
LDC54:  ldy NumberOfUniqueItems         ;Store number of uniqie items in Y.
LDC57:  lda $06                         ;
LDC59:  sta UniqueItemHistory,y         ;Store item ID in inuque item history.
LDC5C:  lda $07                         ;
LDC5E:  sta UniqueItemHistory+1,y       ;
LDC61:  iny                             ;Add 2 to Y. 2 bytes ber unique item.
LDC62:  iny                             ;
LDC63:  sty NumberOfUniqueItems         ;Store new number of unique items.
LDC66:  rts                             ;

;------------------------------------------[ Create item ID ]-----------------------------------------

;The following routine creates a unique two byte item ID number for that item.  The description
;of the format of the item ID number is as follows:
;
;IIIIIIXX XXXYYYYY. I = item type, X = X coordinate on world map, Y = Y coordinate
;on world map.  The items have the following values of IIIIII:
;High jump     = 000001
;Long beam     = 000010 (Not considered a unique item).
;Screw attack  = 000011
;Maru Mari     = 000100
;Varia suit    = 000101
;Wave beam     = 000110 (Not considered a unique item).
;Ice beam      = 000111 (Not considered a unique item).
;Energy tank   = 001000
;Missiles      = 001001
;Missile door  = 001010
;Bombs         = 001100
;Mother brain  = 001110
;1st Zeebetite = 001111
;2nd Zeebetite = 010000
;3rd Zeebetite = 010001
;4th Zeebetite = 010010
;5th Zeebetite = 010011
;
;The results are stored in $06(upper byte) and $07(lower byte).

CreateItemID:
LDC67:  lda $07                         ;Load x map position of item.
LDC69:  jsr Amul32                      ;($C2C$)*32. Move lower 3 bytes to upper 3 bytes.
LDC6C:  ora $06                         ;combine Y coordinates into data byte.
LDC6E:  sta $06                         ;Lower data byte complete. Save in $06.
LDC70:  lsr $07                         ;
LDC72:  lsr $07                         ;Move upper two bits of X coordinate to LSBs.
LDC74:  lsr $07                         ;
LDC76:  lda $09                         ;Load item type bits.
LDC78:  asl                             ;Move the 6 bits of item type to upper 6 bits of byte.
LDC79:  asl                             ;
LDC7A:  ora $07                         ;Add upper two bits of X coordinate to byte.
LDC7C:  sta $07                         ;Upper data byte complete. Save in #$06.
LDC7E:  rts                             ;

;-----------------------------------------------------------------------------------------------------

AreObjectsTouching:
LDC7F:  jsr LF186
LDC82:  jsr LF172
LDC85:  jsr LF1A7
LDC88:  jmp LF1FA

;The following table is used to rotate the sprites of both Samus and enemies when they explode.

ExplodeRotationTbl:
LDC8B:  .byte $00                       ;No sprite flipping.
LDC8C:  .byte $80                       ;Flip sprite vertically.
LDC8D:  .byte $C0                       ;Flip sprite vertically and horizontally.
LDC8E:  .byte $40                       ;Flip sprite horizontally.

; UpdateObjAnim
; =============
; Advance to object's next frame of animation

UpdateObjAnim:
LDC8F:  ldx PageIndex
        ldy AnimDelay,x
        beq +      ; is it time to advance to the next anim frame?
        dec AnimDelay,x     ; nope
        bne +++   ; exit if still not zero (don't update animation)
*       sta AnimDelay,x     ; set initial anim countdown value
        ldy AnimIndex,x
*       lda ObjectAnimIndexTbl,y                ;($8572)Load frame number.
        cmp #$FF        ; has end of anim been reached?
        beq ++
        sta AnimFrame,x     ; store frame number
        iny          ; inc anim index
        tya
        sta AnimIndex,x     ; store anim index
*       rts

*       ldy AnimResetIndex,x     ; reset anim frame index
        jmp ---    ; do first frame of animation

LDCB7:  pha
        lda #$00
        sta $06
        pla
        bpl +
        dec $06
*       clc
        rts

;--------------------------------[ Get sprite control byte ]-----------------------------------------

;The sprite control byte extracted from the frame data has the following format: AABBXXXX.
;Where AA are the two bits used to control the horizontal and verticle mirroring of the
;sprite and BB are the two bits used control the sprite colors. XXXX is the entry number
;in the PlacePtrTbl used to place the sprite on the screen.

GetSpriteCntrlData:
LDCC3:  ldy #$00                        ;
LDCC5:  sty $0F                         ;Clear index into placement data.
LDCC7:  lda ($00),y                     ;Load control byte from frame pointer data.
LDCC9:  sta $04                         ;Store value in $04 for processing below.
LDCCB:  tax                             ;Keep a copy of the value in x as well.
LDCCC:  jsr Adiv16                      ;($C2BF)Move upper 4 bits to lower 4 bits.
LDCCF:  and #$03                        ;
LDCD1:  sta $05                         ;The following lines take the upper 4 bits in the-->
LDCD3:  txa                             ;control byte and transfer bits 4 and 5 into $05 bits 0-->
LDCD4:  and #$C0                        ;and 1(sprite color bits).  Bits 6 and 7 are-->
LDCD6:  ora #$20                        ;transferred into $05 bits 6 and 7(sprite flip bits).-->
LDCD8:  ora $05                         ;bit 5 is then set(sprite always drawn behind background).
LDCDA:  sta $05                         ;
LDCDC:  lda ObjectCntrl                 ;Extract bit from control byte that controls the
LDCDE:  and #$10                        ;object mirroring.
LDCE0:  asl                             ;
LDCE1:  asl                             ;
LDCE2:  eor $04                         ;Move it to the bit 6 position and use it to flip the-->
LDCE4:  sta $04                         ;horizontal mirroring of the sprite if set.
LDCE6:  lda ObjectCntrl                 ;
LDCE8:  bpl +                           ;If MSB is set in ObjectCntrl, use its flip bits(6 and 7).
LDCEA:  asl ObjectCntrl                 ;
LDCEC:  jsr SpriteFlipBitsOveride       ;($E038)Use object flip bits as priority over sprite flip bits. 
LDCEF:* txa                             ;Discard upper nibble so only entry number into-->
LDCF0:  and #$0F                        ;PlacePtrTbl remains.
LDCF2:  asl                             ;*2. pointers in PlacePntrTbl are 2 bytes in size.
LDCF3:  tax                             ;Transfer to X to use as an index to find proper-->
LDCF4:  rts                             ;placement data segment.

;-----------------------------------------------------------------------------------------------------

LDCF5:  jsr ClearObjectCntrl            ;($DF2D)Clear object control byte.
        pla
        pla
        ldx PageIndex
LDCFC:  lda InArea
        cmp #$13
        bne +
        lda EnDataIndex,x
        cmp #$04
        beq +++++
        cmp #$02
        beq +++++
*       lda $040C,x
        asl
        bmi LDD75
        jsr LF74B
        sta $00
        jsr $80B0
        and #$20
        sta EnDataIndex,x
        lda #$05
        sta EnStatus,x
        lda #$60
        sta $040D,x
        lda RandomNumber1
        cmp #$10
        bcc LDD5B
*       and #$07
        tay
        lda ItemDropTbl,y
        sta EnAnimFrame,x
        cmp #$80
        bne ++
        ldy MaxMissilePickup
        cpy CurrentMissilePickups
        beq LDD5B
        lda MaxMissiles
        beq LDD5B
        inc CurrentMissilePickups
*       rts

*       ldy MaxEnergyPickup
        cpy CurrentEnergyPickups
        beq LDD5B
        inc CurrentEnergyPickups
        cmp #$89
        bne --
        lsr $00
        bcs --

LDD5B:  ldx PageIndex
        lda InArea
        cmp #$13
        beq ++
*       jmp KillObject                  ;($FA18)Free enemy data slot.

*       lda RandomNumber1
        ldy #$00
        sty CurrentEnergyPickups
        sty CurrentMissilePickups
        iny
        sty MaxMissilePickup
        sty MaxEnergyPickup
        bne -----

LDD75:  jsr PowerUpMusic
        lda InArea
        and #$0F
        sta MiniBossKillDelay
        lsr
        tay
        sta MaxMissiles,y
        lda #75
        jsr AddToMaxMissiles
        bne LDD5B

LDD8B:  ldx PageIndex
        lda EnAnimFrame,x
        cmp #$F7
        bne +++
        jmp ClearObjectCntrl            ;($DF2D)Clear object control byte.

; AddToMaxMissiles
; ================
; Adds A to both MissileCount & MaxMissiles, storing the new count
; (255 if it overflows)

AddToMaxMissiles:
        pha                             ;Temp storage of # of missiles to add.
        clc
        adc MissileCount
        bcc +
        lda #$FF
*       sta MissileCount
        pla
        clc
        adc MaxMissiles
        bcc +
        lda #$FF
*       sta MaxMissiles
        rts

*       lda EnYRoomPos,x
        sta $0A  ; Y coord
        lda EnXRoomPos,x
        sta $0B  ; X coord
        lda EnNameTable,x
        sta $06  ; hi coord
        lda EnAnimFrame,x
        asl
        tay
        lda ($41),y
        bcc +
        lda ($43),y
*       sta $00
        iny
        lda ($41),y
        bcc +
        lda ($43),y
*       sta $01
        jsr GetSpriteCntrlData          ;($DCC3)Get place pointer index and sprite control data.
        tay
        lda ($45),y
        sta $02
        iny
        lda ($45),y
        sta $03
        ldy #$00
        cpx #$02
        bne +
        ldx PageIndex
        inc EnCounter,x
        lda EnCounter,x
        pha
        and #$03
        tax
        lda $05
        and #$3F
        ora ExplodeRotationTbl,x
        sta $05
        pla
        cmp #$19
        bne +
        jmp LDCF5

*       ldx PageIndex
        iny
        lda ($00),y
        sta EnRadY,x
        jsr ReduceYRadius               ;($DE3D)Reduce temp y radius by #$10.
        iny
        lda ($00),y
        sta EnRadX,x
        sta $09
        iny
        sty $11
        jsr IsObjectVisible             ;($DFDF)Determine if object is within screen boundaries.
        txa
        asl
        sta $08
        ldx PageIndex
        lda $0405,x
        and #$FD
        ora $08
        sta $0405,x
        lda $08
        beq ++
        jmp LDEDE

;----------------------------------------[ Item drop table ]-----------------------------------------

;The following table determines what, if any, items an enemy will drop when it is killed.

ItemDropTbl:
LDE35:  .byte $80                       ;Missile.
LDE36:  .byte $81                       ;Energy.
LDE37:  .byte $89                       ;No item.
LDE38:  .byte $80                       ;Missile.
LDE39:  .byte $81                       ;Energy.
LDE3A:  .byte $89                       ;No item.
LDE3B:  .byte $81                       ;Energy.
LDE3C:  .byte $89                       ;No item.

;------------------------------------[ Object drawing routines ]-------------------------------------

;The following function effectively sets an object's temporary y radius to #$00 if the object
;is 4 tiles tall or less.  If it is taller, #$10 is subtracted from the temporary y radius.

ReduceYRadius:
LDE3D:  sec                             ;
LDE3E:  sbc #$10                        ;Subtract #$10 from object y radius.
LDE40:  bcs +                           ;If number is still a positive number, branch to store value.
LDE42:  lda #$00                        ;Number is negative.  Set Y radius to #$00.
LDE44:* sta $08                         ;Store result and return.
LDE46:  rts                             ;

AnimDrawObject:
LDE47:  jsr UpdateObjAnim               ;($DC8F)Update animation if needed.

DrawFrame:
LDE4A:  ldx PageIndex                   ;Get index to proper object to work with.
LDE4C:  lda AnimFrame,x                 ;
LDE4F:  cmp #$F7                        ;Is the frame valid?-->
LDE51:  bne ++                          ;Branch if yes.
LDE53:* jmp ClearObjectCntrl            ;($DF2D)Clear object control byte.
LDE56:* cmp #$07                        ;Is the animation of Samus facing forward?-->
LDE58:  bne +                           ;If not, branch.

LDE5A:  lda ObjectCntrl                 ;Ensure object mirroring bit is clear so Samus'-->
LDE5C:  and #$EF                        ;sprite appears properly when going up and down-->
LDE5E:  sta ObjectCntrl                 ;elevators.

LDE60:* lda ObjectY,x                   ;
LDE63:  sta $0A                         ;
LDE65:  lda ObjectX,x                   ;Copy object y and x room position and name table-->
LDE68:  sta $0B                         ;data into $0A, $0B and $06 respectively.
LDE6A:  lda ObjectHi,x                  ;
LDE6D:  sta $06                         ;
LDE6F:  lda AnimFrame,x                 ;Load A with index into FramePtrTable.
LDE72:  asl                             ;*2. Frame pointers are two bytes.
LDE73:  tax                             ;X is now the index into the FramePtrTable.
LDE74:  lda FramePtrTable,x             ;
LDE77:  sta $00                         ;
LDE79:  lda FramePtrTable+1,x           ;Entry from FramePtrTable is stored in $0000.
LDE7C:  sta $01                         ;
LDE7E:  jsr GetSpriteCntrlData          ;($DCC3)Get place pointer index and sprite control data.
LDE81:  lda PlacePtrTable,x             ;
LDE84:  sta $02                         ;
LDE86:  lda PlacePtrTable+1,x           ;Store pointer from PlacePtrTbl in $0002.
LDE89:  sta $03                         ;
LDE8B:  lda IsSamus                     ;Is Samus the object being drawn?-->
LDE8D:  beq +                           ;If not, branch.

;Special case for Samus exploding.
LDE8F:  cpx #$0E                        ;Is Samus exploding?-->
LDE91:  bne +                           ;If not, branch to skip this section of code.
LDE93:  ldx PageIndex                   ;X=0.
LDE95:  inc ObjectCounter               ;Incremented every frame during explode sequence.-->
LDE97:  lda ObjectCounter               ;Bottom two bits used for index into ExplodeRotationTbl.
LDE99:  pha                             ;Save value of A.
LDE9A:  and #$03                        ;Use 2 LSBs for index into ExplodeRotationTbl.
LDE9C:  tax                             ;
LDE9D:  lda $05                         ;Drop mirror control bits from sprite control byte.
LDE9F:  and #$3F                        ;
LDEA1:  ora ExplodeRotationTbl,x        ;Use mirror control bytes from table(Base is $DC8B).
LDEA4:  sta $05                         ;Save modified sprite control byte.
LDEA6:  pla                             ;Restore A
LDEA7:  cmp #$19                        ;After 25 frames, Move on to second part of death--> 
LDEA9:  bne +                           ;handler, else branch to skip the rest of this code.
LDEAB:  ldx PageIndex                   ;X=0.
LDEAD:  lda #sa_Dead2                   ;
LDEAF:  sta ObjAction,x                 ;Move to next part of the death handler.
LDEB2:  lda #$28                        ;
LDEB4:  sta AnimDelay,x                 ;Set animation delay for 40 frames(.667 seconds).
LDEB7:  pla                             ;Pull last return address off of the stack.
LDEB8:  pla                             ;
LDEB9:  jmp ClearObjectCntrl            ;($DF2D)Clear object control byte.

LDEBC:* ldx PageIndex                   ;
LDEBE:  iny                             ;Increment to second frame data byte.
LDEBF:  lda ($00),y                     ;
LDEC1:  sta ObjRadY,x                   ;Get verticle radius in pixles of object.
LDEC3:  jsr ReduceYRadius               ;($DE3D)Reduce temp y radius by #$10.
LDEC6:  iny                             ;Increment to third frame data byte.
LDEC7:  lda ($00),y                     ;Get horizontal radius in pixels of object.
LDEC9:  sta ObjRadX,x                   ;
LDECB:  sta $09                         ;Temp storage for object x radius.
LDECD:  iny                             ;Set index to 4th byte of frame data.
LDECE:  sty $11                         ;Store current index into frame data.
LDED0:  jsr IsObjectVisible             ;($DFDF)Determine if object is within the screen boundaries.
LDED3:  txa                             ;
LDED4:  ldx PageIndex                   ;Get index to object.
LDED6:  sta ObjectOnScreen,x            ;Store visibility status of object.
LDEDB:  tax                             ;
LDEDC:  beq +                           ;Branch if object is not within the screen boundaries.
LDEDE:  ldx SpritePagePos               ;Load index into next unused sprite RAM segment.
LDEE0:  jmp DrawSpriteObject            ;($DF19)Start drawing object.

LDEE3:* jmp ClearObjectCntrl            ;($DF2D)Clear object control byte then exit.

WriteSpriteRAM:
LDEE6:* ldy $0F                         ;Load index for placement data.
LDEE8:  jsr YDisplacement               ;($DF6B)Get displacement for y direction.
LDEEB:  adc $10                         ;Add initial Y position.
LDEED:  sta Sprite00RAM,x               ;Store sprite Y coord.
LDEF0:  dec Sprite00RAM,x               ;Because PPU uses Y + 1 as real Y coord.
LDEF3:  inc $0F                         ;Increment index to next byte of placement data.
LDEF5:  ldy $11                         ;Get index to frame data.
LDEF7:  lda ($00),y                     ;Tile value.
LDEF9:  sta Sprite00RAM+1,x             ;Store tile value in sprite RAM.
LDEFC:  lda ObjectCntrl                 ;
LDEFE:  asl                             ;Move horizontal mirror control byte to bit 6 and-->
LDEFF:  asl                             ;discard all other bits.
LDF00:  and #$40                        ;
LDF02:  eor $05                         ;Use it to override sprite horz mirror bit.
LDF04:  sta Sprite00RAM+2,x             ;Store sprite control byte in sprite RAM.
LDF07:  inc $11                         ;Increment to next byte of frame data.
LDF09:  ldy $0F                         ;Load index for placement data.
LDF0B:  jsr XDisplacement               ;($DFA3)Get displacement for x direction.
LDF0E:  adc $0E                         ;Add initial X pos
LDF10:  sta Sprite00RAM+3,x             ;Store sprite X coord
LDF13:  inc $0F                         ;Increment to next placement data byte.
LDF15:  inx                             ;
LDF16:  inx                             ;
LDF17:  inx                             ;Advance to next sprite.
LDF18:  inx                             ;

DrawSpriteObject:
LDF19:  ldy $11                         ;Get index into frame data.

GetNextFrameByte:
LDF1B:  lda ($00),y                     ;Get next frame data byte.
LDF1D:  cmp #$FC                        ;If byte < #$FC, byte is tile data. If >= #$FC, byte is--> 
LDF1F:  bcc WriteSpriteRAM              ;frame data control info. Branch to draw sprite.
LDF21:  beq OffsetObjectPosition        ;#$FC changes object's x and y position.
LDF23:  cmp #$FD                        ;
LDF25:  beq GetNewControlByte           ;#$FD sets new control byte information for the next sprites.
LDF27:  cmp #$FE                        ;#$FE skips next sprite placement x and y bytes.
LDF29:  beq SkipPlacementData           ;
LDF2B:  stx SpritePagePos               ;Keep track of current position in sprite RAM.

ClearObjectCntrl:
LDF2D:  lda #$00                        ;
LDF2F:  sta ObjectCntrl                 ;Clear object control byte.
LDF31:  rts                             ;

SkipPlacementData:
LDF32:* inc $0F                         ;Skip next y and x placement data bytes.
LDF34:  inc $0F                         ;
LDF36:  inc $11                         ;Increment to next data item in frame data.
LDF38:  jmp DrawSpriteObject            ;($DF19)Draw next sprite.

GetNewControlByte:
LDF3B:* iny                             ;Increment index to next byte of frame data.
LDF3C:  asl ObjectCntrl                 ;If MSB of ObjectCntrl is not set, no overriding of-->
LDF3E:  bcc +                           ;flip bits needs to be performed.
LDF40:  jsr SpriteFlipBitsOveride       ;($E038)Use object flip bits as priority over sprite flip bits.
LDF43:  bne ++                          ;Branch always.
LDF45:* lsr ObjectCntrl                 ;Restore MSB of ObjectCntrl.
LDF47:  lda ($00),y                     ;
LDF49:  sta $05                         ;Save new sprite control byte.
LDF4B:* iny                             ;Increment past sprite control byte.
LDF4C:  sty $11                         ;Save index of frame data.
LDF4E:  jmp GetNextFrameByte            ;($DF1B)Load next frame data byte.

OffsetObjectPosition:
LDF51:* iny                             ;Increment index to next byte of frame data.
LDF52:  lda ($00),y                     ;This data byte is used to offset the object from-->
LDF54:  clc                             ;its current y positon.
LDF55:  adc $10                         ;
LDF57:  sta $10                         ;Add offset amount to object y screen position.
LDF59:  inc $11                         ;
LDF5B:  inc $11                         ;Increment past control byte and y offset byte.
LDF5D:  ldy $11                         ;
LDF5F:  lda ($00),y                     ;Load x offset data byte.
LDF61:  clc                             ;
LDF62:  adc $0E                         ;Add offset amount to object x screen position.
LDF64:  sta $0E                         ;
LDF66:  inc $11                         ;Increment past x offset byte.
LDF68:  jmp DrawSpriteObject            ;($DF19)Draw next sprite.

