MyScrollingASM

.inesprg 1   ; 1x 16KB PRG code
  .ineschr 1   ; 1x  8KB CHR data
  .inesmap 0   ; mapper 0 = NROM, no bank swapping
  .inesmir 1   ; VERT mirroring for HORIZ scrolling


;;;;;;;;;;;;;;;

;; DECLARE SOME VARIABLES HERE
  .rsset $0000  ;;start variables at ram location 0

scroll          .rs 1  ; horizontal scroll count
nametable       .rs 1  ; which nametable to use, 0 or 1
columnLow       .rs 1  ; low byte of new column address
columnHigh      .rs 1  ; high byte of new column address
sourceLow       .rs 1  ; source for column data
sourceHigh      .rs 1
columnNumber    .rs 1  ; which column of level data to draw

partialVariable .rs 1  ; fractional walking speed
isLeft          .rs 1  ; set if facing left
isDescending    .rs 1  ; set if descending
isOnGround:     .rs 1  ; set if on ground

;; DECLARE SOME CONSTANTS HERE

GROUND      = $C8
SEMIGROUND  = $C0
TOP_JUMP    = $80

MARIO       = $0200

;;;;;;;;;;;;

  .bank 0
  .org $C000
RESET:
  SEI          ; disable IRQs
  CLD          ; disable decimal mode
  LDX #$40
  STX $4017    ; disable APU frame IRQ
  LDX #$FF
  TXS          ; Set up stack
  INX          ; now X = 0
  STX $2000    ; disable NMI
  STX $2001    ; disable rendering
  STX $4010    ; disable DMC IRQs

vblankwait1:       ; First wait for vblank to make sure PPU is ready
  BIT $2002
  BPL vblankwait1

clrmem:
  LDA #$00
  STA $0000, x
  STA $0100, x
  STA $0300, x
  STA $0400, x
  STA $0500, x
  STA $0600, x
  STA $0700, x
  LDA #$FE
  STA $0200, x
  INX
  BNE clrmem

vblankwait2:      ; Second wait for vblank, PPU is ready after this
  BIT $2002
  BPL vblankwait2


LoadPalettes:
  LDA $2002             ; read PPU status to reset the high/low latch
  LDA #$3F
  STA $2006             ; write the high byte of $3F00 address
  LDA #$00
  STA $2006             ; write the low byte of $3F00 address
  LDX #$00              ; start out at 0
LoadPalettesLoop:
  LDA palette, x        ; load data from address (palette + the value in x)
  STA $2007             ; write to PPU
  INX                   ; X = X + 1
  CPX #$20              ; Compare X to hex $10, decimal 16 - copying 16 bytes = 4 sprites
  BNE LoadPalettesLoop  ; Branch to LoadPalettesLoop if compare was Not Equal to zero
                        ; if compare was equal to 32, keep going down


LoadSprites:
  LDX #$00              ; start at 0
LoadSpritesLoop:
  LDA sprites, x        ; load data from address (sprites +  x)
  STA $0200, x          ; store into RAM address ($0200 + x)
  INX                   ; X = X + 1
  CPX #$10              ; Compare X to hex $20, decimal 16
  BNE LoadSpritesLoop   ; Branch to LoadSpritesLoop if compare was Not Equal to zero
                        ; if compare was equal to 16, keep going down


InitializeNametables:
  LDA #$01
  STA nametable
  LDA #$00
  STA scroll
  STA columnNumber
InitializeNametablesLoop:
  JSR DrawNewColumn     ; draw bg column
  LDA scroll            ; go to next column
  CLC
  ADC #$08
  STA scroll
  INC columnNumber
  LDA columnNumber      ; repeat for first nametable
  CMP #$20
  BNE InitializeNametablesLoop

  LDA #$00
  STA nametable
  LDA #$00
  STA scroll
  JSR DrawNewColumn     ; draw first column of second nametable
  INC columnNumber

  LDA #$00              ; set back to increment +1 mode
  STA $2000
InitializeNametablesDone:


InitializeAttributes:
  LDA #$01
  STA nametable
  LDA #$00
  STA scroll
  STA columnNumber
InitializeAttributesLoop:
  JSR DrawNewAttributes     ; draw attribs
  LDA scroll                ; go to next column
  CLC
  ADC #$20
  STA scroll

  LDA columnNumber      ; repeat for first nametable
  CLC
  ADC #$04
  STA columnNumber
  CMP #$20
  BNE InitializeAttributesLoop

  LDA #$00
  STA nametable
  LDA #$00
  STA scroll
  JSR DrawNewAttributes     ; draw first column of second nametable
InitializeAttributesDone:

  LDA #$21
  STA columnNumber


  LDA #%10010000   ; enable NMI, sprites from Pattern Table 0, background from Pattern Table 1
  STA $2000

  LDA #%00011110    ; enable sprites, enable background, no clipping on left side
  STA $2001


  ;; ----- Initialize variables -----
  LDA #$00
  STA partialVariable

  LDA #%00000000
  STA isLeft

  LDA #%00000000
  STA isDescending

  LDA #%00000001
  STA isOnGround

Forever:
  JMP Forever       ; jump back to Forever, infinite loop


  ;; ----- NMI -----

NMI:

  LDA #$00
  STA $2003
  LDA #$02
  STA $4014       ; sprite DMA from $0200

  ; run other game graphics updating code here

  LDA #$00
  STA $2006        ; clean up PPU address registers
  STA $2006

  LDA scroll
  STA $2005        ; write the horizontal scroll count register

  LDA #$00         ; no vertical scrolling
  STA $2005


  ;; ------------------------------------------------------------------------------
  ;; This is the PPU clean up section, so rendering the next frame starts properly.
  ;; ------------------------------------------------------------------------------

  LDA #%10010000   ; enable NMI, sprites from Pattern Table 0, background from Pattern Table 1
  ORA nametable    ; select correct nametable for bit 0
  STA $2000

  LDA #%00011110   ; enable sprites, enable background, no clipping on left side
  STA $2001

  ; run normal game engine code here
  ; reading from controllers, etc

  ;; --------------------------------
  ;; ---------- CONTROLLER ----------
  ;; --------------------------------

  LatchController:
  LDA #$01
  STA $4016
  LDA #$00
  STA $4016         ;  tell both the controllers to latch buttons

ReadA:              ; ----- BUTTON A (JUMP) -----
  LDA $4016         ; player 1 - A
  AND #%00000001    ; only look at bit 0
  BEQ DescendNow    ; branch to DescendNow if button is NOT pressed (0)
                    ; add instructions here to do something when button IS pressed (1)

  LDA MARIO
  CMP #TOP_JUMP
  BEQ DescendNow

  LDA isDescending
  CMP #%00000001
  BEQ DescendNow

  JSR Jump
  LDA #$00
  CMP #$00
  BEQ ReadADone     ; branch always

DescendNow:
  LDA MARIO
  CMP #SEMIGROUND
  BEQ JumpDescend

  LDA #%00000001
  STA isDescending

JumpDescend:
  JSR Descend

ReadADone:          ; handling this button is done


ReadB:
  LDA $4016       ; player 1 - B
  AND #%00000001  ; only look at bit 0
  BEQ ReadBDone   ; branch to ReadBDone if button is NOT pressed (0)
                  ; add instructions here to do something when button IS pressed (1)

ReadBDone:        ; handling this button is done


ReadSelect:
  LDA $4016
  AND #%00000001
  BEQ ReadSelectDone

ReadSelectDone:


ReadStart:
  LDA $4016
  AND #$00000001
  BEQ ReadStartDone

ReadStartDone:


ReadUp:
  LDA $4016
  AND #$00000001
  BEQ ReadUpDone

ReadUpDone:


ReadDown:
  LDA $4016
  AND #%00000001
  BEQ ReadDownDone

ReadDownDone:


ReadLeft:               ; ----- LEFT BUTTON -----
  LDA $4016
  AND #%00000001
  BEQ NotWalkingLeft

  LDA #%00000001
  STA isLeft            ; left

  LDA #$33              ; load walking sprites
  STA $0201
  LDA #$32
  STA $0205
  LDA #$43
  STA $0209
  LDA #$42
  STA $020D