;----------------------------------[ Sprite placement routines ]-------------------------------------

YDisplacement:
LDF6B:  lda ($02),y                     ;Load placement data byte.
LDF6D:  tay                             ;
LDF6E:  and #$F0                        ;Check to see if this is placement data for the object-->
LDF70:  cmp #$80                        ;exploding.  If so, branch.
LDF72:  beq ++                          ;
LDF74:  tya                             ;Restore placement data byte to A.
LDF75:* bit $04                         ;
LDF77:  bmi NegativeDisplacement        ;Branch if MSB in $04 is set(Flips object).
LDF79:  clc                             ;Clear carry before returning.
LDF7A:  rts                             ;

ExplodeYDisplace:
LDF7B:* tya                             ;Transfer placement byte back into A.
LDF7C:  and #$0E                        ;Discard bits 7,6,5,4 and 0.
LDF7E:  lsr                             ;/2.
LDF7F:  tay                             ;
LDF80:  lda ExplodeIndexTbl,y           ;Index into ExplodePlacementTbl.
LDF83:  ldy IsSamus                     ;
LDF85:  bne +                           ;Is Samus the object exploding? if so, branch.
LDF87:  ldy PageIndex                   ;Load index to proper enemy data.
LDF89:  adc EnCounter,y                 ;Increment every frame enemy is exploding. Initial=#$01.
LDF8C:  jmp ++                          ;Jump to load explode placement data.


;Special case for Samus exploding.
LDF8F:* adc ObjectCounter               ;Increments every frame Samus is exploding. Initial=#$01.
LDF91:* tay                             ;
LDF92:  lda ExplodeIndexTbl+2,y         ;Get data from ExplodePlacementTbl.
LDF95:  pha                             ;Save data on stack.
LDF96:  lda $0F                         ;Load placement data index.
LDF98:  clc                             ;
LDF99:  adc #$0C                        ;Move index forward by 12 bytes. to find y-->
LDF9B:  tay                             ;placement data.
LDF9C:  pla                             ;Restore A with ExplodePlacementTbl data.
LDF9D:  clc                             ;
LDF9E:  adc ($02),y                     ;Add table displacements with sprite placement data.
LDFA0:  jmp ----                        ;Branch to add y placement values to sprite coords.

XDisplacement:
LDFA3:  lda ($02),y                     ;Load placement data byte.
LDFA5:  tay                             ;
LDFA6:  and #$F0                        ;Check to see if this is placement data for the object-->
LDFA8:  cmp #$80                        ;exploding.  If so, branch.
LDFAA:  beq +++                         ;
LDFAC:  tya                             ;Restore placement data byte to A.
LDFAD:* bit $04                         ;
LDFAF:  bvc +                           ;Branch if bit 6 cleared, else data is negative displacement.

NegativeDisplacement:
LDFB1:  eor #$FF                        ;
LDFB3:  sec                             ;NOTE:Setting carry makes solution 1 higher than expected.
LDFB4:  adc #$F8                        ;If flip bit is set in $04, this function flips the-->
LDFB6:* clc                             ;object by using two compliment minus 8(Each sprite is-->
LDFB7:  rts                             ;8x8 pixels).

ExplodeXDisplace:
LDFB8:* ldy PageIndex                   ;Load index to proper enemy slot.
LDFBA:  lda EnCounter,y                 ;Load counter value.
LDFBD:  ldy IsSamus                     ;Is Samus the one exploding?-->
LDFBF:  beq +                           ;If not, branch.
LDFC1:  lda ObjectCounter               ;Load object counter if it is Samus who is exploding.
LDFC3:* asl                             ;*2. Move sprite in x direction 2 pixels every frame.
LDFC4:  pha                             ;Store value on stack.
LDFC5:  ldy $0F                         ;
LDFC7:  lda ($02),y                     ;Load placement data byte.
LDFC9:  lsr                             ;
LDFCA:  bcs +                           ;Check if LSB is set. If not, the byte stored on stack-->
LDFCC:  pla                             ;Will be twos complimented and used to move sprite in-->
LDFCD:  eor #$FF                        ;the negative x direction.
LDFCF:  adc #$01                        ;
LDFD1:  pha                             ;
LDFD2:* lda $0F                         ;Load placement data index.
LDFD4:  clc                             ;
LDFD5:  adc #$0C                        ;Move index forward by 12 bytes. to find x-->
LDFD7:  tay                             ;placement data.
LDFD8:  pla                             ;Restore A with x displacement data.
LDFD9:  clc                             ;
LDFDA:  adc ($02),y                     ;Add x displacement with sprite placement data.
LDFDC:  jmp -----                       ;Branch to add x placement values to sprite coords.

;---------------------------------[ Check if object is on screen ]----------------------------------

;The following set of functions determine if an object is visible on the screen.  If the object
;is visible, X-1 when the function returns, X=0 if the object is not within the boundaries of the
;current screen.  The function needs to know what nametable is currently in the PPU, what nametable
;the object is on and what the scroll offsets are. 

IsObjectVisible:
LDFDF:  ldx #$01                        ;Assume object is visible on screen.
LDFE1:  lda $0A                         ;Object Y position in room.
LDFE3:  tay                             ;
LDFE4:  sec                             ;Subtract y scroll to find sprite's y position on screen.
LDFE5:  sbc ScrollY                     ;
LDFE7:  sta $10                         ;Store result in $10.
LDFE9:  lda $0B                         ;Object X position in room.
LDFEB:  sec                             ;
LDFEC:  sbc ScrollX                     ;Subtract x scroll to find sprite's x position on screen.
LDFEE:  sta $0E                         ;Store result in $0E.
LDFF0:  lda ScrollDir                   ;
LDFF2:  and #$02                        ;Is Samus scrolling left or right?-->
LDFF4:  bne HorzScrollCheck             ;($E01C)If so, branch.

VertScrollCheck:
LDFF6:  cpy ScrollY                     ;If object room pos is >= scrollY, set carry.
LDFF8:  lda $06                         ;Check if object is on different name table as current-->
LDFFA:  eor PPUCNT0ZP                   ;name table active in PPU.-->
LDFFC:  and #$01                        ;If not, branch.
LDFFE:  beq +                           ;
LE000:  bcs ++                          ;If carry is still set, sprite is not in screen boundaries.
LE002:  lda $10                         ;
LE004:  sbc #$0F                        ;Move sprite y position up 15 pixles.
LE006:  sta $10                         ;
LE008:  lda $09                         ;
LE00A:  clc                             ;If a portion of the object is outside the sceen-->
LE00B:  adc $10                         ;boundaries, treat object as if the whole thing is-->
LE00D:  cmp #$F0                        ;not visible.
LE00F:  bcc +++                         ;
LE011:  clc                             ;Causes next statement to branch always.
LE012:* bcc +                           ;
LE014:  lda $09                         ;If object is on same name table as the current one in-->
LE016:  cmp $10                         ;the PPU, check if part of object is out of screen--> 
LE018:  bcc ++                          ;boundaries.  If so, branch.
LE01A:* dex                             ;Sprite is not within screen boundaries. Decrement X.
LE01B:* rts                             ;

HorzScrollCheck:
LE01C:  lda $06                         ;
LE01E:  eor PPUCNT0ZP                   ;Check if object is on different name table as current-->
LE020:  and #$01                        ;name table active in PPU.-->
LE022:  beq +                           ;If not, branch.
LE024:  bcs ++                          ;If carry is still set, sprite is not in screen boundaries.
LE026:  lda $09                         ;
LE028:  clc                             ;If a portion of the object is outside the sceen-->
LE029:  adc $0E                         ;boundaries, treat object as if the whole thing is-->
LE02B:  bcc +++                         ;not visible.
LE02D:  clc                             ;Causes next statement to branch always.
LE02E:* bcc +                           ;
LE030:  lda $09                         ;If object is on same name table as the current one in-->
LE032:  cmp $0E                         ;the PPU, check if part of object is out of screen--> 
LE034:  bcc ++                          ;boundaries.  If so, branch.
LE036:* dex                             ;Sprite is not within screen boundaries. Decrement X.
LE037:* rts                             ;

;------------------------[ Override sprite flip bits with object flip bits ]-------------------------

;If the MSB is set in ObjectCntrl, its two upper bits that control sprite flipping take priority
;over the sprite control bits.  This function modifies the sprite control byte with any flipping
;bits found in ObjectCntrl.

SpriteFlipBitsOveride:
LE038:  lsr ObjectCntrl                 ;Restore MSB.
LE03A:  lda ($00),y                     ;Reload frame data control byte into A.
LE03C:  and #$C0                        ;Extract the two sprite flip bytes from theoriginal-->
LE03E:  ora ObjectCntrl                 ;control byte and set any additional bits from ObjectCntrl.
LE040:  sta $05                         ;Store modified byte to load in sprite control byte later.
LE042:  lda ObjectCntrl                 ;
LE044:  ora #$80                        ;
LE046:  sta ObjectCntrl                 ;Ensure MSB of object control byte remains set.
LE048:  rts                             ;

;--------------------------------[ Explosion placement data ]---------------------------------------

;The following table has the index values into the table after it for finding the placement data
;for an exploding object.

ExplodeIndexTbl:
LE049:  .byte $00, $18, $30

;The following table is used to produce the arcing motion of exploding objects.  It is displacement
;data for the y directions only.  The x displacement is constant.

ExplodePlacementTbl:

;Bottom sprites.
LE04C:  .byte $FC, $F8, $F4, $F0, $EE, $EC, $EA, $E8, $E7, $E6, $E6, $E5, $E5, $E4, $E4, $E3
LE05C:  .byte $E5, $E7, $E9, $EB, $EF, $F3, $F7, $FB

;Middle sprites.
LE064:  .byte $FE, $FC, $FA, $F8, $F6, $F4, $F2, $F0, $EE, $ED, $EB, $EA, $E9, $E8, $E7, $E6
LE074:  .byte $E6, $E6, $E6, $E6, $E8, $EA, $EC, $EE

;Top sprites.
LE07C:  .byte $FE, $FC, $FA, $F8, $F7, $F6, $F5, $F4, $F3, $F2, $F1, $F1, $F0, $F0, $EF, $EF
LE08C:  .byte $EF, $EF, $EF, $EF, $F0, $F0, $F1, $F2

;--------------------------------------[ Update enemy animation ]-----------------------------------

;Advance to next frame of enemy's animation. Basically the same as UpdateObjAnim, only for enemies.

UpdateEnemyAnim:
LE094:  ldx PageIndex                   ;Load index to desired enemy.
LE096:  ldy EnStatus,x                  ;
LE099:  cpy #$05                        ;Is enemy in the process of dying?-->
LE09B:  beq +++                         ;If so, branch to exit.
LE09D:  ldy EnAnimDelay,x               ;
LE0A0:  beq +                           ;Check if current anumation frame is ready to be updated.
LE0A2:  dec EnAnimDelay,x               ;Not ready to update. decrement delay timer and-->
LE0A5:  bne +++                         ;branch to exit.
LE0A7:* sta EnAnimDelay,x               ;Save new animation delay value.
LE0AA:  ldy EnAnimIndex,x               ;Load enemy animation index.
LE0AD:* lda (EnemyAnimPtr),y            ;Get animation data.
LE0AF:  cmp #$FF                        ;End of animation?
LE0B1:  beq ++                          ;If so, branch to reset animation.
LE0B3:  sta EnAnimFrame,x               ;Store current animation frame data.
LE0B6:  iny                             ;Increment to next animation data index.
LE0B7:  tya                             ;
LE0B8:  sta EnAnimIndex,x               ;Save new animation index.
LE0BB:* rts                             ;

LE0BC:* ldy EnResetAnimIndex,x          ;reset animation index.
LE0BF:  bcs ---                         ;Branch always.

;---------------------------------------[ Display status bar ]---------------------------------------

;Displays Samus' status bar components.

DisplayBar:
LE0C1:  ldy #$00                        ;Reset data index.
LE0C3:  lda SpritePagePos               ;Load current sprite index.
LE0C5:  pha                             ;save sprite page pos.
LE0C6:  tax                             ;
LE0C7:* lda DataDisplayTbl,y            ;
LE0CA:  sta Sprite00RAM,x               ;Stor contents of DataDisplayTbl in sprite RAM.
LE0CD:  inx                             ;
LE0CE:  iny                             ;
LE0CF:  cpy #$28                        ;10*4. At end of DataDisplayTbl? If not, loop to-->
LE0D1:  bne -                           ;load next byte from table.

;Display 2-digit health count.
LE0D3:  stx SpritePagePos               ;Save new location in sprite RAM.
LE0D5:  pla                             ;Restore initial sprite page pos.
LE0D6:  tax                             ;
LE0D7:  lda HealthHi                    ;
LE0DA:  and #$0F                        ;Extract upper health digit.
LE0DC:  jsr SPRWriteDigit               ;($E173)Display digit on screen.
LE0DF:  lda HealthLo                    ;
LE0E2:  jsr Adiv16                      ;($C2BF)Move lower health digit to 4 LSBs.
LE0E5:  jsr SPRWriteDigit               ;($E173)Display digit on screen.
LE0E8:  ldy EndTimerHi                  ;
LE0EB:  iny                             ;Is Samus in escape sequence?-->
LE0EC:  bne ++                          ;If so, branch.
LE0EE:  ldy MaxMissiles                 ;
LE0F1:  beq +                           ;Don't show missile count if Samus has no missile containers.

;Display 3-digit missile count.
LE0F3:  lda MissileCount                ;
LE0F6:  jsr HexToDec                    ;($E198)Convert missile hex count to decimal cout.
LE0F9:  lda $02                         ;Upper digit.
LE0FB:  jsr SPRWriteDigit               ;($E173)Display digit on screen.
LE0FE:  lda $01                         ;Middle digit.
LE100:  jsr SPRWriteDigit               ;($E173)Display digit on screen.
LE103:  lda $00                         ;Lower digit.
LE105:  jsr SPRWriteDigit               ;($E173)Display digit on screen.
LE108:  bne +++                         ;Branch always.

;Samus has no missiles, erase missile sprite.
LE10A:* lda #$FF                        ;"Blank" tile.
LE10C:  cpx #$F4                        ;If at last 3 sprites, branch to skip.
LE10E:  bcs ++                          ;
LE110:  sta Sprite03RAM+1,x             ;Erase left half of missile.
LE113:  cpx #$F0                        ;If at last 4 sprites, branch to skip.
LE115:  bcs ++                          ;
LE117:  sta Sprite04RAM+1,x             ;Erase right half of missile.
LE11A:  bne ++                          ;Branch always.

;Display 3-digit end sequence timer.
LE11C:* lda EndTimerHi                  ;
LE11F:  jsr Adiv16                      ;($C2BF)Upper timer digit.
LE122:  jsr SPRWriteDigit               ;($E173)Display digit on screen.
LE125:  lda EndTimerHi                  ;
LE128:  and #$0F                        ;Middle timer digit.
LE12A:  jsr SPRWriteDigit               ;($E173)Display digit on screen.
LE12D:  lda EndTimerLo                  ;
LE130:  jsr Adiv16                      ;($C2BF)Lower timer digit.
LE133:  jsr SPRWriteDigit               ;($E173)Display digit on screen.
LE136:  lda #$58                        ;"TI" sprite(left half of "TIME").
LE138:  sta Sprite00RAM+1,x             ;
LE13B:  inc Sprite00RAM+2,x             ;Change color of sprite.
LE13E:  cpx #$FC                        ;If at last sprite, branch to skip.
LE140:  bcs +                           ;
LE142:  lda #$59                        ;"ME" sprite(right half of "TIME").
LE144:  sta Sprite01RAM+1,x             ;
LE147:  inc Sprite01RAM+2,x             ;Change color of sprite.

LE14A:* ldx SpritePagePos               ;Restore initial sprite page pos.
LE14C:  lda TankCount                   ;
LE14F:  beq ++                          ;Branch to exit if Samus has no energy tanks.

;Display full/empty energy tanks.
LE151:  sta $03                         ;Temp store tank count.
LE153:  lda #$40                        ;X coord of right-most energy tank.
LE155:  sta $00                         ;Energy tanks are drawn from right to left.
LE157:  ldy #$6F                        ;"Full energy tank" tile.
LE159:  lda HealthHi                    ;
LE15C:  jsr Adiv16                      ;($C2BF)/16. A contains # of full energy tanks.
LE15F:  sta $01                         ;Storage of full tanks.
LE161:  bne AddTanks                    ;Branch if at least 1 tank is full.
LE163:  dey                             ;Else switch to "empty energy tank" tile.

AddTanks:
LE164:  jsr AddOneTank                  ;($E17B)Add energy tank to display.
LE167:  dec $01                         ;Any more full energy tanks left?-->
LE169:  bne +                           ;If so, then branch.-->
LE16B:  dey                             ;Otherwise, switch to "empty energy tank" tile.
LE16C:* dec $03                         ;done all tanks?-->
LE16E:  bne AddTanks                    ;if not, loop to do another.

LE170:  stx SpritePagePos               ;Store new sprite page position.
LE172:* rts                             ;

;----------------------------------------[Sprite write digit ]---------------------------------------

;A=value in range 0..9. #$A0 is added to A(the number sprites begin at $A0), and the result is stored
;as the tile # for the sprite indexed by X.

SPRWriteDigit:
LE173:  ora #$A0                        ;#$A0 is index into pattern table for numbers.
LE175:  sta Sprite00RAM+1,x             ;Store proper nametable pattern in sprite RAM.
LE178:  jmp Xplus4                      ;Find next sprite pattern table byte.

;----------------------------------[ Add energy tank to display ]------------------------------------

;Add energy tank to Samus' data display.

AddOneTank:
LE17B:  lda #$17                        ;Y coord-1.
LE17D:  sta Sprite00RAM,x               ;
LE180:  tya                             ;Tile value.
LE181:  sta Sprite00RAM+1,x             ;
LE184:  lda #$01                        ;Palette #.
LE186:  sta Sprite00RAM+2,x             ;
LE189:  lda $00                         ;X coord.
LE18B:  sta Sprite00RAM+3,x             ;
LE18E:  sec                             ;
LE18F:  sbc #$0A                        ;Find x coord of next energy tank.
LE191:  sta $00                         ;

;-----------------------------------------[ Add 4 to x ]---------------------------------------------

Xplus4:
LE193:  inx                             ;
LE194:  inx                             ;
LE195:  inx                             ;Add 4 to value stored in X.
LE196:  inx                             ;
LE197:  rts                             ;

;------------------------------------[ Convert hex to decimal ]--------------------------------------

;Convert 8-bit value in A to 3 decimal digits. Upper digit put in $02, middle in $01 and lower in $00.

HexToDec:
LE198:  ldy #100                        ;Find upper digit.
LE19A:  sty $0A                         ;
LE19C:  jsr GetDigit                    ;($E1AD)Extract hundreds digit.
LE19F:  sty $02                         ;Store upper digit in $02.
LE1A1:  ldy #10                         ;Find middle digit.
LE1A3:  sty $0A                         ;
LE1A5:  jsr GetDigit                    ;($E1AD)Extract tens digit.
LE1A8:  sty $01                         ;Store middle digit in $01.
LE1AA:  sta $00                         ;Store lower digit in $00
LE1AC:  rts                             ;

GetDigit:
LE1AD:  ldy #$00                        ;
LE1AF:  sec                             ;
LE1B0:* iny                             ;
LE1B1:  sbc $0A                         ;Loop and subtract value in $0A from A until carry flag-->
LE1B3:  bcs -                           ;is not set.  The resulting number of loops is the decimal-->
LE1B5:  dey                             ;number extracted and A is the remainder.
LE1B6:  adc $0A                         ;
LE1B8:  rts                             ;

;-------------------------------------[ Status bar sprite data ]-------------------------------------

;Sprite data for Samus' data display

DataDisplayTbl:
LE1B9:  .byte $21,$A0,$01,$30           ;Upper health digit.
LE1BD:  .byte $21,$A0,$01,$38           ;Lower health digit.
LE1C1:  .byte $2B,$FF,$01,$28           ;Upper missile digit.
LE1C5:  .byte $2B,$FF,$01,$30           ;Middle missile digit.
LE1C9:  .byte $2B,$FF,$01,$38           ;Lower missile digit.
LE1CD:  .byte $2B,$5E,$00,$18           ;Left half of missile.
LE1D1:  .byte $2B,$5F,$00,$20           ;Right half of missile.
LE1D5:  .byte $21,$76,$01,$18           ;E
LE1D9:  .byte $21,$7F,$01,$20           ;N
LE1DD:  .byte $21,$3A,$00,$28           ;..

;-------------------------------------------[ Bit scan ]---------------------------------------------

;This function takes the value stored in A and right shifts it until a set bit is encountered.
;Once a set bit is encountered, the function exits and returns the bit number of the set bit.
;The returned value is stored in A. 

BitScan:
LE1E1:  stx $0E                         ;Save X.
LE1E3:  ldx #$00                        ;First bit is bit 0.
LE1E5:* lsr                             ;Transfer bit to carry flag.
LE1E6:  bcs +                           ;If the shifted bit was 1, Branch out of loop.
LE1E8:  inx                             ;Increment X to keep of # of bits checked.
LE1E9:  cpx #$08                        ;Have all 8 bit been tested?-->
LE1EB:  bne -                           ;If not, branch to check the next bit.
LE1ED:* txa                             ;Return which bit number was set.
LE1EE:  ldx $0E                         ;Restore X.
LE1F0:* rts                             ;

;------------------------------------------[ Scroll door ]-------------------------------------------

;Scrolls the screen if Samus is inside a door.

ScrollDoor:
LE1F1:  ldx DoorStatus                  ;
LE1F3:  beq -                           ;Exit if Samus isn't in a door.
LE1F5:  dex                             ;
LE1F6:  bne +                           ;Not in right door. branch to check left door.
LE1F8:  jsr ScrollRight                 ;($E6D2)DoorStatus=1, scroll 1 pixel right.
LE1FB:  jmp ++                          ;Jump to check if door scroll is finished.

LE1FE:* dex                             ;Check if in left door.
LE1FF:  bne ++                          ;
LE201:  jsr ScrollLeft                  ;($E6A7)DoorStatus=2, scroll 1 pixel left.
LE204:* ldx ScrollX                     ;Has x scroll offset reached 0?-->
LE206:  bne Exit15                      ;If not, branch to exit.

;Scrolled one full screen, time to exit door.
LE208:  ldx #$05                        ;Samus is exiting the door.
LE20A:  bne DoOneDoorScroll             ;Branch always.

LE20C:* dex                             ;
LE20D:  bne +                           ;Check if need to scroll down to center door.
LE20F:  jsr ScrollDown                  ;($E519)DoorStatus=3, scroll 1 pixel down.
LE212:  jmp ++                          ;Jump to check y scrolling value.
LE215:* dex                             ;
LE216:  bne Exit15                      ;Check if need to scroll up to center door.
LE218:  jsr ScrollUp                    ;($E4F1)DoorStatus=4, scroll 1 pixel up.

VerticalRoomCentered:
LE21B:* ldx ScrollY                     ;Has room been centered on screen?-->
LE21D:  bne Exit15                      ;If not, branch to exit.
LE21F:  stx DoorOnNameTable3            ;
LE221:  stx DoorOnNameTable0            ;Erase door nametable data.
LE223:  inx                             ;X=1.
LE224:  lda ObjectX                     ;Did Samus enter in the right hand door?-->
LE227:  bmi ++                          ;If so, branch.
LE229:  inx                             ;X=2. Samus is in left door.
LE22A:  bne ++                          ;Branch always.

;This function is called once after door scrolling is complete.

DoOneDoorScroll:
LE22C:  lda #$20                        ;Set DoorDelay to 32 frames(comming out of door).
LE22E:  sta DoorDelay                   ;
LE230:  lda SamusDoorData               ;Check if scrolling should be toggled.
LE232:  jsr Amul8                       ;($C2C6)*8. Is door not to toggle scrolling(item room,-->
LE235:  bcs +                           ;bridge room, etc.)? If so, branch to NOT toggle scrolling.
LE237:  ldy DoorScrollStatus            ;If comming from vertical shaft, skip ToggleScroll because-->
LE239:  cpy #$03                        ;the scroll was already toggled after room was centered-->
LE23B:  bcc ++                          ;by the routine just above.
LE23D:* lda #$47                        ;Set mirroring for vertical mirroring(horz scrolling).
LE23F:  bne ++                          ;Branch always.

LE241:* jsr ToggleScroll                ;($E252)Toggle scrolling and mirroring.
LE244:* sta MirrorCntrl                 ;Store new mirror control data.
LE246:  stx DoorStatus                  ;DoorStatus=5. Done with door scrolling.

Exit15:
LE248:  rts                             ;Exit for several routines above.

;------------------------------------[ Toggle Samus nametable ]--------------------------------------

ToggleSamusHi:
LE249:  lda ObjectHi                    ;
LE24C:  eor #$01                        ;Change Samus' current nametable from one to the other.
LE24E:  sta ObjectHi                    ;
LE251:  rts                             ;

;-------------------------------------------[ Toggle scroll ]----------------------------------------

;Toggles both mirroring and scroll direction when Samus has moved from
;a horizontal shaft to a vertical shaft or vice versa.

ToggleScroll:
LE252:  lda ScrollDir                   ;
LE254:  eor #$03                        ;Toggle scroll direction.
LE256:  sta ScrollDir                   ;
LE258:  lda MirrorCntrl                 ;Toggle mirroring.
LE25A:  eor #$08                        ;
LE25C:  rts                             ;

;----------------------------------------[ Is Samus in lava ]----------------------------------------

;The following function checks to see if Samus is in lava.  If she is, the carry bit is cleared,
;if she is not, the carry bit is set. Samus can only be in lava if in a horizontally scrolling
;room. If Samus is 24 pixels or less away from the bottom of the screen, she is considered to be
;in lava whether its actually there or not.

IsSamusInLava:
LE25D:  lda #$01                        ;
LE25F:  cmp ScrollDir                   ;Set carry bit(and exit) if scrolling up or down.
LE261:  bcs +                           ;
LE263:  lda #$D8                        ;If Samus is Scrolling left or right and within 24 pixels-->
LE265:  cmp ObjectY                     ;of the bottom of the screen, she is in lava. Clear carry bit.
LE268:* rts                             ;

;----------------------------------[ Check lava and movement routines ]------------------------------

LavaAndMoveCheck:
LE269:  lda ObjAction                   ;
LE26C:  cmp #sa_Elevator                ;Is Samus on elevator?-->
LE26E:  beq +                           ;If so, branch.
LE270:  cmp #sa_Dead                    ;Is Samus Dead-->
LE272:  bcs -                           ;If so, branch to exit.
LE274:* jsr IsSamusInLava               ;($E25D)Clear carry flag if Samus is in lava.
LE277:  ldy #$FF                        ;Assume Samus not in lava.
LE279:  bcs ++++                        ;Samus not in lava so branch.

;Samus is in lava.
LE27B:  sty DamagePushDirection         ;Don't push Samus from lava damage.
LE27D:  jsr ClearHealthChange           ;($F323)Clear any pending health changes to Samus.
LE280:  lda #$32                        ;
LE282:  sta SamusBlink                  ;Make Samus blink.
LE284:  lda FrameCount                  ;
LE286:  and #$03                        ;Start the jump SFX every 4th frame while in lava.
LE288:  bne +                           ;
LE28A:  jsr SFX_SamusJump               ;($CBAC)Initiate jump SFX.
LE28D:* lda FrameCount                  ;
LE28F:  lsr                             ;This portion of the code causes Samus to be damaged by-->
LE290:  and #$03                        ;lava twice every 8 frames if she does not have the varia-->
LE292:  bne ++                          ;but only once every 8 frames if she does.
LE294:  lda SamusGear                   ;
LE297:  and #gr_VARIA                   ;Does Samus have the Varia?-->
LE299:  beq +                           ;If not, branch.
LE29B:  bcc ++                          ;Samus has varia. Carry set every other frame. Half damage.
LE29D:* lda #$07                        ;
LE29F:  sta HealthLoChange              ;Samus takes lava damage.
LE2A1:  jsr SubtractHealth              ;($CE92)
LE2A4:* ldy #$00                        ;Prepare to indicate Samus is in lava.
LE2A6:* iny                             ;Set Samus lava status.
LE2A7:  sty SamusInLava                 ;

SamusMoveVertically:
LE2A9:  jsr VertAccelerate              ;($E37A)Calculate vertical acceleration.
LE2AC:  lda ObjectY                     ;
LE2AF:  sec                             ;
LE2B0:  sbc ScrollY                     ;Calculate Samus' screen y position.
LE2B2:  sta SamusScrY                   ;
LE2B4:  lda $00                         ;Load temp copy of vertical speed.
LE2B6:  bpl ++++                        ;If Samus is moving downwards, branch.

LE2B8:  jsr TwosCompliment              ;($C3D4)Get twos compliment of vertical speed.
LE2BB:  ldy SamusInLava                 ;Is Samus in lava?
LE2BD:  beq +                           ;If not, branch,-->
LE2BF:  lsr                             ;else cut vertical speed in half.
LE2C0:  beq SamusMoveHorizontally       ;($E31A)Branch if no vertical mvmnt to Check left/right mvmnt.

;Samus is moving upwards.
LE2C2:* sta ObjectCounter               ;Store number of pixels to move Samus this frame.
LE2C4:* jsr MoveSamusUp                 ;($E457)Attempt to move Samus up 1 pixel.
LE2C7:  bcs +                           ;Branch if Samus successfully moved up 1 pixel.

LE2C9:  sec                             ;Samus blocked upwards. Divide her speed by 2 and set the
LE2CA:  ror ObjVertSpeed                ;MSB to reverse her direction of travel.
LE2CD:  ror VertCntrLinear              ;
LE2D0:  jmp SamusMoveHorizontally       ;($E31A)Attempt to move Samus left/right.

LE2D3:* dec ObjectCounter               ;1 pixel movement is complete.
LE2D5:  bne --                          ;Branch if Samus needs to be moved another pixel.

;Samus is moving downwards.
LE2D7:* beq SamusMoveHorizontally       ;($E31A)Branch if no vertical mvmnt to Check left/right mvmnt.
LE2D9:  ldy SamusInLava                 ;Is Samus in lava?
LE2DB:  beq +                           ;If not, branch,-->
LE2DD:  lsr                             ;Else reduce Samus speed by 75%(divide by 4).
LE2DE:  lsr                             ;
LE2DF:  beq SamusMoveHorizontally       ;($E31A)Attempt to move Samus left/right.

LE2E1:* sta ObjectCounter               ;Store number of pixels to move Samus this frame.
LE2E3:* jsr MoveSamusDown               ;($E4A3)Attempt to move Samus 1 pixel down.
LE2E6:  bcs +++                         ;Branch if Samus successfully moved down 1 pixel.

;Samus bounce after hitting the ground in ball form.
LE2E8:  lda ObjAction                   ;
LE2EB:  cmp #sa_Roll                    ;Is Samus rolled into a ball?-->
LE2ED:  bne +                           ;If not, branch.
LE2EF:  lsr ObjVertSpeed                ;Divide verticle speed by 2.
LE2F2:  beq ++                          ;Speed not fast enough to bounce. branch to skip.
LE2F4:  ror VertCntrLinear              ;Move carry bit into MSB to reverse Linear counter.
LE2F7:  lda #$00                        ;
LE2F9:  sec                             ;
LE2FA:  sbc VertCntrLinear              ;Subtract linear counter from 0 and save the results.-->
LE2FD:  sta VertCntrLinear              ;Carry will be cleared.
LE300:  lda #$00                        ;
LE302:  sbc ObjVertSpeed                ;Subtract vertical speed from 0. this will reverse the-->
LE305:  sta ObjVertSpeed                ;vertical direction of travel(bounce up).
LE308:  jmp SamusMoveHorizontally       ;($E31A)Attempt to move Samus left/right.

;Samus has hit the ground after moving downwards. 
LE30B:* jsr SFX_SamusWalk               ;($CB96)Play walk SFX.
LE30E:* jsr StopVertMovement            ;($D147)Clear vertical movement data.
LE311:  sty SamusGravity                ;Clear Samus gravity value.
LE314:  beq SamusMoveHorizontally       ;($E31A)Attempt to move Samus left/right.

LE316:* dec ObjectCounter               ;1 pixel movement is complete.
LE318:  bne ----                        ;Branch if Samus needs to be moved another pixel.

SamusMoveHorizontally:
LE31A:  jsr HorzAccelerate              ;($E3E5)Horizontally accelerate Samus.
LE31D:  lda ObjectX                     ;
LE320:  sec                             ;Calculate Samus' x position on screen.
LE321:  sbc ScrollX                     ;
LE323:  sta SamusScrX                   ;Save Samus' x position.
LE325:  lda $00                         ;Load Samus' current horizontal speed.
LE327:  bpl +++                         ;Branch if moving right.

;Samus is moving left.
LE329:  jsr TwosCompliment              ;($C3D4)Get twos compliment of horizontal speed.
LE32C:  ldy SamusInLava                 ;Is Samus in lava?-->
LE32E:  beq +                           ;If not, branch,-->
LE330:  lsr                             ;else cut horizontal speed in half.
LE331:  beq Exit10                      ;Branch to exit if Samus not going to move this frame.

LE333:* sta ObjectCounter               ;Store number of pixels to move Samus this frame.
LE335:* jsr MoveSamusLeft               ;($E626)Attempt to move Samus 1 pixel to the left.
LE338:  jsr CheckStopHorzMvmt           ;($E365)Check if horizontal movement needs to be stopped.
LE33B:  dec ObjectCounter               ;1 pixel movement is complete.
LE33D:  bne -                           ;Branch if Samus needs to be moved another pixel.

LE33F:  lda SamusDoorData               ;Has Samus entered a door?-->
LE341:  beq Exit10                      ;If not, branch to exit.
LE343:  lda #$01                        ;Door leads to the left.
LE345:  bne ++++                        ;Branch always.

;Samus is moving right.
LE347:* beq Exit10                      ;Branch to exit if Samus not moving horizontally.
LE349:  ldy SamusInLava                 ;Is Samus in lava?-->
LE34B:  beq +                           ;If not, branch,-->
LE34D:  lsr                             ;else cut horizontal speed in half.
LE34E:  beq Exit10                      ;Branch to exit if Samus not going to move this frame.

LE350:* sta ObjectCounter               ;Store number of pixels to move Samus this frame.
LE352:* jsr MoveSamusRight              ;($E668)Attempt to move Samus 1 pixel to the right.
LE355:  jsr CheckStopHorzMvmt           ;($E365)Check if horizontal movement needs to be stopped.
LE358:  dec ObjectCounter               ;1 pixel movement is complete.
LE35A:  bne -                           ;Branch if Samus needs to be moved another pixel.

LE35C:  lda SamusDoorData               ;Has Samus entered a door?-->
LE35E:  beq Exit10                      ;If not, branch to exit.
LE360:  lda #$00                        ;
LE362:* sta SamusDoorDir                ;Door leads to the right.

Exit10:
LE364:  rts                             ;Exit for routines above and below.

CheckStopHorzMvmt:
LE365:  bcs Exit10                      ;Samus moved successfully. Branch to exit.
LE367:  lda #$01                        ;Load counter with #$01 so this function will not be-->
LE369:  sta ObjectCounter               ;called again.
LE36C:  lda SamusGravity                ;Is Samus on the ground?-->
LE36E:  bne Exit10                      ;If not, branch to exit.
LE370:  lda ObjAction                   ;
LE373:  cmp #sa_Roll                    ;Is Samus rolled into a ball?-->
LE375:  beq Exit10                      ;If so, branch to exit.
LE377:  jmp StopHorzMovement            ;($CF55)Stop horizontal movement or play walk SFX if stopped.

;-------------------------------------[ Samus vertical acceleration ]--------------------------------

;The following code accelerates/decelerates Samus vertically.  There are 4 possible values for
;gravity used in the acceleration calculation. The higher the number, the more intense the gravity.
;The possible values for gravity are as follows:
;#$38-When Samus has been hit by an enemy.
;#$1A-When Samus is falling.
;#$18-Jump without high jump boots.
;#$12-Jump with high jump boots.

VertAccelerate:
LE37A:  lda SamusGravity                ;Is Samus rising or falling?-->
LE37D:  bne ++                          ;Branch if yes.
LE37F:  lda #$18                        ;
LE381:  sta SamusHorzSpeedMax           ;Set Samus maximum running speed.
LE384:  lda ObjectY                     ;
LE387:  clc                             ;
LE388:  adc ObjRadY                     ;Check is Samus is obstructed downwards on y room-->
LE38B:  and #$07                        ;positions divisible by 8(every 8th pixel).
LE38D:  bne +                           ;
LE38F:  jsr CheckMoveDown               ;($E7AD)Is Samus obstructed downwards?-->
LE392:  bcc ++                          ;Branch if yes.
LE394:* jsr SamusOnElevatorOrEnemy      ;($D976)Calculate if Samus standing on elevator or enemy.
LE397:  lda SamusOnElevator             ;Is Samus on an elevator?-->
LE39A:  bne +                           ;Branch if yes.
LE39C:  lda OnFrozenEnemy               ;Is Samus standing on a frozen enemy?-->
LE39E:  bne +                           ;Branch if yes.
LE3A0:  lda #$1A                        ;Samus is falling. Store falling gravity value.
LE3A2:  sta SamusGravity                ;

LE3A5:* ldx #$05                        ;Load X with maximum downward speed.
LE3A7:  lda VertCntrLinear              ;
LE3AA:  clc                             ;The higher the gravity, the faster this addition overflows-->
LE3AB:  adc SamusGravity                ;and the faster ObjVertSpeed is incremented.
LE3AE:  sta VertCntrLinear              ;
LE3B1:  lda ObjVertSpeed                ;Every time above addition sets carry bit, ObjVertSpeed is-->
LE3B4:  adc #$00                        ;incremented. This has the effect of speeding up a fall-->
LE3B6:  sta ObjVertSpeed                ;and slowing down a jump.
LE3B9:  bpl +                           ;Branch if Samus is moving downwards.

;Check if maximum upward speed has been exceeded. If so, prepare to set maximum speed.
LE3BB:  lda #$00                        ;
LE3BD:  cmp VertCntrLinear              ;Sets carry bit.
LE3C0:  sbc ObjVertSpeed                ;Subtract ObjVertSpeed to see if maximum speed has-->
LE3C3:  cmp #$06                        ;been exceeded.
LE3C5:  ldx #$FA                        ;Load X with maximum upward speed.
LE3C7:  bne ++                          ;Branch always.

;Check if maximum downward speed has been reached. If so, prepare to set maximum speed.
LE3C9:* cmp #$05                        ;Has maximum downward speed been reached?-->
LE3CB:* bcc +                           ;If not, branch.

;Max verticle speed reached or exceeded. Adjust Samus verticle speed to max.
LE3CD:  jsr StopVertMovement            ;($D147)Clear verticle movement data.
LE3D0:  stx ObjVertSpeed                ;Set Samus vertical speed to max.

;This portion of the function creates an exponential increase/decrease in verticle speed. This is the
;part of the function that does all the work to make Samus' jump seem natural.
LE3D3:* lda VertCntrNonLinear           ;
LE3D6:  clc                             ;This function adds itself plus the linear verticle counter-->
LE3D7:  adc VertCntrLinear              ;onto itself every frame.  This causes the non-linear-->
LE3DA:  sta VertCntrNonLinear           ;counter to increase exponentially.  This function will-->
LE3DD:  lda #$00                        ;cause Samus to reach maximum speed first in most-->
LE3DF:  adc ObjVertSpeed                ;situations before the linear counter.
LE3E2:  sta $00                         ;$00 stores temp copy of current verticle speed.
LE3E4:  rts                             ;

;----------------------------------------------------------------------------------------------------

HorzAccelerate:
LE3E5:  lda SamusHorzSpeedMax
        jsr Amul16       ; * 16
        sta $00
        sta $02
        lda SamusHorzSpeedMax
        jsr Adiv16       ; / 16
        sta $01
        sta $03

        lda HorzCntrLinear
        clc
        adc SamusHorzAccel
        sta HorzCntrLinear
        tax
        lda #$00
        bit SamusHorzAccel
        bpl +                           ;Branch if Samus accelerating to the right.

        lda #$FF

*       adc ObjHorzSpeed
        sta ObjHorzSpeed
        tay
        bpl +                           ;Branch if Samus accelerating to the right.

        lda #$00
        sec
        sbc HorzCntrLinear
        tax
        lda #$00
        sbc ObjHorzSpeed
        tay
        jsr LE449

*       cpx $02
        tya
        sbc $03
        bcc +
        lda $00
        sta HorzCntrLinear
        lda $01
        sta ObjHorzSpeed
*       lda HorzCntrNonLinear
        clc
        adc HorzCntrLinear
        sta HorzCntrNonLinear
        lda #$00
        adc ObjHorzSpeed
        sta $00                         ;$00 stores temp copy of current horizontal speed.
        rts                             ;

LE449:  lda #$00
        sec
        sbc $00
        sta $00
        lda #$00
        sbc $01
        sta $01
        rts

;----------------------------------------------------------------------------------------------------

;Attempt to move Samus one pixel up.

MoveSamusUp:
LE457:  lda ObjectY                     ;Get Samus' y position in room.
        sec                             ;
        sbc ObjRadY                     ;Subtract Samus' vertical radius.
LE45E:  and #$07                        ;Check if result is a multiple of 8. If so, branch to-->
LE460:  bne +                           ;Only call crash detection every 8th pixel.
LE462:  jsr CheckMoveUp                 ;($E7A2)Check if Samus obstructed UPWARDS.-->
        bcc +++++++                     ;If so, branch to exit(can't move any further).
*       lda ObjAction                   ;
        cmp #sa_Elevator                ;Is Samus riding elevator?-->
        beq +                           ;If so, branch.
        jsr SamusOnElevatorOrEnemy      ;($D976)Calculate if Samus standing on elevator or enemy.
        lda SamusHit
        and #$42
        cmp #$42
        clc
        beq ++++++
*       lda SamusScrY
        cmp #$66        ; reached up scroll limit?
        bcs +      ; branch if not
        jsr ScrollUp
        bcc ++
*       dec SamusScrY
*       lda ObjectY
        bne ++
        lda ScrollDir
        and #$02
        bne +
        jsr ToggleSamusHi       ; toggle 9th bit of Samus' Y coord
*       lda #240
        sta ObjectY
*       dec ObjectY
        inc SamusJumpDsplcmnt
        sec
*       rts

; attempt to move Samus one pixel down

MoveSamusDown:
        lda ObjectY
        clc
        adc ObjRadY
        and #$07
        bne +              ; only call crash detection every 8th pixel
        jsr CheckMoveDown       ; check if Samus obstructed DOWNWARDS
        bcc +++++++      ; exit if yes
*       lda ObjAction
        cmp #sa_Elevator        ; is Samus in elevator?
        beq +
        jsr LD976
        lda SamusOnElevator
        clc
        bne ++++++
        lda OnFrozenEnemy
        bne ++++++
*       lda SamusScrY
        cmp #$84        ; reached down scroll limit?
        bcc +      ; branch if not
        jsr ScrollDown
        bcc ++
*       inc SamusScrY
*       lda ObjectY
        cmp #239
        bne ++
        lda ScrollDir
        and #$02
        bne +
        jsr ToggleSamusHi       ; toggle 9th bit of Samus' Y coord
*       lda #$FF
        sta ObjectY
*       inc ObjectY
        dec SamusJumpDsplcmnt
        sec
*       rts

; Attempt to scroll UP

        ScrollUp:
        lda ScrollDir
        beq +
        cmp #$01
        bne ++++
        dec ScrollDir
        lda ScrollY
        beq +
        dec MapPosY
*       ldx ScrollY
        bne +
        dec MapPosY     ; decrement MapY
        jsr GetRoomNum  ; put room # at current map pos in $5A
        bcs ++   ; if function returns CF = 1, moving up is not possible
        jsr LE9B7       ; switch to the opposite Name Table
        ldx #240        ; new Y coord
*       dex
        jmp LE53F

*       inc MapPosY
*       sec
        rts

; Attempt to scroll DOWN

        ScrollDown:
        ldx ScrollDir
        dex
        beq +
        bpl +++++
        inc ScrollDir
        lda ScrollY
        beq +
        inc MapPosY
*       lda ScrollY
        bne +
        inc MapPosY     ; increment MapY
        jsr GetRoomNum  ; put room # at current map pos in $5A
        bcs +++   ; if function returns CF = 1, moving down is not possible
*       ldx ScrollY
        cpx #239
        bne +
        jsr LE9B7       ; switch to the opposite Name Table
        ldx #$FF
*       inx
LE53F:  stx ScrollY
        jsr LE54A       ; check if it's time to update Name Table
        clc
        rts

*       dec MapPosY
*       sec
*       rts

LE54A:  jsr SetupRoom
        ldx RoomNumber
        inx
        bne -
        lda ScrollDir
        and #$02
        bne +
        jmp LE571
*       jmp LE701

; Table

Table11:
        .byte $07
        .byte $00

;---------------------------------[ Get PPU and RoomRAM addresses ]----------------------------------

PPUAddrs:
LE560:  .byte $20                       ;High byte of nametable #0(PPU).
LE561:  .byte $2C                       ;High byte of nametable #3(PPU)

WRAMAddrs:
LE562:  .byte $60                       ;High byte of RoomRAMA(cart RAM).
LE563:  .byte $64                       ;High byte of RoomRAMB(cart RAM).

GetNameAddrs:
LE564:  jsr GetNameTable                ;($EB85)Get current name table number.
LE567:  and #$01                        ;Update name table 0 or 3.
LE569:  tay                             ;
LE56A:  lda PPUAddrs,y                  ;Get high PPU addr of nametable(dest).
LE56D:  ldx WRAMAddrs,y                 ;Get high cart RAM addr of nametable(src).
LE570:  rts                             ;

;----------------------------------------------------------------------------------------------------

; check if it's time to update nametable (when scrolling is VERTICAL)

LE571:  ldx ScrollDir
        lda ScrollY
        and #$07        ; compare value = 0 if ScrollDir = down, else 7
        cmp Table11,x
        bne --     ; exit if not equal (no nametable update)

LE57C:  ldx ScrollDir                   ;
        cpx TempScrollDir               ;Still scrolling same direction when room was loaded?-->
        bne --                          ;If not, branch to exit.
        lda ScrollY
        and #$F8        ; keep upper 5 bits
        sta $00
        lda #$00
        asl $00
        rol
        asl $00
        rol

LE590:  sta $01  ; $0001 = (ScrollY & 0xF8) << 2 = row offset
        jsr GetNameAddrs
        ora $01
        sta $03
        txa
        ora $01
        sta $01
        lda $00
        sta $02
        lda ScrollDir
        lsr             ; A = 0 if vertical scrolling, 1 if horizontal
        tax
        lda Table01,x
        sta $04
        ldy #$01
        sty PPUDataPending      ; data pending = YES
        dey
        ldx PPUStrIndex
        lda $03
        jsr WritePPUByte                ;($C36B)Put data byte into PPUDataString.
        lda $02
        jsr WritePPUByte
        lda $04
        jsr SeparateControlBits         ;($C3C6)
*       lda ($00),y
        jsr WritePPUByte
        sty $06
        ldy #$01        ; WRAM pointer increment = 1...
        bit $04  ; ... if bit 7 (PPU inc) of $04 clear
        bpl +
        ldy #$20        ; else ptr inc = 32
*       jsr AddYToPtr00                 ;($C2A8)
        ldy $06
        dec $05
        bne --
        stx PPUStrIndex
        jsr EndPPUString

Table01:
        .byte $20                       ;Horizontal write. PPU inc = 1, length = 32 tiles.
        .byte $9E                       ;Vertical write... PPU inc = 32, length = 30 tiles.

;---------------------------------[Write PPU attribute table data ]----------------------------------

WritePPUAttribTbl:
LE5E2:  ldx #$C0                        ;Low byte of First row of attribute table.
LE5E4:  lda RoomNumber                  ;
LE5E6:  cmp #$F2                        ;Is this the second pass through the routine?-->
LE5E8:  beq +                           ;If so, branch.
LE5EA:  ldx #$E0                        ;Low byte of second row of attribute table.
LE5EC:* stx $00                         ;$0000=RoomRAM atrrib table starting address.
LE5EE:  stx $02                         ;$0002=PPU attrib table starting address.
LE5F0:  jsr GetNameAddrs                ;($E564)Get name table addr and corresponding RoomRAM addr.
LE5F3:  ora #$03                        ;#$23 for attrib table 0, #$2F for attrib table 3.
LE5F5:  sta $03                         ;Store results.
LE5F7:  txa                             ;move high byte of RoomRAM to A.
LE5F8:  ora #$03                        ;#$63 for RoomRAMA, #$67 for RoomRAMB(Attrib tables).
LE5FA:  sta $01                         ;Store results.
LE5FC:  lda #$01                        ;
LE5FE:  sta PPUDataPending              ;Data pending = YES.
LE600:  ldx PPUStrIndex                 ;Load current index into PPU strng to append data.
LE603:  lda $03                         ;Store high byte of starting address(attrib table).
LE605:  jsr WritePPUByte                ;($C36B)Put data byte into PPUDataString.
LE608:  lda $02                         ;Store low byte of starting address(attrib table).
LE60A:  jsr WritePPUByte                ;($C36B)Put data byte into PPUDataString.
LE60D:  lda #$20                        ;Length of data to write(1 row of attrib data).
LE60F:  sta $04                         ;
LE611:  jsr WritePPUByte                ;($C36B)Write control byte. Horizontal write.
LE614:  ldy #$00                        ;Reset index into data string.
LE616:* lda ($00),y                     ;Get data byte.
LE618:  jsr WritePPUByte                ;($C36B)Put data byte into PPUDataString.
LE61B:  iny                             ;Increment to next attrib data byte.
LE61C:  dec $04                         ;
LE61E:  bne -                           ;Loop until all attrib data loaded into PPU.
LE620:  stx PPUStrIndex                 ;Store updated PPU string index.
LE623:  jsr EndPPUString                ;($C376)Append end marker(#$00) and exit writing routines.

;----------------------------------------------------------------------------------------------------

; attempt to move Samus one pixel left

MoveSamusLeft:
LE626:  lda ObjectX
        sec
        sbc ObjRadX
        and #$07
        bne +              ; only call crash detection every 8th pixel
        jsr CheckMoveLeft       ; check if player is obstructed to the LEFT
        bcc +++++        ; branch if yes! (CF = 0)
*       jsr LD976
        lda SamusHit
        and #$41
        cmp #$41
        clc
        beq ++++
        lda SamusScrX
        cmp #$71        ; reached left scroll limit?
        bcs +      ; branch if not
        jsr ScrollLeft
        bcc ++
*       dec SamusScrX
*       lda ObjectX
        bne +
        lda ScrollDir
        and #$02
        beq +
        jsr ToggleSamusHi       ; toggle 9th bit of Samus' X coord
*       dec ObjectX
        sec
        rts

; crash with object on the left

*       lda #$00
        sta SamusDoorData
        rts

; attempt to move Samus one pixel right

MoveSamusRight:
        lda ObjectX
        clc
        adc ObjRadX
        and #$07
        bne +              ; only call crash detection every 8th pixel
        jsr CheckMoveRight      ; check if Samus is obstructed to the RIGHT
        bcc +++++       ; branch if yes! (CF = 0)
*       jsr LD976
        lda SamusHit
        and #$41
        cmp #$40
        clc
        beq ++++
        lda SamusScrX
        cmp #$8F        ; reached right scroll limit?
        bcc +      ; branch if not
        jsr ScrollRight
        bcc ++
*       inc SamusScrX
*       inc ObjectX      ; go right, Samus!
        bne +
        lda ScrollDir
        and #$02
        beq +
        jsr ToggleSamusHi       ; toggle 9th bit of Samus' X coord
*       sec
        rts

; crash with object on the right

*       lda #$00
        sta SamusDoorData
        rts

; Attempt to scroll LEFT

        ScrollLeft:
        lda ScrollDir
        cmp #$02
        beq +
        cmp #$03
        bne ++++
        dec ScrollDir
        lda ScrollX
        beq +
        dec MapPosX
*       lda ScrollX
        bne +
        dec MapPosX     ; decrement MapX
        jsr GetRoomNum  ; put room # at current map pos in $5A
        bcs ++  ; if function returns CF=1, scrolling left is not possible
        jsr LE9B7       ; switch to the opposite Name Table
*       dec ScrollX
        jsr LE54A       ; check if it's time to update Name Table
        clc
        rts

*       inc MapPosX
*       sec
        rts

; Attempt to scroll RIGHT

ScrollRight:
        lda ScrollDir
        cmp #$03
        beq +
        cmp #$02
        bne +++++
        inc ScrollDir
        lda ScrollX
        beq +
        inc MapPosX
*       lda ScrollX
        bne +
        inc MapPosX
        jsr GetRoomNum  ; put room # at current map pos in $5A
        bcs +++   ; if function returns CF=1, scrolling right is not possible
*       inc ScrollX
        bne +
        jsr LE9B7       ; switch to the opposite Name Table
*       jsr LE54A       ; check if it's time to update Name Table
        clc
        rts

*       dec MapPosX
*       sec
*       rts

Table02:
        .byte $07,$00

; check if it's time to update nametable (when scrolling is HORIZONTAL)

LE701:  ldx ScrollDir
        lda ScrollX
        and #$07        ; keep lower 3 bits
        cmp Table02-2,x ; compare value = 0 if ScrollDir = right, else 7
        bne -      ; exit if not equal (no nametable update)

LE70C:  ldx ScrollDir
        cpx TempScrollDir
        bne -
        lda ScrollX
        and #$F8        ; keep upper five bits
        jsr Adiv8       ; / 8 (make 'em lower five)
        sta $00
        lda #$00
        jmp LE590

;---------------------------------------[ Get room number ]-------------------------------------------

;Gets room number at current map position. Sets carry flag if room # at map position is FF.
;If valid room number, the room number is stored in $5A.

GetRoomNum:
LE720:  lda ScrollDir                   ;
LE722:  lsr                             ;Branch if scrolling vertical.
LE723:  beq +                           ;

LE725:  rol                             ;Restore value of a
LE726:  adc #$FF                        ;A=#$01 if scrolling left, A=#$02 if scrolling right.
LE728:  pha                             ;Save A.
LE729:  jsr OnNameTable0                ;($EC93)Y=1 if name table=0, Y=0 if name table=3.
LE72C:  pla                             ;Restore A.
LE72D:  and $006C,y                     ;
LE730:  sec                             ;
LE731:  bne +++++                       ;Can't load room, a door is in the way. This has the-->
                                        ;effect of stopping the scrolling until Samus walks-->
                                        ;through the door(horizontal scrolling only).

LE733:* lda MapPosY                     ;Map pos y.
LE735:  jsr Amul16                      ;($C2C5)Multiply by 16.
LE738:  sta $00                         ;Store multiplied value in $00.
LE73A:  lda #$00                        ;
LE73C:  rol                             ;Save carry, if any.
LE73D:  rol $00                         ;Multiply value in $00 by 2.
LE73F:  rol                             ;Save carry, if any.
LE740:  sta $01                         ;
LE742:  lda $00                         ;
LE744:  adc MapPosX                     ;Add map pos X to A.
LE746:  sta $00                         ;Store result.
LE748:  lda $01                         ;
LE74A:  adc #$70                        ;Add #$7000 to result.
LE74C:  sta $01                         ;$0000 = (MapY*32)+MapX+#$7000.
LE74E:  ldy #$00                        ;
LE750:  lda ($00),y                     ;Load room number.
LE752:  cmp #$FF                        ;Is it unused?-->
LE754:  beq ++++                        ;If so, branch to exit with carry flag set.

LE756:  sta RoomNumber                  ;Store room number.

LE758:* cmp $95D0,y                     ;Is it a special room?-->
LE75B:  beq +                           ;If so, branch to set flag to play item room music.
LE75D:  iny                             ;
LE75E:  cpy #$07                        ;
LE760:  bne -                           ;Loop until all special room numbers are checked.

LE762:  lda ItemRoomMusicStatus         ;Load item room music status.
LE764:  beq ++                          ;Branch if not in special room.
LE766:  lda #$80                        ;Ptop playing item room music after next music start.
LE768:  bne ++                          ;Branch always.

LE76A:* lda #$01                        ;Start item room music on next music start.
LE76C:* sta ItemRoomMusicStatus         ;
LE76E:  clc                             ;Clear carry flag. was able to get room number.
LE76F:* rts                             ;

;-----------------------------------------------------------------------------------------------------

LE770:  ldx PageIndex
        lda EnRadY,x
        clc
        adc #$08
        jmp LE783

LE77B:  ldx PageIndex
        lda #$00
        sec
        sbc EnRadY,x
LE783:  sta $02
        lda #$08
        sta $04
        jsr LE792
        lda EnRadX,x
        jmp LE7BD

LE792:  lda EnXRoomPos,x
        sta $09     ; X coord
        lda EnYRoomPos,x
        sta $08     ; Y coord
        lda EnNameTable,x
        sta $0B     ; hi coord
        rts

CheckMoveUp:
LE7A2:  ldx PageIndex
        lda ObjRadY,x
        clc
        adc #$08
        jmp +

CheckMoveDown:
        ldx PageIndex
        lda #$00
        sec
        sbc ObjRadY,x
*       sta $02
        jsr LE8BE
        lda ObjRadX,x
LE7BD:  bne +
        sec
        rts

*       sta $03
        tay
        ldx #$00
        lda $09
        sec
        sbc $03
        and #$07
        beq +
        inx
*       jsr LE8CE
        sta $04
        jsr LE90F
        ldx #$00
        ldy #$08
        lda $00
LE7DE:  bne +++
        stx $06
        sty $07
        ldx $04

; object<-->background crash detection

LE7E6:  jsr MakeCartRAMPtr              ;($E96A)Find object position in room RAM.
        ldy #$00
        lda ($04),y     ; get tile value
        cmp #$4E
        beq LE81E
        jsr $95C0
        jsr LD651
        bcc Exit16      ; CF = 0 if tile # < $80 (solid tile)... CRASH!!!
        cmp #$A0        ; is tile >= A0h? (walkable tile)
        bcs IsWalkableTile
        jmp IsBlastTile  ; tile is $80-$9F (blastable tiles)

IsWalkableTile:
        ldy IsSamus
        beq ++
    ; special case for Samus
        dey          ; = 0
        sty SamusDoorData
        cmp #$A0        ; crash with tile #$A0? (scroll toggling door)
        beq +
        cmp #$A1        ; crash with tile #$A1? (horizontal scrolling door)
        bne ++
        inc SamusDoorData
*       inc SamusDoorData
*       dex
        beq +
        jsr LE98E
        jmp LE7E6

*       sec          ; no crash
        Exit16:
        rts

LE81E:  ldx UpdatingProjectile
        beq ClcExit
        ldx #$06
*       lda $05
        eor $5D,x
        and #$04
        bne +++
        lda $04
        eor $5C,x
        and #$1F
        bne +++
        txa
        jsr Amul8       ; * 8
        ora #$80
        tay
        lda ObjAction,y
        beq +++
        lda $0307,y
        lsr
        bcs ++
        ldx PageIndex
        lda ObjAction,x
        eor #$0B
        beq +
        lda ObjAction,x
        eor #$04
        bne PlaySnd4
        lda AnimResetIndex,x
        eor #$91
        bne PlaySnd4
*       lda $0683
        ora #$02
        sta $0683
*       lda #$04
        sta $030A,y
        bne ClcExit
*       dex
        dex
        bpl ----
        lda $04
        jsr Adiv8       ; / 8
        and #$01
        tax
        inc $0366,x

ClcExit:
        clc
        rts

PlaySnd4:
        jmp SFX_Metal

CheckMoveLeft:
        ldx PageIndex
        lda ObjRadX,x
        clc
        adc #$08
        jmp +

CheckMoveRight:
        ldx PageIndex
        lda #$00
        sec
        sbc ObjRadX,x
*       sta $03
        jsr LE8BE
        ldy ObjRadY,x
LE89B:  bne +
        sec
        rts

*       sty $02
        ldx #$00
        lda $08
        sec
        sbc $02
        and #$07
        beq +
        inx
*       jsr LE8CE
        sta $04
        jsr LE90F
        ldx #$08
        ldy #$00
        lda $01
        jmp LE7DE

LE8BE:  lda ObjectHi,x
        sta $0B
        lda ObjectY,x
        sta $08
        lda ObjectX,x
        sta $09
        rts

LE8CE:  eor #$FF
        clc
        adc #$01
        and #$07
        sta $04
        tya
        asl
        sec
        sbc $04
        bcs +
        adc #$08
*       tay
        lsr
        lsr
        lsr
        sta $04
        tya
        and #$07
        beq +
        inx
*       txa
        clc
        adc $04
        rts

LE8F1:  ldx PageIndex
        lda EnRadX,x
        clc
        adc #$08
        jmp LE904

LE8FC:  ldx PageIndex
        lda #$00
        sec
        sbc EnRadX,x
LE904:  sta $03
        jsr LE792
        ldy EnRadY,x
        jmp LE89B

LE90F:  lda $02
        bpl ++
        jsr LE95F
        bcs +
        cpx #$F0
        bcc +++
*       txa
        adc #$0F
        jmp LE934

*       jsr LE95F
        lda $08
        sec
        sbc $02
        tax
        and #$07
        sta $00
        bcs +
        txa
        sbc #$0F
LE934:  tax
        lda ScrollDir
        and #$02
        bne +
        inc $0B
*       stx $02
        ldx #$00
        lda $03
        bmi +
        dex
*       lda $09
        sec
        sbc $03
        sta $03
        and #$07
        sta $01
        txa
        adc #$00
        beq +
        lda ScrollDir
        and #$02
        beq +
        inc $0B
*       rts

LE95F:  lda $08
        sec
        sbc $02
        tax
        and #$07
        sta $00
        rts

;------------------------------------[ Object pointer into cart RAM ]-------------------------------

;Find object's equivalent position in room RAM based on object's coordinates.
;In: $02 = ObjectY, $03 = ObjectX, $0B = ObjectHi. Out: $04 = cart RAM pointer.

MakeCartRAMPtr:
LE96A:  lda #$18                        ;Set pointer to $6xxx(cart RAM).
LE96C:  sta $05                         ;
LE96E:  lda $02                         ;Object Y room position.
LE970:  and #$F8                        ;Drop 3 LSBs. Only use multiples of 8.
LE972:  asl                             ;
LE973:  rol $05                         ;
LE975:  asl                             ;Move upper 2 bits to lower 2 bits of $05 and move y bits-->
LE976:  rol $05                         ;3, 4, 5 to upper 3 bits of $04.
LR978:  sta $04                         ;
LE97A:  lda $03                         ;Object X room position.
LE97C:  lsr                             ;
LE97D:  lsr                             ;
LE97E:  lsr                             ;A=ObjectX/8.
LE97F:  ora $04                         ;
LE981:  sta $04                         ;Put bits 0 thru 4 into $04.
LE983:  lda $0B                         ;Object nametable.
LE985:  asl                             ;
LE986:  asl                             ; A=ObjectHi*4.
LE987:  and #$04                        ;Set bit 2 if object is on nametable 3.
LE989:  ora $05                         ;
LE98B:  sta $05                         ;Include nametable bit in $05.
LE98D:  rts                             ;Return pointer in $04 = 01100HYY YYYXXXXX.

;---------------------------------------------------------------------------------------------------

LE98E:  lda $02
        clc
        adc $06
        sta $02
        cmp #$F0
        bcc +
        adc #$0F
        sta $02
        lda ScrollDir
        and #$02
        bne +
        inc $0B
*       lda $03
        clc
        adc $07
        sta $03
        bcc +
        lda ScrollDir
        and #$02
        beq +
        inc $0B
*       rts

LE9B7:  lda PPUCNT0ZP
        eor #$03
        sta PPUCNT0ZP
        rts

IsBlastTile:
        ldy UpdatingProjectile
        beq Exit18
LE9C2:  tay
        jsr $95BD
        cpy #$98
        bcs +++++
; attempt to find a vacant tile slot
        ldx #$C0
*       lda TileRoutine,x
        beq +                           ; 0 = free slot
        jsr Xminus16
        bne -
        lda TileRoutine,x
        bne ++++                        ; no more slots, can't blast tile
*       inc TileRoutine,x
        lda $04
        and #$DE
        sta TileWRAMLo,x
        lda $05
        sta TileWRAMHi,x
        lda InArea
        cmp #$11                        ; In Norfair?
        bne +
        cpy #$76                        ; Special case for the four-small-bubbles breakable block
        bne +
        lda #$04
        bne ++
*       tya                             ; Destroyed block ID
        clc
        adc #$10
        and #$3C
        lsr
*       lsr
        sta TileType,x
*       clc
Exit18: rts

;------------------------------------------[ Select room RAM ]---------------------------------------

SelectRoomRAM:
LEA05:  jsr GetNameTable                ;($EB85)Find name table to draw room on.
LEA08:  asl                             ;
LEA09:  asl                             ;
LEA0A:  ora #$60                        ;A=#$64 for name table 3, A=#$60 for name table 0.
LEA0C:  sta CartRAMPtr+1                ;
LEA0E:  lda #$00                        ;
LEA10:  sta CartRAMPtr                  ;Save two byte pointer to start of proper room RAM.
LEA12:  rts                             ;

;------------------------------------[ write attribute table data ]----------------------------------

AttribTableWrite:
LEA13:* lda RoomNumber                  ;
LEA15:  and #$0F                        ;Determine what row of PPU attribute table data, if any,-->
LEA17:  inc RoomNumber                  ;to load from RoomRAM into PPU.
LEA19:  jsr ChooseRoutine               ;

;The following table is used by the code above to determine when to write to the PPU attribute table.

LEA1c:  .word ExitSub                   ;($C45C)Rts.
LEA1E:  .word WritePPUAttribTbl         ;($E5E2)Write first row of PPU attrib data.
LEA20:  .word ExitSub                   ;($C45C)Rts.
LEA22:  .word WritePPUAttribTbl         ;($E5E2)Write second row of PPU attrib data.
LEA24:  .word RoomFinished              ;($EA26)Finished writing attribute table data.

;-----------------------------------[ Finished writing room data ]-----------------------------------

RoomFinished:
LEA26:  lda #$FF                        ;No more tasks to perform on current room.-->
LEA28:  sta RoomNumber                  ;Set RoomNumber to #$FF.
LEA2A:* rts                             ;

;------------------------------------------[ Setup room ]--------------------------------------------

SetupRoom:
LEA2B:  lda RoomNumber                  ;Room number.
LEA2D:  cmp #$FF                        ;
LEA2F:  beq -                           ;Branch to exit if room is undefined.
LEA31:  cmp #$FE                        ;
LEA33:  beq +                           ;Branch if empty place holder byte found in room data.
LEA35:  cmp #$F0                        ;
LEA37:  bcs --                          ;Branch if time to write PPU attribute table data.
LEA39:  jsr UpdateRoomSpriteInfo        ;($EC9B)Update which sprite belongs on which name table.

LEA3C:  jsr ScanForItems                ;($ED98)Set up any special items.
LEA3F:  lda RoomNumber                  ;Room number to load.
LEA41:  asl                             ;*2(for loading address of room pointer).
LEA42:  tay                             ;
LEA43:  lda (RoomPtrTable),y            ;Low byte of 16-bit room pointer.-->
LEA45:  sta RoomPtr                     ;Base copied from $959A to $3B.
LEA47:  iny                             ;
LEA48:  lda (RoomPtrTable),y            ;High byte of 16-bit room pointer.-->
LEA4A:  sta RoomPtr+1                   ;Base copied from $959B to $3C.
LEA4C:  ldy #$00                        ;
LEA4E:  lda (RoomPtr),y                 ;First byte of room data.
LEA50:  sta RoomPal                     ;store initial palette # to fill attrib table with.
LEA52:  lda #$01                        ;
LEA54:  jsr AddToRoomPtr                ;($EAC0)Increment room data pointer.
LEA57:  jsr SelectRoomRAM               ;($EA05)Determine where to draw room in RAM, $6000 or $6400.
LEA5A:  jsr InitTables                  ;($EFF8)clear Name Table & do initial Attrib table setup.
LEA5D:* jmp DrawRoom                    ;($EAAA)Load room contents into room RAM.

;---------------------------------------[ Draw room object ]-----------------------------------------

DrawObject:
LEA60:  sta $0E                         ;Store object position byte(%yyyyxxxx).
LEA62:  lda CartRAMPtr                  ;
LEA64:  sta CartRAMWorkPtr              ;Set the working pointer equal to the room pointer-->
LEA66:  lda CartRAMPtr+1                ;(start at beginning of the room).
LEA68:  sta CartRAMWorkPtr+1            ;
LEA6A:  lda $0E                         ;Reload object position byte.
LEA6C:  jsr Adiv16                      ;($C2BF)/16. Lower nibble contains object y position.-->
LEA6F:  tax                             ;Transfer it to X, prepare for loop.
LEA70:  beq +++                         ;Skip y position calculation loop as y position=0 and-->
                                        ;does not need to be calculated.
LEA72:* lda CartRAMWorkPtr              ;LoW byte of pointer working in room RAM.
LEA74:  clc                             ;
LEA75:  adc #$40                        ;Advance two rows in room RAM(one y unit).
LEA77:  sta CartRAMWorkPtr              ;
LEA79:  bcc +                           ;If carry occurred, increment high byte of pointer-->
LEA7B:  inc CartRAMWorkPtr+1            ;in room RAM.
LEA7D:* dex                             ;
LEA7E:  bne --                          ;Repeat until at desired y position(X=0).

LEA80:* lda $0E                         ;Reload object position byte.
LEA82:  and #$0F                        ;Remove y position upper nibble.
LEA84:  asl                             ;Each x unit is 2 tiles.
LEA85:  adc CartRAMWorkPtr              ;
LEA87:  sta CartRAMWorkPtr              ;Add x position to room RAM work pointer.
LEA89:  bcc +                           ;If carry occurred, increment high byte of room RAM work-->
LEA8B:  inc CartRAMWorkPtr+1            ;pointer, else branch to draw object.

;CartRAMWorkPtr now points to the object's starting location (upper left corner)
;on the room RAM which will eventually be loaded into a name table.

LEA8D:* iny                             ;Move to the next byte of room data which is-->
LEA8E:  lda (RoomPtr),y                 ;the index into the structure pointer table.
LEA90:  tax                             ;Transfer structure pointer index into X.
LEA91:  iny                             ;Move to the next byte of room data which is-->
LEA92:  lda (RoomPtr),y                 ;the attrib table info for the structure.
LEA94:  sta ObjectPal                   ;Save attribute table info.
LEA96:  txa                             ;Restore structure pointer to A.
LEA97:  asl                             ;*2. Structure pointers are two bytes in size.
LEA98:  tay                             ;
LEA99:  lda (StructPtrTable),y          ;Low byte of 16-bit structure ptr.
LEA9B:  sta StructPtr                   ;
LEA9D:  iny                             ;
LEA9E:  lda (StructPtrTable),y          ;High byte of 16-bit structure ptr.
LEAA0:  sta StructPtr+1                 ;
LEAA2:  jsr DrawStruct                  ;($EF8C)Draw one structure.
LEAA5:  lda #$03                        ;Move to next set of structure data.
LEAA7:  jsr AddToRoomPtr                ;($EAC0)Add A to room data pointer.

;-------------------------------------------[ Draw room ]--------------------------------------------

;The following function draws a room in the room RAM which is eventually loaded into a name table.

DrawRoom:
LEAAA:  ldy #$00                        ;Zero index.
LEAAC:  lda (RoomPtr),y                 ;Load byte of room data.-->
LEAAE:  cmp #$FF                        ;Is it #$FF(end-of-room)?-->
LEAB0:  beq EndOfRoom                   ;If so, branch to exit.
LEAB2:  cmp #$FE                        ;Place holder for empty room objects(not used).
LEAB4:  beq +                           ;
LEAB6:  cmp #$FD                        ;is A=#$FD(end-of-objects)?-->
LEAB8:  bne DrawObject                  ;If not, branch to draw room object.-->
LEABA:  beq EndOfObjs                   ;Else branch to set up enemies/doors.
LEABC:* sta RoomNumber                  ;Store #$FE if room object is empty.
LEABE:  lda #$01                        ;Prepare to increment RoomPtr.

;-------------------------------------[ Add A to room pointer ]--------------------------------------

AddToRoomPtr:
LEAC0:  clc                             ;Prepare to add index in A to room pointer.
LEAC1:  adc RoomPtr                     ;
LEAC3:  sta RoomPtr                     ;
LEAC5:  bcc +                           ;Did carry occur? If not branch to exit.
LEAC7:  inc RoomPtr+1                   ;Increment high byte of room pointer if carry occured.
LEAC9:* rts                             ;

;----------------------------------------------------------------------------------------------------

EndOfObjs:
LEACA:  lda RoomPtr                     ;
LEACC:  sta $00                         ;Store room pointer in $0000.
LEACE:  lda RoomPtr+1                   ;
LEAD0:  sta $01                         ;
LEAD2:  lda #$01                        ;Prepare to increment to enemy/door data.

EnemyLoop:
LEAD4:  jsr AddToPtr00                  ;($EF09)Add A to pointer at $0000.
LEAD7:  ldy #$00                        ;
LEAD9:  lda ($00),y                     ;Get first byte of enemy/door data.
LEADB:  cmp #$FF                        ;End of enemy/door data?-->
LEADD:  beq EndOfRoom                   ;If so, branch to finish room setup.
LEADF:  and #$0F                        ;Discard upper four bits of data.
LEAE1:  jsr ChooseRoutine               ;Jump to proper enemy/door handling routine.

;Pointer table to code.

LEAE4:  .word ExitSub                   ;($C45C)Rts.
LEAE6:  .word LoadEnemy                 ;($EB06)Room enemies.
LEAE8:  .word LoadDoor                  ;($EB8C)Room doors.
LEAEA:  .word ExitSub                   ;($C45C)Rts.
LEAEC:  .word LoadElevator              ;($EC04)Elevator.
LEAEE:  .word ExitSub                   ;($C45C)Rts.
LEAF0:  .word LoadStatues               ;($EC2F)Kraid & Ridley statues.
LEAF2:  .word ZebHole                   ;($EC57)Regenerating enemies(such as Zeb).

EndOfRoom:
LEAF4:  ldx #$F0                        ;Prepare for PPU attribute table write.
        stx RoomNumber                  ;
        lda ScrollDir                   ;
        sta TempScrollDir               ;Make temp copy of ScrollDir.
        and #$02                        ;Check if scrolling left or right.
        bne +                           ;
        jmp LE57C
*       jmp LE70C

LoadEnemy:
LEB06:  jsr GetEnemyData                ;($EB0C)Get enemy data from room data.
LEB09:  jmp EnemyLoop                   ;($EAD4)Do next room object.

GetEnemyData:
LEB0C:  lda ($00),y                     ;Get 1st byte again.
        and #$F0                        ;Get object slot that enemy will occupy.
        tax                             ;
        jsr IsSlotTaken                 ;($EB7A)Check if object slot is already in use.
        bne ++                          ;Exit if object slot taken.
        iny                             ;
        lda ($00),y                     ;Get enemy type.
        jsr GetEnemyType                ;($EB28)Load data about enemy.
        ldy #$02                        ;
        lda ($00),y                     ;Get enemy initial position(%yyyyxxxx).
        jsr LEB4D
        pha
*       pla
*       lda #$03                        ;Number of bytes to add to ptr to find next room item.
        rts                             ;

GetEnemyType:
LEB28:  pha                             ;Store enemy type.
        and #$C0                        ;If MSB is set, the "tough" version of the enemy  
        sta EnSpecialAttribs,x          ;is to be loaded(more hit points, except rippers).
        asl                             ;
        bpl ++                          ;If bit 6 is set, the enemy is either Kraid or Ridley.
        lda InArea                      ;Load current area Samus is in(to check if Kraid or-->
        and #$06                        ;Ridley is alive or dead).
        lsr                             ;Use InArea to find status of Kraid/Ridley statue.
        tay                             ;
        lda MaxMissiles,y               ;Load status of Kraid/Ridley statue.
        beq +                           ;Branch if Kraid or Ridley needs to be loaded.
        pla                             ;
        pla                             ;Mini boss is dead so pull enemy info and last address off-->
        jmp --                          ;stack so next enemy/door item can be loaded.

*       lda #$01                        ;Samus is in Kraid or Ridley's room and the-->
        sta KraidRidleyPresent          ;mini boss is alive and needs to be loaded.

*       pla                             ;Restore enemy type data.
        and #$3F                        ;Keep 6 lower bits to use as index for enemy data tables.
        sta EnDataIndex,x               ;Store index byte.
        rts                             ;

LEB4D:  tay                             ;Save enemy position data in Y.
        and #$F0                        ;Extract Enemy y position.
        ora #$08                        ;Add 8 pixels to y position so enemy is always on screen. 
        sta EnYRoomPos,x                ;Store enemy y position.
        tya                             ;Restore enemy position data.
        jsr Amul16                      ;*16 to extract enemy x position.
        ora #$0C                        ;Add 12 pixels to x position so enemy is always on screen.
        sta EnXRoomPos,x                ;Store enemy x position.
        lda #$01                        ;
        sta EnStatus,x                  ;Indicate object slot is taken.
        lda #$00
        sta $0404,x
        jsr GetNameTable                ;($EB85)Get name table to place enemy on.
        sta EnNameTable,x               ;Store name table.
        ldy EnDataIndex,x               ;Load A with index to enemy data.
        asl $0405,x                     ;*2
        jsr LFB7B
        jmp LF85A

IsSlotTaken:
LEB7A:  lda EnStatus,x
        beq +
        lda $0405,x
        and #$02
*       rts

;------------------------------------------[ Get name table ]----------------------------------------

;The following routine is small but is called by several other routines so it is important and
;requires some explaining to understand its function.  First of all, as Samus moves from one room
;to the next, she is also moving from one name table to the next.  Samus does not move from one
;name table to the next as one might think. Samus moves diagonally through the name tables. To
;understand this concept, one must first know how the name tables are arranged.  They are arranged
;like so:
;
; +-----+-----+                                                  +-----+-----+
; |     |     | The following is an incorrect example of how     |     |     |
; |  2  |  3  | Samus goes from one name table to the next-----> |  2  |  3  |
; |     |     |                                                  |     |     |
; +-----+-----+                                                  +-----+-----+
; |     |     |                                                  |     |     |
; |  0  |  1  |                               INCORRECT!------>  |  0<-|->1  |
; |     |     |                                                  |     |     |
; +-----+-----+                                                  +-----+-----+
;
;The following are examples of how the name tables are properly traversed while walking through rooms:
;
;          +-----+-----+                                     +-----+-----+
;          |     |     |                                     |     |     |
;          |  2  | ->3 |                                     |  2  |  3<-|-+
;          |     |/    |                                     |     |     | |
;          +-----+-----+     <--------CORRECT!-------->      +-----+-----+ |
;          |    /|     |                                     |     |     | |
;          | 0<- |  1  |                                   +-|->0  |  1  | |
;          |     |     |                                   | |     |     | |
;          +-----+-----+                                   | +-----+-----+ |
;                                                          +---------------+
;
;The same diagonal traversal of the name tables illustrated above applies to vetricle traversal as
;well. Since Samus can only travel between 2 name tables and not 4, the name table placement for
;objects is simplified.  The following code determines which name table to use next:

GetNameTable:
LEB85:  lda PPUCNT0ZP                   ;
LEB87:  eor ScrollDir                   ;Store #$01 if object should be loaded onto name table 3-->
LEB89:  and #$01                        ;store #$00 if it should be loaded onto name table 0.
LEB8B:  rts                             ;

;----------------------------------------------------------------------------------------------------

; LoadDoor
; ========

        LoadDoor:
        jsr LEB92
*       jmp EnemyLoop    ; do next room object

LEB92:  iny
        lda ($00),y     ; door info byte
        pha
        jsr Amul16      ; CF = door side (0=right, 1=left)
        php
        lda MapPosX
        clc
        adc MapPosY
        plp
        rol
        and #$03
        tay
        ldx $EC00,y
        pla          ; retrieve door info
        and #$03
        sta $0307,x     ; door palette
        tya
        pha
        lda $0307,x
        cmp #$01
        beq ++
        cmp #$03
        beq ++
        lda #$0A
        sta $09
        ldy MapPosX
        txa
        jsr Amul16       ; * 16
        bcc +
        dey
*       tya
        jsr LEE41
        jsr LEE4A
        bcs ++
*       lda #$01
        sta ObjAction,x
*       pla
        and #$01        ; A = door side (0=right, 1=left)
        tay
        jsr GetNameTable                ;($EB85)
        sta ObjectHi,x
        lda DoorXs,y    ; get door's X coordinate
        sta ObjectX,x
        lda #$68        ; door Y coord is always #$68
        sta ObjectY,x
        lda LEBFE,y
        tay
        jsr GetNameTable                ;($EB85)
        eor #$01
        tax
        tya
        ora DoorOnNameTable3,x
        sta DoorOnNameTable3,x
        lda #$02
        rts

DoorXs:
        .byte $F0        ; X coord of RIGHT door
        .byte $10        ; X coord of LEFT door
LEBFE:  .byte $02
        .byte $01
LEC00:  .byte $80
        .byte $B0
        .byte $A0
        .byte $90

; LoadElevator
; ============

        LoadElevator:
        jsr LEC09
        bne ----           ; branch always

LEC09:  lda ElevatorStatus
        bne +      ; exit if elevator already present
        iny
        lda ($00),y
        sta $032F
        ldy #$83
        sty $032D       ; elevator Y coord
        lda #$80
        sta $032E       ; elevator X coord
        jsr GetNameTable                ;($EB85)
        sta $032C       ; high Y coord
        lda #$23
        sta $0323       ; elevator frame
        inc ElevatorStatus              ;1
*       lda #$02
        rts

; LoadStatues
; ===========

        LoadStatues:
        jsr GetNameTable                ;($EB85)
        sta $036C
        lda #$40
        ldx RidleyStatueStatus
        bpl +      ; branch if Ridley statue not hit
        lda #$30
*       sta $0370
        lda #$60
        ldx KraidStatueStatus
        bpl +      ; branch if Kraid statue not hit
        lda #$50
*       sta $036F
        sty $54
        lda #$01
        sta $0360
*       jmp EnemyLoop   ; do next room object

ZebHole:
LEC57:  ldx #$20
*       txa
        sec
        sbc #$08
        bmi +
        tax
        ldy $0728,x
        iny
        bne -
        ldy #$00
        lda ($00),y
        and #$F0
        sta $0729,x
        iny
        lda ($00),y
        sta $0728,x
        iny
        lda ($00),y
        tay
        and #$F0
        ora #$08
        sta $072A,x
        tya
        jsr Amul16       ; * 16
        ora #$00
        sta $072B,x
        jsr GetNameTable                ;($EB85)
        sta $072C,x
*       lda #$03
        bne ---

OnNameTable0:
LEC93:  lda PPUCNT0ZP                   ;
        eor #$01                        ;If currently on name table 0,-->
        and #$01                        ;return #$01. Else return #$00.
        tay                             ;
        rts                             ;

UpdateRoomSpriteInfo:
LEC9B:  ldx ScrollDir
        dex
        ldy #$00
        jsr UpdateDoorData              ;($ED51)Update name table 0 door data.
        iny
        jsr UpdateDoorData              ;($ED51)Update name table 3 door data.
        ldx #$50
        jsr GetNameTable                ;($EB85)
        tay
*       tya
        eor EnNameTable,x
        lsr
        bcs +
        lda $0405,x
        and #$02
        bne +
        sta EnStatus,x
*       jsr Xminus16
        bpl --
        ldx #$18
*       tya
        eor $B3,x
        lsr
        bcs +
        lda #$00
        sta $B0,x
*       txa
        sec
        sbc #$08
        tax
        bpl --
        jsr LED65
        jsr LED5B
        jsr GetNameTable                ;(EB85)
        asl
        asl
        tay
        ldx #$C0
*       tya
        eor TileWRAMHi,x
        and #$04
        bne +
        sta $0500,x
*       jsr Xminus16
        cmp #$F0
        bne --
        tya
        lsr
        lsr
        tay
        ldx #$D0
        jsr LED7A
        ldx #$E0
        jsr LED7A
        ldx #$F0
        jsr LED7A
        tya
        sec
        sbc $032C
        bne +
        sta ElevatorStatus
*       ldx #$1E
*       lda $0704,x
        bne +
        lda #$FF
        sta $0700,x
*       txa
        sec
        sbc #$06
        tax
        bpl --
        cpy $036C
        bne +
        lda #$00
        sta $0360
*       ldx #$18
*       tya
        cmp $072C,x
        bne +
        lda #$FF
        sta $0728,x
*       txa
        sec
        sbc #$08
        tax
        bpl --
        ldx #$00
        jsr LED8C
        ldx #$08
        jsr LED8C
        jmp $95AE

UpdateDoorData:
LED51:  txa                             ;
LED52:  eor #$03                        ;
LED54:  and $006C,y                     ;Moves door info from one name table to the next-->
LED57:* sta $006C,y                     ;when the room is transferred across name tables.
LED5A:  rts                             ;

LED5B:  jsr GetNameTable                ;($EB85)
        eor #$01
        tay
        lda #$00
        beq -
LED65:  ldx #$B0
*       lda ObjAction,x
        beq +
        lda ObjectOnScreen,x
        bne +
        sta ObjAction,x
*       jsr Xminus16
        bmi --
        rts

LED7A:  lda ObjAction,x
        cmp #$05
        bcc +
        tya
        eor ObjectHi,x
        lsr
        bcs +
        sta ObjAction,x
*       rts

LED8C:  tya
        cmp PowerUpNameTable,x
        bne Exit11
        lda #$FF
        sta PowerUpType,x
Exit11: rts

;---------------------------------------[ Setup special items ]--------------------------------------

;The following routines look for special items on the game map and jump to
;the appropriate routine to handle those items.

ScanForItems:
LED98:  lda SpecItmsTable               ;Low byte of ptr to 1st item data.
LED9B:  sta $00                         ;
LED9D:  lda SpecItmsTable+1             ;High byte of ptr to 1st item data.

ScanOneItem:
LEDA0:  sta $01                         ;
LEDA2:  ldy #$00                        ;Index starts at #$00.
LEDA4:  lda ($00),y                     ;Load map Ypos of item.-->
LEDA6:  cmp MapPosY                     ;Does it equal Samus' Ypos on map?-->
LEDA8:  beq +                           ;If yes, check Xpos too.

LEDAA:  bcs Exit11                      ;Exit if item Y pos >  Samus Y Pos.
LEDAC:  iny                             ;
LEDAD:  lda ($00),y                     ;Low byte of ptr to next item data.
LEDAF:  tax                             ;
LEDB0:  iny                             ;
LEDB1:  and ($00),y                     ;AND with hi byte of item ptr.
LEDB3:  cmp #$FF                        ;if result is FFh, then this was the last item-->
LEDB5:  beq Exit11                      ;(item ptr = FFFF). Branch to exit.

LEDB7:  lda ($00),y                     ;High byte of ptr to next item data.
LEDB9:  stx $00                         ;Write low byte for next item.
LEDBB:  jmp ScanOneItem                 ;Process next item.

LEDBE:* lda #$03                        ;Get ready to look at byte containing X pos.
LEDC0:  jsr AddToPtr00                  ;($EF09)Add 3 to pointer at $0000.

ScanItemX:
LEDC3:  ldy #$00                        ;
LEDC5:  lda ($00),y                     ;Load map Xpos of object.-->
LEDC7:  cmp MapPosX                     ;Does it equal Samus' Xpos on map?-->
LEDC9:  beq +                           ;If so, then load object.
LEDCB:  bcs Exit11                      ;Exit if item pos X > Samus Pos X.

LEDCD:  iny                             ;
LEDCE:  jsr AnotherItem                 ;($EF00)Check for another item on same Y pos.
LEDD1:  jmp ScanItemX                   ;Try next X coord.

LEDD4:* lda #$02                        ;Move ahead two bytes to find item data.

ChooseHandlerRoutine:
LEDD6:  jsr AddToPtr00                  ;($EF09)Add A to pointer at $0000.
LEDD9:  ldy #$00                        ;
LEDDB:  lda ($00),y                     ;Object type
LEDDD:  and #$0F                        ;Object handling routine index stored in 4 LSBs.
LEDDF:  jsr ChooseRoutine               ;($C27C)Load proper handling routine from table below.

;Handler routines jumped to by above code.

LEDE2:  .word ExitSub                   ;($C45C)rts.
LEDE4:  .word SqueeptHandler            ;($EDF8)Some squeepts.
LEDE6:  .word PowerUpHandler            ;($EDFE)power-ups.
LEDE8:  .word SpecEnemyHandler          ;($EE63)Special enemies(Mellows, Melias and Memus).
LEDEA:  .word ElevatorHandler           ;($EEA1)Elevators.
LEDEC:  .word CannonHandler             ;($EEA6)Mother brain room cannons.
LEDEE:  .word MotherBrainHandler        ;($EEAE)Mother brain.
LEDF0:  .word ZeebetiteHandler          ;($EECA)Zeebetites.
LEDF2:  .word RinkaHandler              ;($EEEE)Rinkas.
LEDF4:  .word DoorHandler               ;($EEF4)Some doors.
LEDF6:  .word PaletteHandler            ;($EEFA)Background palette change.

;---------------------------------------[ Squeept handler ]------------------------------------------

SqueeptHandler:
LEDF8:  jsr GetEnemyData                ;($EB0C)Load Squeept data.
LEDFB:* jmp ChooseHandlerRoutine        ;($EDD6)Exit handler routines.

;--------------------------------------[ Power-up Handler ]------------------------------------------

PowerUpHandler:
LEDFE:  iny                             ;Prepare to store item type.
LEDFF:  ldx #$00                        ;
LEE01:  lda #$FF                        ;
LEE03:  cmp PowerUpType                 ;Is first power-up item slot available?-->
LEE06:  beq +                           ;if yes, branch to load item.

LEE08:  ldx #$08                        ;Prepare to check second power-up item slot.
LEE0A:  cmp PowerUpBType                ;Is second power-up item slot available?-->                     
LEE0D:  bne ++                          ;If not, branch to exit.
LEE0F:* lda ($00),y                     ;Power-up item type.
LEE11:  jsr PrepareItemID               ;($EE3D)Get unique item ID.
LEE14:  jsr CheckForItem                ;($EE4A)Check if Samus already has item.
LEE17:  bcs +                           ;Samus already has item. do not load it.

LEE19:  ldy #$02                        ;Prepare to load item coordinates.
LEE1B:  lda $09                         ;
LEE1D:  sta PowerUpType,x               ;Store power-up type in available item slot.
LEE20:  lda ($00),y                     ;Load x and y screen positions of item.
LEE22:  tay                             ;Save position data for later processing.
LEE23:  and #$F0                        ;Extract Y coordinate.
LEE25:  ora #$08                        ;+ 8 to find  Y coordinate center.
LEE27:  sta PowerUpYCoord,x             ;Store center Y coord
LEE2A:  tya                             ;Reload position data.
LEE2B:  jsr Amul16                      ;($C2C5)*16. Move lower 4 bits to upper 4 bits.
LEE2E:  ora #$08                        ;+ 8 to find X coordinate center.
LEE30:  sta PowerUpXCoord,x             ;Store center X coord
LEE33:  jsr GetNameTable                ;($EB85)Get name table to place item on.
LEE36:  sta PowerUpNameTable,x          ;Store name table Item is located on.

LEE39:* lda #$03                        ;Get next data byte(Always #$00).
LEE3B:  bne ---                         ;Branch always to exit handler routines.
        
PrepareItemID:
LEE3D:  sta $09                         ;Store item type.
LEE3E:  lda MapPosX                     ;

LEE41:  sta $07                         ;Store item X coordinate.
LEE42:  lda MapPosY                     ;
LEE45:  sta $06                         ;Store item Y coordinate.
LEE47:  jmp CreateItemID                ;($DC67)Get unique item ID.

CheckForItem:
LEE4A:  ldy NumberOfUniqueItems         ;
LEE4D:  beq +++                         ;Samus has no unique items. Load item and exit.
LEE4F:* lda $07                         ;
LEE51:  cmp NumberOfUniqueItems,y       ;Look for lower byte of unique item.
LEE54:  bne +                           ;
LEE56:  lda $06                         ;Look for upper byte of unique item.
LEE58:  cmp DataSlot,y                  ;
LEE5B:  beq +++                         ;Samus already has item. Branch to exit.
LEE5D:* dey                             ;
LEE5E:  dey                             ;
LEE5F:  bne --                          ;Loop until all Samus' unique items are checked.
LEE61:* clc                             ;Samus does not have the item. It will be placed on screen.
LEE62:* rts                             ;

;-----------------------------------------------------------------------------------------------------

SpecEnemyHandler:
LEE63:  ldx #$18
        lda RandomNumber1
        adc FrameCount
        sta $8A
*       jsr LEE86
        txa
        sec
        sbc #$08
        tax
        bpl -
        lda $95E4
        sta $6BE9
        sta $6BEA
        lda #$01
        sta $6BE4
*       jmp ChooseHandlerRoutine        ;($EDD6)Exit handler routines.

LEE86:  lda $B0,x
        bne +
        txa
        adc $8A
        and #$7F
        sta $B1,x
        adc RandomNumber2
        sta $B2,x
        jsr GetNameTable                ;($EB85)
        sta $B3,x
        lda #$01
        sta $B0,x
        rol $8A
*       rts

ElevatorHandler:
LEEA1:  jsr LEC09
        bne --                          ;Branch always.

CannonHandler:
LEEA6:  jsr $95B1
        lda #$02
*       jmp ChooseHandlerRoutine        ;($EDD6)Exit handler routines.

MotherBrainHandler:
LEEAE:  jsr $95B4
        lda #$38
        sta $07
        lda #$00
        sta $06
        jsr LEE4A
        bcc LEEC6
        lda #$08
        sta MotherBrainStatus
        lda #$00
        sta MotherBrainHits
LEEC6:  lda #$01
        bne -

ZeebetiteHandler:
LEECA:  jsr $95B7
        txa
        lsr
        adc #$3C
        sta $07
        lda #$00
        sta $06
        jsr LEE4A
        bcc +
        lda #$81
        sta $0758,x
        lda #$01
        sta $075D,x
        lda #$07
        sta $075B,x
*       jmp LEEC6

RinkaHandler:
LEEEE:  jsr $95BA
        jmp LEEC6

DoorHandler:
LEEF4:  jsr LEB92
        jmp ChooseHandlerRoutine        ;($EDD6)Exit handler routines.

PaletteHandler:
LEEFA:  lda ScrollDir
        sta $91
        bne LEEC6

AnotherItem:
LEF00:  lda ($00),y                     ;Is there another item with same Y pos?-->
        cmp #$FF                        ;If so, A is amount to add to ptr. to find X pos.
        bne AddToPtr00                  ;($EF09)
        pla                             ;
        pla                             ;No more items to check. Pull last subroutine-->
        rts                             ;off stack and exit.

AddToPtr00:
LEF09:  clc                             ;
        adc $00                         ;
        sta $00                         ;A is added to the 16 bit address stored in $0000.
        bcc +                           ;
        inc $01                         ;
*       rts                             ;

;----------------------------------[ Draw structure routines ]----------------------------------------

;Draws one row of the structure.
;A = number of 2x2 tile macros to draw horizontally.

DrawStructRow:
LEF13:  and #$0F                        ;Row length(in macros). Range #$00 thru #$0F.
LEF15:  bne +                           ;
LEF17:  lda #$10                        ;#$00 in row length=16.
LEF19:* sta $0E                         ;Store horizontal macro count.
LEF1B:  lda (StructPtr),y               ;Get length byte again.
LEF1D:  jsr Adiv16                      ;($C2BF)/16. Upper nibble contains x coord offset(if any).
LEF20:  asl                             ;*2, because a macro is 2 tiles wide.
LEF21:  adc CartRAMWorkPtr              ;Add x coord offset to CartRAMWorkPtr and save in $00.
LEF23:  sta $00                         ;
LEF25:  lda #$00                        ;
LEF27:  adc CartRAMWorkPtr+1            ;Save high byte of work pointer in $01.
LEF29:  sta $01                         ;$0000 = work pointer.

DrawMacro:
LEF2B:  lda $01                         ;High byte of current location in room RAM.
LEF2D:  cmp #$63                        ;Check high byte of room RAM address for both room RAMs-->
LEF2F:  beq +                           ;to see if the attribute table data for the room RAM has-->
LEF31:  cmp #$67                        ;been reached.  If so, branch to check lower byte as well.
LEF33:  bcc ++                          ;If not at end of room RAM, branch to draw macro.
LEF35:  beq +                           ;
LEF37:  rts                             ;Return if have gone past room RAM(should never happen).

LEF38:* lda $00                         ;Low byte of current nametable address.
LEF3A:  cmp #$A0                        ;Reached attrib table?-->
LEF3C:  bcc +                           ;If not, branch to draw the macro.
LEF3E:  rts                             ;Can't draw any more of the structure, exit.

LEF3F:* inc $10                         ;Increase struct data index.
LEF41:  ldy $10                         ;Load struct data index into Y.
LEF43:  lda (StructPtr),y               ;Get macro number.
LEF45:  asl                             ;
LEF46:  asl                             ;A=macro number * 4. Each macro is 4 bytes long.
LEF47:  sta $11                         ;Store macro index.
LEF49:  ldx #$03                        ;Prepare to copy four tile numbers.
LEF4B:* ldy $11                         ;Macro index loaded into Y.
LEF4D:  lda (MacroPtr),y                ;Get tile number.
LEF4F:  inc $11                         ;Increase macro index
LEF51:  ldy TilePosTable,x              ;get tile position in macro.
LEF54:  sta ($00),y                     ;Write tile number to room RAM.
LEF56:  dex                             ;Done four tiles yet?-->
LEF57:  bpl -                           ;If not, loop to do another.
LEF59:  jsr UpdateAttrib                ;($EF9E)Update attribute table if necessary
LEF5C:  ldy #$02                        ;Macro width(in tiles).
LEF5E:  jsr AddYToPtr00                 ;($C2A8)Add 2 to pointer to move to next macro.
LEF61:  lda $00                         ;Low byte of current room RAM work pointer.
LEF63:  and #$1F                        ;Still room left in current row?-->
LEF65:  bne +                           ;If yes, branch to do another macro.

;End structure row early to prevent it from wrapping on to the next row..
LEF67:  lda $10                         ;Struct index.
LEF69:  clc                             ;
LEF6A:  adc $0E                         ;Add number of macros remaining in current row.
LEF6C:  sec                             ;
LEF6D:  sbc #$01                        ;-1 from macros remaining in current row.
LEF6F:  jmp AdvanceRow                  ;($EF78)Move to next row of structure.

LEF72:* dec $0E                         ;Have all macros been drawn on this row?-->
LEF74:  bne DrawMacro                   ;If not, branch to draw another macro.
LEF76:  lda $10                         ;Load struct index.

AdvanceRow:
LEF78:  sec                             ;Since carry bit is set,-->
LEF79:  adc StructPtr                   ;addition will be one more than expected.
LEF7B:  sta StructPtr                   ;Update the struct pointer.
LEF7D:  bcc +                           ;
LEF7F:  inc StructPtr+1                 ;Update high byte of struct pointer if carry occured.
LEF81:* lda #$40                        ;
LEF83:  clc                             ;
LEF84:  adc CartRAMWorkPtr              ;Advance to next macro row in room RAM(two tile rows).
LEF86:  sta CartRAMWorkPtr              ;
LEF88:  bcc DrawStruct                  ;Begin drawing next structure row.
LEF8A:  inc CartRAMWorkPtr+1            ;Increment high byte of pointer if necessary.

DrawStruct:
LEF8C:  ldy #$00                        ;Reset struct index.
LEF8E:  sty $10                         ;
LEF90:  lda (StructPtr),y               ;Load data byte.
LEF92:  cmp #$FF                        ;End-of-struct?-->
LEF94:  beq +                           ;If so, branch to exit.
LEF96:  jmp DrawStructRow               ;($EF13)Draw a row of macros.
LEF99:* rts                             ;

;The following table is used to draw macros in room RAM. Each macro is 2 x 2 tiles.
;The following table contains the offsets required to place the tiles in each macro.

TilePosTable:
LEF9A:  .byte $21                       ;Lower right tile.
LEF9B:  .byte $20                       ;Lower left tile.
LEF9C:  .byte $01                       ;Upper right tile.
LEF9D:  .byte $00                       ;Upper left tile.

;---------------------------------[ Update attribute table bits ]------------------------------------

;The following routine updates attribute bits for one 2x2 tile section on the screen.

UpdateAttrib:
LEF9E:  lda ObjectPal                   ;Load attribute data of structure.
LEFA0:  cmp RoomPal                     ;Is it the same as the room's default attribute data?-->
LEFA2:  beq +++++                       ;If so, no need to modify the attribute table, exit.

;Figure out cart RAM address of the byte containing the relevant bits.

LEFA4:  lda $00                         ;
LEFA6:  sta $02                         ;
LEFA8:  lda $01                         ;
LEFAA:  lsr                             ;
LEFAB:  ror $02                         ;
LEFAD:  lsr                             ;
LEFAE:  ror $02                         ;
LEFB0:  lda $02                         ;The following section of code calculates the-->
LEFB2:  and #$07                        ;proper attribute byte that corresponds to the-->
LEFB4:  sta $03                         ;macro that has just been placed in the room RAM.
LEFB6:  lda $02                         ;
LEFB8:  lsr                             ;
LEFB9:  lsr                             ;
LEFBA:  and #$38                        ;
LEFBC:  ora $03                         ;
LEFBE:  ora #$C0                        ;
LEFC0:  sta $02                         ;
LEFC2:  lda #$63                        ;
LEFC4:  sta $03                         ;$0002 contains pointer to attribute byte.

LEFC6:  ldx #$00                        ;
LEFC8:  bit $00                         ;
LEFCA:  bvc +                           ;
LEFCC:  ldx #$02                        ;The following section of code figures out which-->
LEFCE:* lda $00                         ;pair of bits to modify in the attribute table byte-->
LEFD0:  and #$02                        ;for the macro that has just been placed in the-->
LEFD2:  beq +                           ;room RAM.
LEFD4:  inx                             ;

;X now contains which macro attribute table bits to modify:
;+---+---+
;| 0 | 1 |
;+---+---+
;| 2 | 3 |
;+---+---+
;Where each box represents a macro(2x2 tiles).

;The following code clears the old attribute table bits and sets the new ones.
LEFD5:* lda $01                         ;Load high byte of work pointer in room RAM.
LEFD7:  and #$04                        ;
LEFD9:  ora $03                         ;Choose proper attribute table associated with the-->
LEFDB:  sta $03                         ;current room RAM.
LEFDD:  lda AttribMaskTable,x           ;Choose appropriate attribute table bit mask from table below.
LEFE0:  ldy #$00                        ;
LEFE2:  and ($02),y                     ;clear the old attribute table bits.
LEFE4:  sta ($02),y                     ;
LEFE6:  lda ObjectPal                   ;Load new attribute table data(#$00 thru #$03).
LEFE8:* dex                             ;
LEFE9:  bmi +                           ;
LEFEB:  asl                             ;
LEFEC:  asl                             ;Attribute table bits shifted one step left
LEFED:  bcc -                           ;Loop until attribute table bits are in the proper location.
LEFEF:* ora ($02),y                     ;
LEFF1:  sta ($02),y                     ;Set attribute table bits.
LEFF3:* rts                             ;

AttribMaskTable:
LEFF4:  .byte %11111100                 ;Upper left macro.
LEFF5:  .byte %11110011                 ;Upper right macro.
LEFF6:  .byte %11001111                 ;Lower left macro.
LEFF7:  .byte %00111111                 ;Lower right macro.

;------------------------[ Initialize room RAM and associated attribute table ]-----------------------

InitTables:
LEFF8:  lda CartRAMPtr+1                ;#$60 or #$64.
LEFFA:  tay                             ;
LEFFB:  tax                             ;Save value to create counter later.
LEFFC:  iny                             ;
LEFFD:  iny                             ;High byte of address to fill to ($63 or $67).
LEFFE:  iny                             ;
LEFFF:  lda #$FF                        ;Value to fill room RAM with.
LF001:  jsr FillRoomRAM                 ;($F01C)Fill entire RAM for designated room with #$FF.

LF004:  ldx $01                         ;#$5F or #$63 depening on which room RAM was initialized.
LF006:  jsr Xplus4                      ;($E193)X = X + 4.
LF009:  stx $01                         ;Set high byte for attribute table write(#$63 or #$67).
LF00B:  ldx RoomPal                     ;Index into table below (Lowest 2 bits).
LF00D:  lda ATDataTable,x               ;Load attribute table data from table below.
LF010:  ldy #$C0                        ;Low byte of start of all attribute tables.
LF012:* sta ($00),y                     ;Fill attribute table.
LF014:  iny                             ;
LF015:  bne -                           ;Loop until entire attribute table is filled.
LF017:  rts                             ;

ATDataTable:       
LF018:  .byte %00000000                 ;
LF019:  .byte %01010101                 ;Data to fill attribute tables with.
LF01A:  .byte %10101010                 ;
LF01B:  .byte %11111111                 ;

FillRoomRAM:
LF01C:  pha                             ;Temporarily store A.
LF01D:  txa                             ;
LF01E:  sty $01                         ;Calculate value to store in X to use as upper byte-->
LF020:  clc                             ;counter for initilaizing room RAM(X=#$FC).-->
LF021:  sbc $01                         ;Since carry bit is cleared, result is one less than expected.
LF023:  tax                             ;
LF024:  pla                             ;Restore value to fill room RAM with(#$FF).
LF025:  ldy #$00                        ;Lower address byte to start at.
LF027:  sty $00                         ;
LF029:* sta ($00),y                     ;
LF02B:  dey                             ;
LF02C:  bne -                           ;
LF02E:  dec $01                         ;Loop until all the room RAM is filled with #$FF(black).
LF030:  inx                             ;
LF031:  bne -                           ;
LF033:  rts                             ;

;----------------------------------------------------------------------------------------------------

; Crash detection
; ===============

LF034:  lda #$FF
        sta $73
        sta $010F
; check for crash with Memus
        ldx #$18
*      lda $B0,x
        beq +++++           ; branch if no Memu in slot
        cmp #$03
        beq +++++
        jsr LF19A
        jsr IsSamusDead
        beq +
        lda SamusBlink
        bne +
        ldy #$00
        jsr LF149
        jsr LF2B4
    ; check for crash with bullets
*       ldy #$D0
*       lda ObjAction,y       ; projectile active?
        beq ++            ; try next one if not
        cmp #wa_BulletExplode
        bcc +
        cmp #$07
        beq +
        cmp #wa_BombExplode
        beq +
        cmp #wa_Missile
        bne ++
*       jsr LF149
        jsr LF32A
*      jsr Yplus16
        bne ---
*       txa
        sec
        sbc #$08                ; each Memu occupies 8 bytes
        tax
        bpl ------

        ldx #$B0
*       lda ObjAction,x
        cmp #$02
        bne +
        ldy #$00
        jsr IsSamusDead
        beq ++
        jsr AreObjectsTouching          ;($DC7F)
        jsr LF277
*       jsr Xminus16
        bmi --
; enemy <--> bullet/missile/bomb detection
*       ldx #$50                ; start with enemy slot #5
LF09F:  lda EnStatus,x       ; slot active?
        beq +              ; branch if not
        cmp #$03
*       beq NextEnemy      ; next slot
        jsr LF152
        lda EnStatus,x
        cmp #$05
        beq ++++
        ldy #$D0                ; first projectile slot
*       lda ObjAction,y  ; is it active?
        beq ++            ; branch if not
        cmp #wa_BulletExplode
        bcc +
        cmp #$07
        beq +
        cmp #wa_BombExplode
        beq +
        cmp #wa_Missile
        bne ++
; check if enemy is actually hit
*       jsr LF140
        jsr LF2CA
*       jsr Yplus16          ; next projectile slot
        bne ---
*       ldy #$00
        lda SamusBlink
        bne NextEnemy
        jsr IsSamusDead
        beq NextEnemy
        jsr LF140
        jsr LF282
        NextEnemy:
        jsr Xminus16
        bmi +
        jmp LF09F

*       ldx #$00
        jsr LF172
        ldy #$60
*       lda EnStatus,y
        beq +
        cmp #$05
        beq +
        lda SamusBlink
        bne +
        jsr IsSamusDead
        beq +
        jsr LF1B3
        jsr LF162
        jsr LF1FA
        jsr LF2ED
*       jsr Yplus16
        cmp #$C0
        bne --
        ldy #$00
        jsr IsSamusDead
        beq ++++
        jsr LF186
        ldx #$F0
*       lda ObjAction,x
        cmp #$07
        beq +
        cmp #$0A
        bne ++
*       jsr LDC82
        jsr LF311
*       jsr Xminus16
        cmp #$C0
        bne ---                 
*       jmp SubtractHealth              ;($CE92)

LF140:  jsr LF1BF
        jsr LF186
        jmp LF1FA

LF149:  jsr LF186
        jsr LF1D2
        jmp LF1FA

LF152:  lda EnYRoomPos,x
        sta $07  ; Y coord
        lda EnXRoomPos,x
        sta $09  ; X coord
        lda EnNameTable,x     ; hi coord
        jmp LF17F

LF162:  lda EnYRoomPos,y     ; Y coord
        sta $06
        lda EnXRoomPos,y     ; X coord
        sta $08
        lda EnNameTable,y     ; hi coord
        jmp LF193

GetObject0CoordData:
LF172:  lda ObjectY,x
        sta $07
        lda ObjectX,x
        sta $09
        lda ObjectHi,x

LF17F:  eor PPUCNT0ZP
        and #$01
        sta $0B
        rts

GetObject1CoordData:
LF186:  lda ObjectY,y
        sta $06
        lda ObjectX,y
        sta $08
        lda ObjectHi,y

LF193:  eor PPUCNT0ZP
        and #$01
        sta $0A
        rts

LF19A:  lda $B1,x
        sta $07
        lda $B2,x
        sta $09
        lda $B3,x
        jmp LF17F

DistFromObj0ToObj1:
LF1A7:  lda ObjRadY,x
        jsr LF1E0
        lda ObjRadX,x
        jmp LF1D9

DistFromObj0ToEn1:
LF1B3:  lda ObjRadY,x
        jsr LF1E7
        lda ObjRadX,x
        jmp LF1CB

DistFromEn0ToObj1:
LF1BF:  lda EnRadY,x
        jsr LF1E0
        lda EnRadX,x
        jmp LF1D9

AddEnemy1XRadius:
LF1CB:  clc
        adc EnRadX,y
        sta $05
        rts

LF1D2:  lda #$04
        jsr LF1E0
        lda #$08

AddObject1XRadius:
LF1D9:  clc
        adc ObjRadX,y
        sta $05
        rts

AddObject1YRadius:
LF1E0:  clc
        adc ObjRadY,y
        sta $04
        rts

LF1E7:  clc
        adc EnRadY,y
        sta $04
        rts

; Y = Y + 16

Yplus16:
        tya
        clc
        adc #$10
        tay
        rts

; X = X - 16

Xminus16:
        txa
        sec
        sbc #$10
        tax
        rts

LF1FA:  lda #$02
        sta $10
        and ScrollDir
        sta $03
        lda $07                         ;Load object 0 y coord.
        sec                             ;
        sbc $06                         ;Subtract object 1 y coord.
        sta $00                         ;Store difference in $00.
        lda $03
        bne ++
        lda $0B
        eor $0A
        beq ++
        jsr LF262
        lda $00
        sec
        sbc #$10
        sta $00
        bcs +
        dec $01
*       jmp LF22B

*       lda #$00
        sbc #$00
        jsr LF266

LF22B:  sec
        lda $01
        bne ++
        lda $00
        sta $11
        cmp $04
        bcs ++
        asl $10
        lda $09
        sec
        sbc $08
        sta $00
        lda $03
        beq +
        lda $0B
        eor $0A
        beq +
        jsr LF262
        jmp LF256

*       sbc #$00
        jsr LF266
LF256:  sec
        lda $01
        bne +
        lda $00
        sta $0F
        cmp $05
*       rts

LF262:  lda $0B
        sbc $0A

LF266:  sta $01
        bpl +
        jsr LE449
        inc $10
*       rts

LF270:  ora $030A,x
        sta $030A,x
        rts

LF277:  bcs Exit17
LF279:  lda $10
LF27B:  ora $030A,y
        sta $030A,y
        Exit17:
        rts

LF282:  bcs Exit17
        jsr LF2E8
        jsr IsScrewAttackActive         ;($CD9C)Check if screw attack active.
        ldy #$00
        bcc +++
        lda EnStatus,x
        cmp #$04
        bcs Exit17
        lda EnDataIndex,x
*       sta $010F
        tay
        bmi +
        lda $968B,y
        and #$10
        bne Exit17
*       ldy #$00
        jsr LF338
        jmp LF306

*       lda #$81
        sta $040E,x
        bne ++
LF2B4:  bcs +
        jsr IsScrewAttackActive         ;($CD9C)Check if screw attack active.
        ldy #$00
        lda #$C0
        bcs ---
LF2BF:  lda $B6,x
        and #$F8
        ora $10
        eor #$03
        sta $B6,x
*       rts

LF2CA:  bcs +++
        lda ObjAction,y
        sta $040E,x
        jsr LF279
*       jsr LF332
*       ora $0404,x
        sta $0404,x
*       rts

LF2DF:  lda $10
        ora $0404,y
        sta $0404,y
        rts

LF2E8:  jsr LF340
        bne --
LF2ED:  bcs +
        jsr LF2DF
        tya
        pha
        jsr IsScrewAttackActive         ;($CD9C)Check if screw attack active.
        pla
        tay
        bcc +
        lda #$80
        sta $010F
        jsr LF332
        jsr LF270
LF306:  lda $95CE
        sta HealthLoChange
        lda $95CF
        sta HealthHiChange
*       rts

LF311:  bcs Exit22
        lda #$E0
        sta $010F
        jsr LF338
        lda $0F
        beq +
        lda #$01
*       sta $73

ClearHealthChange:
LF323:  lda #$00
LF325:  sta HealthLoChange
LF327:  sta HealthHiChange

Exit22: 
LF329:  rts                             ;Return for routine above and below.

LF32A:  bcs Exit22
        jsr LF279
        jmp LF2BF

LF332:  jsr LF340
        jmp Amul8       ; * 8

LF338:  lda $10
        asl
        asl
        asl
        jmp LF27B

LF340:  lda $10
        eor #$03
        rts

; UpdateEnemies
; =============

UpdateEnemies:
LF345:  ldx #$50                ;Load x with #$50
*       jsr DoOneEnemy                  ;($F351)
        ldx PageIndex
        jsr Xminus16
        bne -
DoOneEnemy:
LF351:  stx PageIndex                   ;PageIndex starts at $50 and is subtracted by #$0F each-->
                                        ;iteration. There is a max of 6 enemies at a time.
        ldy EnStatus,x
        beq +
        cpy #$03
        bcs +
        jsr LF37F
*       jsr LF3AA
        lda EnStatus,x
        sta $81
        cmp #$07
        bcs +
        jsr ChooseRoutine

; Pointer table to code

        .word ExitSub       ;($C45C) rts
        .word $F3BE
        .word $F3E6
        .word $F40D
        .word $F43E
        .word $F483
        .word $F4EE

*       jmp KillObject                  ;($FA18)Free enemy data slot.

LF37F:  lda $0405,x
        and #$02
        bne +
        lda EnYRoomPos,x     ; Y coord
        sta $0A
        lda EnXRoomPos,x     ; X coord
        sta $0B
        lda EnNameTable,x     ; hi coord
        sta $06
        lda EnRadY,x
        sta $08
        lda EnRadX,x
        sta $09
        jsr IsObjectVisible             ;($DFDF)Determine if object is within the screen boundaries.
        txa
        bne +
        pla
        pla
*       ldx PageIndex
        rts

LF3AA:  lda $0405,x
        asl
        rol
        tay
        txa
        jsr Adiv16                      ;($C2BF)/16.
        eor FrameCount
        lsr
        tya
        ror
        ror
        sta $0405,x
        rts

LF3BE:  lda $0405,x
        asl
        bmi +
        lda #$00
        sta $6B01,x
        sta EnCounter,x
        sta $040A,x
        jsr LF6B9
        jsr LF75B
        jsr LF682
        jsr LF676
        lda EnDelay,x
        beq +
        jsr LF7BA
*       jmp ++

LF3E6:  lda $0405,x
        asl
        bmi ++
        lda $0405,x
        and #$20
        beq +
        ldy EnDataIndex,x
        lda EnemyInitDelayTbl,y         ;($96BB)
        sta EnDelay,x
        dec EnStatus,x
        bne ++
*       jsr LF6B9
        jsr LF75B
        jsr LF51E
LF40A:* jsr LF536
        jmp $95E5

LF410:  jsr UpdateEnemyAnim
        jsr $8058
LF416:  ldx PageIndex
        lda EnSpecialAttribs,x
        bpl +
        lda ObjectCntrl
        bmi +
        lda #$A3
LF423:  sta ObjectCntrl
*       lda EnStatus,x
        beq LF42D
        jsr LDD8B
LF42D:  ldx PageIndex
        lda #$00
        sta $0404,x
        sta $040E,x
        rts

LF438:  jsr UpdateEnemyAnim
LF43B:  jmp LF416

LF43E:  jsr LF536
        lda EnStatus,x
        cmp #$03
        beq LF410
        bit ObjectCntrl
        bmi +
        lda #$A1
        sta ObjectCntrl
*       lda FrameCount
        and #$07
        bne +
        dec $040D,x
        bne +
        lda EnStatus,x
        cmp #$03
        beq +
        lda $040C,x
        sta EnStatus,x
        ldy EnDataIndex,x
        lda $969B,y
        sta $040D,x
*       lda $040D,x
        cmp #$0B
        bcs +
        lda FrameCount
        and #$02
        beq +
        asl ObjectCntrl
*       jmp LF416

LF483:  lda $0404,x
        and #$24
        beq ++++++
        jsr KillObject                  ;($FA18)Free enemy data slot.
        ldy EnAnimFrame,x
        cpy #$80
        beq PickupMissile
        tya
        pha
        lda EnDataIndex,x
        pha
        ldy #$00
        ldx #$03
        pla
        bne ++
        dex
        pla
        cmp #$81
        bne +
        ldx #$00                        ;Increase HealthHi by 0.
        ldy #$50                        ;Increase HealthLo by 5.
*       pha
*       pla                             
        sty HealthLoChange
        stx HealthHiChange
        jsr AddHealth                   ;($CEF9)Add health to Samus.
        jmp SFX_EnergyPickup

PickupMissile:
        lda #$02
        ldy EnDataIndex,x
        beq +
        lda #$1E
*       clc
        adc MissileCount
        bcs +              ; can't have more than 255 missiles
        cmp MaxMissiles  ; can Samus hold this many missiles?
        bcc ++            ; branch if yes
*       lda MaxMissiles  ; set to max. # of missiles allowed
*       sta MissileCount
        jmp SFX_MissilePickup

*       lda FrameCount
        and #$03
        bne +
        dec $040D,x
        bne +
        jsr KillObject                  ;($FA18)Free enemy data slot.
*       lda FrameCount
        and #$02
        lsr
        ora #$A0
        sta ObjectCntrl
        jmp LF416

LF4EE:  dec EnSpecialAttribs,x
        bne ++
        lda $040C,x
        tay
        and #$C0
        sta EnSpecialAttribs,x
        tya
        and #$3F
        sta EnStatus,x
        pha
        jsr $80B0
        and #$20
        beq +
        pla
        jsr LF515
        pha
*       pla
*       lda #$A0
        jmp LF423

LF515:  sta $040C,x
LF518:  lda #$04
        sta EnStatus,x
        rts

LF51E:  lda ScrollDir
        ldx PageIndex
        cmp #$02
        bcc ++
        lda EnYRoomPos,x     ; Y coord
        cmp #$EC
        bcc ++
        jmp KillObject                  ;($FA18)Free enemy data slot.

*       jsr SFX_MetroidHit
        jmp GetPageIndex

LF536:  lda EnSpecialAttribs,x
        sta $0A
        lda $0404,x
        and #$20
        beq +
        lda $040E,x
        cmp #$03
        bne +++
        bit $0A
        bvs +++
        lda EnStatus,x
        cmp #$04
        beq +++
        jsr LF515
        lda #$40
        sta $040D,x
        jsr $80B0
        and #$20
        beq +
        lda #$05
        sta EnHitPoints,x
        jmp $95A8
*       rts

*       jsr $80B0
        and #$20
        bne ---
        jsr SFX_Metal
        jmp LF42D

*       lda EnHitPoints,x
        cmp #$FF
        beq --
        bit $0A
        bvc +
        jsr SFX_BossHit
        bne ++
*       jsr LF74B
        and #$0C
        beq PlaySnd1
        cmp #$04
        beq PlaySnd2
        cmp #$08
        beq PlaySnd3
        jsr SFX_MetroidHit
        bne +       ; branch always
PlaySnd1:
        jsr SFX_EnemyHit
        bne +       ; branch always
PlaySnd2:
        jsr SFX_EnemyHit
        bne +       ; branch always
PlaySnd3:
        jsr SFX_BigEnemyHit             ;($CBCE)
*       ldx PageIndex
        jsr $80B0
        and #$20
        beq +
        lda $040E,x
        cmp #$0B
        bne ----
*       lda EnStatus,x
        cmp #$04
        bne +
        lda $040C,x
*       ora $0A
        sta $040C,x
        asl
        bmi +
        jsr $80B0
        and #$20
        bne +
        ldy $040E,x
        cpy #$0B
        beq +++++
        cpy #$81
        beq +++++
*       lda #$06
        sta EnStatus,x
        lda #$0A
        bit $0A
        bvc +
        lda #$03
*       sta EnSpecialAttribs,x
        cpy #$02
        beq +
        bit $0A
        bvc ++
        ldy $040E,x
        cpy #$0B
        bne ++
        dec EnHitPoints,x
        beq +++
        dec EnHitPoints,x
        beq +++
*       dec EnHitPoints,x
        beq ++
*       dec EnHitPoints,x
        bne GetPageIndex
*       lda #$03
        sta EnStatus,x
        bit $0A
        bvs +
        lda $040E,x
        cmp #$02
        bcs +
        lda #$00
        jsr LDCFC
        ldx PageIndex
*       jsr LF844
        lda $960B,y
        jsr LF68D
        sta EnCounter,x
        ldx #$C0
*       lda EnStatus,x
        beq +
        txa
        clc
        adc #$08
        tax
        cmp #$E0
        bne -
        beq GetPageIndex
*       lda $95DD
        jsr LF68D
        lda #$0A
        sta EnCounter,x
        inc EnStatus,x
        lda #$00
        bit $0A
        bvc +
        lda #$03
*       sta $0407,x
        ldy PageIndex
        lda EnYRoomPos,y
        sta EnYRoomPos,x
        lda EnXRoomPos,y
        sta EnXRoomPos,x
        lda EnNameTable,y
        sta EnNameTable,x
        GetPageIndex:
        ldx PageIndex
        rts

LF676:  jsr $80B0
        asl
        asl
        asl
        and #$C0
        sta $6B03,x
        rts

LF682:  jsr LF844
        lda $963B,y
        cmp EnResetAnimIndex,x
        beq +
LF68D:  sta EnResetAnimIndex,x
LF690:  sta EnAnimIndex,x
LF693:  lda #$00
        sta EnAnimDelay,x
*       rts

LF699:  jsr LF844
        lda $965B,y
        cmp EnResetAnimIndex,x
        beq Exit12
        jsr LF68D
        ldy EnDataIndex,x
        lda $967B,y
        and #$7F
        beq Exit12
        tay
*       dec EnAnimIndex,x
        dey
        bne -
Exit12: rts

LF6B9:  lda #$00
        sta $82
        jsr LF74B
        tay
        lda EnStatus,x
        cmp #$02
        bne +
        tya
        and #$02
        beq Exit12
*       tya
        dec $040D,x
        bne Exit12
        pha
        ldy EnDataIndex,x
        lda $969B,y
        sta $040D,x
        pla
        bpl ++++
        lda #$FE
        jsr LF7B3
        lda ScrollDir
        cmp #$02
        bcc +
        jsr LF752
        bcc +
        tya
        eor PPUCNT0ZP
        bcs +++
*       lda EnXRoomPos,x
        cmp ObjectX
        bne +
        inc $82
*       rol
*       and #$01
        jsr LF744
        lsr
        ror
        eor $0403,x
        bpl +
        jsr $81DA
*       lda #$FB
        jsr LF7B3
        lda ScrollDir
        cmp #$02
        bcs +
        jsr LF752
        bcc +
        tya
        eor PPUCNT0ZP
        bcs +++
*       lda EnYRoomPos,x
        cmp ObjectY
        bne +
        inc $82
        inc $82
*       rol
*       and #$01
        asl
        asl
        jsr LF744
        lsr
        lsr
        lsr
        ror
        eor $0402,x
        bpl +
        jmp $820F

LF744:  ora $0405,x
        sta $0405,x
*       rts

LF74B:  ldy EnDataIndex,x
        lda $968B,y
        rts

LF752:  lda EnNameTable,x
        tay
        eor ObjectHi
        lsr
        rts

LF75B:  lda #$E7
        sta $06
        lda #$18
        jsr LF744
        ldy EnDataIndex,x
        lda $96AB,y
        beq +++++
        tay
        lda $0405,x
        and #$02
        beq ++++
        tya
        ldy #$F7
        asl
        bcs +
        ldy #$EF
*       lsr
        sta $02
        sty $06
        lda ObjectY
        sta $00
        ldy EnYRoomPos,x
        lda $0405,x
        bmi +
        ldy ObjectX
        sty $00
        ldy EnXRoomPos,x
*       lda ObjectHi
        lsr
        ror $00
        lda EnNameTable,x
        lsr
        tya
        ror
        sec
        sbc $00
        bpl +
        jsr TwosCompliment              ;($C3D4)
*       lsr
        lsr
        lsr
        cmp $02
        bcc ++
*       lda $06
LF7B3:  and $0405,x
        sta $0405,x
*       rts

LF7BA:  dec EnDelay,x
        bne +
        lda $0405,x
        and #$08
        bne ++
        inc EnDelay,x
*       rts

*       lda EnDataIndex,x
        cmp #$07
        bne +
        jsr SFX_OutOfHole
        ldx PageIndex
*       inc EnStatus,x
        jsr LF699
        ldy EnDataIndex,x
        lda $96CB,y
        clc
        adc #$D1
        sta $00
        lda #$00
        adc #$97
        sta $01
        lda FrameCount
        eor RandomNumber1
        ldy #$00
        and ($00),y
        tay
        iny
        lda ($00),y
        sta $0408,x
        jsr $80B0
        bpl ++
        lda #$00
        sta EnCounter,x
        sta $0407,x
        ldy $0408,x
        lda $972B,y
        sta $6AFE,x
        lda $973F,y
        sta $6AFF,x
        lda $9753,y
        sta $0402,x
        lda $9767,y
        sta $0403,x
        lda $0405,x
        bmi +
        lsr
        bcc ++
        jsr $81D1
        jmp ++

*       and #$04
        beq +
        jsr $8206
*       lda #$DF
        jmp LF7B3

LF83E:  lda $0405,x
LF841:  jmp +

LF844:  lda $0405,x
        bpl +
        lsr
        lsr
*       lsr
        lda EnDataIndex,x
        rol
        tay
        rts

LF852:  txa
        lsr
        lsr
        lsr
        adc FrameCount
        lsr
        rts

LF85A:  ldy EnDataIndex,x
        lda $969B,y
        sta $040D,x
        lda EnemyHitPointTbl,y          ;($962B)
        ldy EnSpecialAttribs,x
        bpl +
        asl
*       sta EnHitPoints,x
*       rts

LF870:  lda $0405,x
        and #$10
        beq -
        lda $87
        and EnStatus,x
        beq -
        lda $87
        bpl +
        ldy $6B01,x
        bne -
*       jsr LF8E8
        bcs ++
        sta $0404,y
        jsr LF92C
        lda $0405,x
        lsr
        lda $85
        pha
        rol
        tax
        lda $978B,x
        pha
        tya
        tax
        pla
        jsr LF68D
        ldx PageIndex
        lda #$01
        sta EnStatus,y
        and $0405,x
        tax
        lda Table15,x
        sta $0403,y
        lda #$00
        sta $0402,y
        ldx PageIndex
        jsr LF8F8
        lda $0405,x
        lsr
        pla
        tax
        lda $97A3,x
        sta $04
        txa
        rol
        tax
        lda $979B,x
        sta $05
        jsr LF91D
        ldx PageIndex
        bit $87
        bvc ++
        lda $0405,x
        and #$01
        tay
        lda $0083,y
        jmp LF690

LF8E8:  ldy #$60
        clc
*       lda EnStatus,y
        beq +
        jsr Yplus16
        cmp #$C0
        bne -
*       rts

LF8F8:  lda $85
        cmp #$02
        bcc +
        ldx PageIndex
        lda $0405,x
        lsr
        lda $88
        rol
        and #$07
        sta $040A,y
        lda #$02
        sta EnStatus,y
        lda #$00
        sta EnDelay,y
        sta EnAnimDelay,y
        sta $0408,y
*       rts

LF91D:  ldx PageIndex
        jsr LE792
        tya
        tax
        jsr LFD8F
        jmp LFA49

; Table used by above subroutine

Table15:
        .byte $02
        .byte $FE

LF92C:  lda #$02
        sta EnRadY,y
        sta EnRadX,y
        ora $0405,y
        sta $0405,y
        rts

LF93B:  ldx #$B0
*       jsr LF949
        ldx PageIndex
        jsr Xminus16
        cmp #$60
        bne -
LF949:  stx PageIndex
        lda $0405,x
        and #$02
        bne +
        jsr KillObject                  ;($FA18)Free enemy data slot.
*       lda EnStatus,x
        beq Exit19
        jsr ChooseRoutine

; Pointer table to code

        .word ExitSub     ;($C45C) rts
        .word $F96A
        .word LF991       ; spit dragon's fireball
        .word ExitSub     ;($C45C) rts
        .word $FA6B
        .word $FA91

Exit19: rts

LF96A:  jsr LFA5B
        jsr LFA1E
        ldx PageIndex
        bcs LF97C
        lda EnStatus,x
        beq Exit19
        jsr LFA60
LF97C:  lda #$01
LF97E:  jsr UpdateEnemyAnim
        jmp LDD8B

*       inc $0408,x
LF987:  inc $0408,x
        lda #$00
        sta EnDelay,x
        beq +
LF991:  jsr LFA5B
        lda $040A,x
        and #$FE
        tay
        lda $97A7,y
        sta $0A
        lda $97A8,y
        sta $0B
*       ldy $0408,x
        lda ($0A),y
        cmp #$FF
        bne +
        sta $0408,x
        jmp LF987

*       cmp EnDelay,x
        beq ---
        inc EnDelay,x
        iny
        lda ($0A),y
        jsr $8296
        ldx PageIndex
        sta $0402,x
        lda ($0A),y
        jsr $832F
        ldx PageIndex
        sta $0403,x
        tay
        lda $040A,x
        lsr
        php
        bcc +
        tya
        jsr TwosCompliment              ;($C3D4)
        sta $0403,x
*       plp
        bne +
        lda $0402,x
        beq +
        bmi +
        ldy $040A,x
        lda $95E0,y
        sta EnResetAnimIndex,x
*       jsr LFA1E
        ldx PageIndex
        bcs ++
        lda EnStatus,x
        beq Exit20
        ldy #$00
        lda $040A,x
        lsr
        beq +
        iny
*       lda $95E2,y
        jsr LF68D
        jsr LF518
        lda #$0A
        sta EnDelay,x
*       jmp LF97C

KillObject:
LFA18:  lda #$00                        ;
LFA1A:  sta EnStatus,x                  ;Store #$00 as enemy status(enemy slot is open).
LFA1D:  rts                             ;

; enemy<-->background crash detection

LFA1E:  lda InArea
        cmp #$11
        bne +
        lda EnStatus,x
        lsr
        bcc ++
*       jsr LFA7D
        ldy #$00
        lda ($04),y
        cmp #$A0
        bcc ++
        ldx PageIndex
*       lda $0403,x
        sta $05
        lda $0402,x
        sta $04
LFA41:  jsr LE792
        jsr LFD8F
        bcc KillObject                  ;($FA18)Free enemy data slot.
LFA49:  lda $08
        sta EnYRoomPos,x
        lda $09
        sta EnXRoomPos,x
        lda $0B
        and #$01
        sta EnNameTable,x
*       rts

LFA5B:  lda $0404,x
        beq Exit20
LFA60:  lda #$00
        sta $0404,x
        lda #$05
        sta EnStatus,x
Exit20: rts

LFA6B:  lda EnAnimFrame,x
        cmp #$F7
        beq +
        dec EnDelay,x
        bne ++
*       jsr KillObject                  ;($FA18)Free enemy data slot.
*       jmp LF97C

LFA7D:  ldx PageIndex
        lda EnYRoomPos,x
        sta $02
        lda EnXRoomPos,x
        sta $03
        lda EnNameTable,x
        sta $0B
        jmp MakeCartRAMPtr              ;($E96A)Find enemy position in room RAM.

LFA91:  jsr KillObject                  ;($FA18)Free enemy data slot.
        lda $95DC
        jsr LF68D
        jmp LF97C

LFA9D:  ldx #$C0
*       stx PageIndex
        lda EnStatus,x
        beq +
        jsr LFAB4
*       lda PageIndex
        clc
        adc #$08
        tax
        cmp #$E0
        bne --
*      rts

LFAB4:  dec EnCounter,x
        bne ++
        lda #$0C
        sta EnCounter,x
        dec $0407,x
        bmi +
        bne ++
*       jsr KillObject                  ;($FA18)Free enemy data slot.
*       lda EnCounter,x
        cmp #$09
        bne +
        lda $0407,x
        asl
        tay
        lda Table16,y
        sta $04
        lda Table16+1,y
        sta $05
        jsr LFA41
*       lda #$80
        sta ObjectCntrl
        lda #$03
        jmp LF97E

; Table used by above subroutine

Table16:
        .byte $00
        .byte $00
        .byte $0C
        .byte $1C
        .byte $10
        .byte $F0
        .byte $F0
        .byte $08

LFAF2:  ldy #$18
*       jsr LFAFF
        lda PageIndex
        sec
        sbc #$08
        tay
        bne -

LFAFF:  sty PageIndex
        ldx $0728,y
        inx
        beq -----
        ldx $0729,y
        lda EnStatus,x
        beq +
        lda $0405,x
        and #$02
        bne Exit13
*       sta $0404,x
        lda #$FF
        cmp EnDataIndex,x
        bne +
        dec EnDelay,x
        bne Exit13
        lda $0728,y
        jsr LEB28
        ldy PageIndex
        lda $072A,y
        sta EnYRoomPos,x
        lda $072B,y
        sta EnXRoomPos,x
        lda $072C,y
        sta EnNameTable,x
        lda #$18
        sta EnRadX,x
        lda #$0C
        sta EnRadY,x
        ldy #$00
        jsr LF186
        jsr LF152
        jsr LF1BF
        jsr LF1FA
        bcc Exit13
        lda #$01
        sta EnDelay,x
        sta EnStatus,x
        and ScrollDir
        asl
        sta $0405,x
        ldy EnDataIndex,x
        jsr LFB7B
        jmp LF85A

*       sta EnDataIndex,x
        lda #$01
        sta EnDelay,x
        jmp KillObject                  ;($FA18)Free enemy data slot.

LFB7B:  jsr $80B0
        ror $0405,x
        lda EnemyInitDelayTbl,y         ;($96BB)Load initial delay for enemy movement.
        sta EnDelay,x           ;

Exit13: 
        rts                             ;Exit from multiple routines.

LFB88:  ldx PageIndex
        jsr LF844
        lda $6B01,x
        inc $6B03,x
        dec $6B03,x
        bne +
        pha
        pla
*       bpl +
        jsr TwosCompliment              ;($C3D4)
*       cmp #$08
        bcc +
        cmp #$10
        bcs Exit13
        tya
        and #$01
        tay
        lda $0085,y
        cmp EnResetAnimIndex,x
        beq Exit13
        sta EnAnimIndex,x
        dec EnAnimIndex,x
        sta EnResetAnimIndex,x
        jmp LF693

*       lda $963B,y
        cmp EnResetAnimIndex,x
        beq Exit13
        jmp LF68D

LFBCA:  ldx PageIndex
        jsr LF844
        lda $965B,y
        cmp EnResetAnimIndex,x
        beq Exit13
        sta EnResetAnimIndex,x
        jmp LF690

LFBDD:  lda #$40
        sta PageIndex
        ldx #$0C
*       jsr LFBEC
        dex
        dex
        dex
        dex
        bne -
LFBEC:  lda $A0,x
        beq ++
        dec $A0,x
        txa
        lsr
        tay
        lda Table17,y
        sta $04
        lda Table17+1,y
        sta $05
        lda $A1,x
        sta $08
        lda $A2,x
        sta $09
        lda $A3,x
        sta $0B
        jsr LFD8F
        bcc +++
        lda $08
        sta $A1,x
        sta $034D
        lda $09
        sta $A2,x
        sta $034E
        lda $0B
        and #$01
        sta $A3,x
        sta $034C
        lda $A3,x
        sta $034C
        lda #$5A
        sta PowerUpAnimFrame            ;Save index to find object animation.
        txa
        pha
        jsr DrawFrame
        lda SamusBlink
        bne +
        ldy #$00
        ldx #$40
        jsr AreObjectsTouching          ;($DC7F)
        bcs +
        jsr IsScrewAttackActive         ;($CD9C)Check if screw attack active.
        ldy #$00
        bcc +
        clc
        jsr LF311
        lda #$50
        sta HealthLoChange
        jsr SubtractHealth              ;($CE92)
*       pla
        tax
*       rts

*       lda #$00
        sta $A0,x
        rts

; Table used by above subroutine

Table17:
        .byte $00
        .byte $FB
        .byte $FB
        .byte $FE
        .byte $FB
        .byte $02
        .byte $00
        .byte $05

LFC65:  lda $6BE4
        beq ++
        ldx #$F0
        stx PageIndex
        lda $6BE9
        cmp $95E4
        bne +++
        lda #$03
        jsr UpdateEnemyAnim
        lda RandomNumber1
        sta $8A
        lda #$18
*       pha
        tax
        jsr LFC98
        pla
        tax
        lda $B6,x
        and #$F8
        sta $B6,x
        txa
        sec
        sbc #$08
        bpl -
*       rts

*      jmp KillObject                   ;($FA18)Free enemy data slot.

LFC98:  lda $B0,x
        jsr ChooseRoutine

; Pointer table to code

        .word ExitSub       ;($C45C) rts
        .word $FCA5
        .word $FCB1
        .word $FCBA

LFCA5:  jsr LFD84
        jsr LFD08
        jsr LFD25
        jmp LDD8B

LFCB1:  jsr LFD84
        jsr LFCC1
        jmp LDD8B

LFCBA:  lda #$00
        sta $B0,x
        jmp SFX_EnemyHit

LFCC1:  jsr LFD5F
        lda $B4,x
        cmp #$02
        bcs +
        ldy $08
        cpy ObjectY
        bcc +
        ora #$02
        sta $B4,x
*       ldy #$01
        lda $B4,x
        lsr
        bcc +
        ldy #$FF
*       sty $05
        ldy #$04
        lsr
        lda $B5,x
        bcc +
        ldy #$FD
*       sty $04
        inc $B5,x
        jsr LFD8F
        bcs +
        lda $B4,x
        ora #$02
        sta $B4,x
*       bcc +
        jsr LFD6C
*       lda $B5,x
        cmp #$50
        bcc +
        lda #$01
        sta $B0,x
*       rts

LFD08:  lda #$00
        sta $B5,x
        tay
        lda ObjectX
        sec
        sbc $B2,x
        bpl +
        iny
        jsr TwosCompliment              ;($C3D4)
*       cmp #$10
        bcs +
        tya
        sta $B4,x
        lda #$02
        sta $B0,x
*       rts

LFD25:  txa
        lsr
        lsr
        lsr
        adc $8A
        sta $8A
        lsr $8A
        and #$03
        tay
        lda Table18,y
        sta $04
        lda Table18+1,y
        sta $05
        jsr LFD5F
        lda $08
        sec
        sbc ScrollY
        tay
        lda #$02
        cpy #$20
        bcc +
        jsr TwosCompliment              ;($C3D4)
        cpy #$80
        bcc ++
*       sta $04
*      jsr LFD8F
        jmp LFD6C

; Table used by above subroutine

Table18:
        .byte $02
        .byte $FE
        .byte $01
        .byte $FF
        .byte $02

LFD5F:  lda $B3,x
        sta $0B
        lda $B1,x
        sta $08
        lda $B2,x
        sta $09
        rts

LFD6C:  lda $08
        sta $B1,x
        sta $04F0
        lda $09
        sta $B2,x
        sta $04F1
        lda $0B
        and #$01
        sta $B3,x
        sta $6BEB
        rts

LFD84:  lda $B6,x
        and #$04
        beq +
        lda #$03
        sta $B0,x
*       rts

LFD8F:  lda ScrollDir
        and #$02
        sta $02
        lda $04
        clc
        bmi +++
        beq LFDBF
        adc $08
        bcs +
        cmp #$F0
        bcc ++
*       adc #$0F
        ldy $02
        bne ClcExit2
        inc $0B
*       sta $08
        jmp LFDBF

*       adc $08
        bcs +
        sbc #$0F
        ldy $02
        bne ClcExit2
        inc $0B
*       sta $08
LFDBF:  lda $05
        clc
        bmi ++
        beq SecExit
        adc $09
        bcc +
        ldy $02
        beq ClcExit2
        inc $0B
*       jmp ++

*       adc $09
        bcs +
        ldy $02
        beq ClcExit2
        inc $0B
*       sta $09
        SecExit:
        sec
        rts

        ClcExit2:
        clc
*       rts

UpdateTourianItems:
; Adds mother brain and zebetite 
LFDE3:  lda EndTimerHi          ; Determine if this is the first frame the end timer is running
        cmp #$99                ; (it will have a value of 99.99 the first frame)
        bne +                   
        clc                     
        sbc EndTimerLo          
        bne +                   ; On the first frame of the end timer:
                                
        sta $06	                ; 
        lda #$38                ;
        sta $07                 ;    Add [mother brain defeated] to item history
        jsr LDC54               ; 
                                
*       ldx #$20                ; Loop through zebetites (@ x = 20, 18, 10, 8, 0)
*       jsr CheckZebetite       ;     ($FE05) Update one zebetite
        txa                     ;     (Subtract 8 from x)
        sec                     
        sbc #$08                
        tax                     
        bne -                   
                                
CheckZebetite                   
LFE05:  lda $0758,x             ; 
        sec                     
        sbc #$02                ; 
        bne ---                 ; Exit if zebetite state != 2
        sta $06                 ; Store 0 to $06
        inc $0758,x             ; Set zebetite state to 3
        txa                     
        lsr                     ; A =  zebetite index * 4 (10, C, 8, 4, or 0)
        adc #$3C                ;      + $3C
        sta $07                 
        jmp LDC54               ; Add zebetite to item history

; Tile degenerate/regenerate

UpdateTiles:
        ldx #$C0
*       jsr DoOneTile
        ldx PageIndex
        jsr Xminus16
        bne -
        DoOneTile:
        stx PageIndex
        lda TileRoutine,x
        beq +          ; exit if tile not active
        jsr ChooseRoutine

; Pointer table to code

        .word ExitSub       ;($C45C) rts
        .word $FE3D
        .word $FE54
        .word $FE59
        .word $FE54
        .word $FE83

LFE3D:  inc TileRoutine,x
        lda #$00
        jsr SetTileAnim
        lda #$50
        sta TileDelay,x
        lda TileWRAMLo,x     ; low WRAM addr of blasted tile
        sta $00
        lda TileWRAMHi,x     ; high WRAM addr
        sta $01

LFE54:  lda #$02
        jmp UpdateTileAnim

LFE59:  lda FrameCount
        and #$03
        bne +       ; only update tile timer every 4th frame
        dec TileDelay,x
        bne +       ; exit if timer not reached zero
        inc TileRoutine,x
        ldy TileType,x
        lda Table19,y
        SetTileAnim:
        sta TileAnimIndex,x
        sta $0505,x
        lda #$00
        sta TileAnimDelay,x
*       rts

; Table used for indexing the animations in TileBlastAnim (see below)

Table19:
        .byte $18,$1C,$20,$00,$04,$08,$0C,$10,$24,$14

LFE83:  lda #$00
        sta TileRoutine,x       ; tile = respawned
        lda TileWRAMLo,x
        clc
        adc #$21
        sta $00
        lda TileWRAMHi,x
        sta $01
        jsr LFF3C
        lda $02
        sta $07
        lda $03
        sta $09
        lda $01
        lsr
        lsr
        and #$01
        sta $0B
        ldy #$00
        jsr LF186
        lda #$04
        clc
        adc ObjRadY
        sta $04
        lda #$04
        clc
        adc ObjRadX
        sta $05
        jsr LF1FA
        bcs Exit23
        jsr LF311
        lda #$50
        sta HealthLoChange
        jmp SubtractHealth              ;($CE92)

        GetTileFramePtr:
        lda TileAnimFrame,x
        asl
        tay
        lda $97AF,y
        sta $02
        lda $97B0,y
        sta $03
Exit23: rts

        DrawTileBlast:
        lda PPUStrIndex
        cmp #$1F
        bcs Exit23
        ldx PageIndex
        lda TileWRAMLo,x
        sta $00
        lda TileWRAMHi,x
        sta $01
        jsr GetTileFramePtr
        ldy #$00
        sty $11
        lda ($02),y
        tax
        jsr Adiv16       ; / 16
        sta $04
        txa
        and #$0F
        sta $05
        iny
        sty $10
*       ldx $05
*       ldy $10
        lda ($02),y
        inc $10
        ldy $11
        sta ($00),y
        inc $11
        dex
        bne -
        lda $11
        clc
        adc #$20
        sec
        sbc $05
        sta $11
        dec $04
        bne --
        lda $01
        and #$04
        beq +
        lda $01
        ora #$0C
        sta $01
*       lda $01
        and #$2F
        sta $01
        jsr LC328
        clc
        rts

LFF3C:  lda $00
        tay
        and #$E0
        sta $02
        lda $01
        lsr
        ror $02
        lsr
        ror $02
        tya
        and #$1F
        jsr Amul8       ; * 8
        sta $03
        rts

UpdateTileAnim:
        ldx PageIndex
        ldy TileAnimDelay,x
        beq +
        dec TileAnimDelay,x
        bne ++
*       sta TileAnimDelay,x
        ldy TileAnimIndex,x
        lda TileBlastAnim,y
        cmp #$FE            ; end of "tile-blast" animation?
        beq ++
        sta TileAnimFrame,x
        iny
        tya
        sta TileAnimIndex,x
        jsr DrawTileBlast
        bcc +
        ldx PageIndex
        dec TileAnimIndex,x
*       rts

*       inc TileRoutine,x
        pla
        pla
        rts

; Frame data for tile blasts

        TileBlastAnim:
        .byte $06,$07,$00,$FE
        .byte $07,$06,$01,$FE
        .byte $07,$06,$02,$FE
        .byte $07,$06,$03,$FE
        .byte $07,$06,$04,$FE
        .byte $07,$06,$05,$FE
        .byte $07,$06,$09,$FE
        .byte $07,$06,$0A,$FE
        .byte $07,$06,$0B,$FE
        .byte $07,$06,$08,$FE

        .byte $00
        .byte $00

;-----------------------------------------------[ RESET ]--------------------------------------------

RESET:
LFFB0:  SEI                             ;Disables interrupt
LFFB1:  CLD                             ;Sets processor to binary mode
LFFB2:  LDX #$00                        ;
LFFB4:  STX PPUControl0                 ;Clear PPU control registers
LFFB7:  STX PPUControl1                 ;
LFFBA:* LDA PPUStatus                   ;
LFFBD:  BPL -                           ;Wait for VBlank
LFFBF:* LDA PPUStatus                   ;
LFFC2:  BPL -                           ;
LFFC4:  ORA #$FF                        ;
LFFC6:  STA MMC1Reg0                    ;Reset MMC1 chip
LFFC9:  STA MMC1Reg1                    ;(MSB is set)
LFFCC:  STA MMC1Reg2                    ;
LFFCF:  STA MMC1Reg3                    ;
LFFD2:  JMP Startup                     ;($C01A)Do preliminary housekeeping.

;Not used.
LFFD5:  .byte $FF, $FF, $FF, $4C, $E4, $B3, $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF
LFFE5:  .byte $FF, $FF, $FF, $FF, $4D, $45, $54, $52, $4F, $49, $44, $E4, $8D, $00, $00, $38
LFFF5:  .byte $04, $01, $06, $01, $BC

;-----------------------------------------[ Interrupt vectors ]--------------------------------------

LBFFA:  .word NMI                       ;($C0D9)NMI vector.
LBFFC:  .word RESET                     ;($FFB0)Reset vector.
LBFFE:  .word RESET                     ;($FFB0)IRQ vector.
metroid/disassembly/game_engine_page.txt · Last modified: 2016/03/06 12:29 by snarfblam