  LDA #%01000000       ; unflip
  STA $0202
  STA $0206
  STA $020A
  STA $020E

  LDA isOnGround
  CMP #%00000001
  BEQ OnGroundLeft

  LDA #$41              ; load jumping sprites
  STA $0201
  LDA #$32
  STA $0205
  LDA #$43
  STA $0209
  LDA #$42
  STA $020D
  LDA #%01000000
  STA $0202
  STA $0206
  STA $020A
  STA $020E

OnGroundLeft:
  LDX #$03
  LDY partialVariable

ButtonLeftLoop:
  TYA
  SEC
  SBC #$20              ; fractionary speed
  STA partialVariable
  LDA MARIO, X          ; load sprite X position
  SBC #$01              ; integer speed
  STA MARIO, X          ; save sprite X position
  INX
  INX
  INX
  INX
  CPX #$13
  BNE ButtonLeftLoop

  LDA #$00
  CMP #$00
  BEQ ReadLeftDone      ; branch always

NotWalkingLeft:         ; only when on ground and left

  LDA isOnGround
  CMP #%00000001
  BNE ReadLeftDone

  LDA isLeft
  CMP #%00000001
  BNE ReadLeftDone

  LDA #$33              ; load static left sprites
  STA $0201
  LDA #$32
  STA $0205
  LDA #$4F
  STA $0209
  STA $020D

  LDA #%0000000       ; flip
  STA $020A
  LDA #%01000000
  STA $0202
  STA $0206
  STA $020E

ReadLeftDone:


ReadRight:              ; ----- RIGHT BUTTON -----
  LDA $4016
  AND #$00000001
  BEQ NotWalkingRight

  ; background scrolling
  JSR Scrolling

  ; MARIO ACTIONS

  LDA #%00000000
  STA isLeft            ; not left

  LDA #$32              ; load walking sprites
  STA $0201
  LDA #$33
  STA $0205
  LDA #$42
  STA $0209
  LDA #$43
  STA $020D

  LDA #%00000000       ; unflip
  STA $0202
  STA $0206
  STA $020A
  STA $020E

  LDA isOnGround
  CMP #%00000001
  BEQ OnGroundRight

  LDA #$32              ; load jumping sprites
  STA $0201
  LDA #$41
  STA $0205
  LDA #$42
  STA $0209
  LDA #$43
  STA $020D
  LDA #%00000000
  STA $0202
  STA $0206
  STA $020A
  STA $020E


OnGroundRight:
  LDX #$03
  LDY partialVariable

ButtonRightLoop:
  TYA
  CLC
  ADC #$20              ; fractionary speed
  STA partialVariable
  LDA MARIO, X          ; load sprite X position
  ADC #$01              ; integer speed
  STA MARIO, X          ; save sprite X position
  INX
  INX
  INX
  INX
  CPX #$13
  BNE ButtonRightLoop

  LDA #$00
  CMP #$00
  BEQ ReadRightDone     ; branch always


NotWalkingRight:        ; only when on ground and not left

  LDA isOnGround
  CMP #%00000001
  BNE ReadRightDone

  LDA isLeft
  CMP #%00000001
  BEQ ReadRightDone

  LDA #$32              ; load static sprites
  STA $0201
  LDA #$33
  STA $0205
  LDA #$4F
  STA $0209
  STA $020D

  LDA #%00000000       ; unflip
  STA $0202
  STA $0206
  STA $020A
  LDA #%01000000
  STA $020E

ReadRightDone:

  RTI              ; return from interrupt


  ;; ---------------------------------
  ;; ---------- SUBROUTINES ----------
  ;; ---------------------------------

  ;; ----- SCROLLING -----

Scrolling:

  INC scroll

NTSwapCheck:
  LDA scroll            ; check if the scroll just wrapped from 255 to 0
  BNE NTSwapCheckDone
NTSwap:
  LDA nametable         ; load current nametable number (0 or 1)
  EOR #$01              ; exclusive OR of bit 0 will flip that bit
  STA nametable         ; so if nametable was 0, now 1
                        ;    if nametable was 1, now 0
NTSwapCheckDone:

NewAttribCheck:
  LDA scroll
  AND #%00011111            ; check for multiple of 32
  BNE NewAttribCheckDone    ; if low 5 bits = 0, time to write new attribute bytes
  jsr DrawNewAttributes
NewAttribCheckDone:

NewColumnCheck:
  LDA scroll
  AND #%00000111            ; throw away higher bits to check for multiple of 8
  BNE NewColumnCheckDone    ; done if lower bits != 0
  JSR DrawNewColumn         ; if lower bits = 0, time for new column

  lda columnNumber
  clc
  adc #$01             ; go to next column
  and #%01111111       ; only 128 columns of data, throw away top bit to wrap
  sta columnNumber
NewColumnCheckDone:

  RTS

DrawNewColumn:
  LDA scroll       ; calculate new column address using scroll register
  LSR A
  LSR A
  LSR A            ; shift right 3 times = divide by 8
  STA columnLow    ; $00 to $1F, screen is 32 tiles wide

  LDA nametable     ; calculate new column address using current nametable
  EOR #$01          ; invert low bit, A = $00 or $01
  ASL A             ; shift up, A = $00 or $02
  ASL A             ; $00 or $04
  CLC
  ADC #$20          ; add high byte of nametable base address ($2000)
  STA columnHigh    ; now address = $20 or $24 for nametable 0 or 1

  LDA columnNumber  ; column number * 32 = column data offset
  ASL A
  ASL A
  ASL A
  ASL A
  ASL A
  STA sourceLow
  LDA columnNumber
  LSR A
  LSR A
  LSR A
  STA sourceHigh

  LDA sourceLow       ; column data start + offset = address to load column data from
  CLC
  ADC #LOW(columnData)
  STA sourceLow
  LDA sourceHigh
  ADC #HIGH(columnData)
  STA sourceHigh

DrawColumn:
  LDA #%00000100        ; set to increment +32 mode
  STA $2000

  LDA $2002             ; read PPU status to reset the high/low latch
  LDA columnHigh
  STA $2006             ; write the high byte of column address
  LDA columnLow
  STA $2006             ; write the low byte of column address
  LDX #$1E              ; copy 30 bytes
  LDY #$00
DrawColumnLoop:
  LDA [sourceLow], y
  STA $2007
  INY
  DEX
  BNE DrawColumnLoop

  RTS


DrawNewAttributes:
  LDA nametable
  EOR #$01          ; invert low bit, A = $00 or $01
  ASL A             ; shift up, A = $00 or $02
  ASL A             ; $00 or $04
  CLC
  ADC #$23          ; add high byte of attribute base address ($23C0)
  STA columnHigh    ; now address = $23 or $27 for nametable 0 or 1

  LDA scroll
  LSR A
  LSR A
  LSR A
  LSR A
  LSR A
  CLC
  ADC #$C0
  STA columnLow     ; attribute base + scroll / 32

  LDA columnNumber  ; (column number / 4) * 8 = column data offset
  AND #%11111100
  ASL A
  STA sourceLow
  LDA columnNumber
  LSR A
  LSR A
  LSR A
  LSR A
  LSR A
  LSR A
  LSR A
  STA sourceHigh

  LDA sourceLow       ; column data start + offset = address to load column data from
  CLC
  ADC #LOW(attribData)
  STA sourceLow
  LDA sourceHigh
  ADC #HIGH(attribData)
  STA sourceHigh

  LDY #$00
  LDA $2002             ; read PPU status to reset the high/low latch
DrawNewAttributesLoop
  LDA columnHigh
  STA $2006             ; write the high byte of column address
  LDA columnLow
  STA $2006             ; write the low byte of column address
  LDA [sourceLow], y    ; copy new attribute byte
  STA $2007

  INY
  CPY #$08              ; copy 8 attribute bytes
  BEQ DrawNewAttributesLoopDone

  LDA columnLow         ; next attribute byte is at address + 8
  CLC
  ADC #$08
  STA columnLow
  JMP DrawNewAttributesLoop
DrawNewAttributesLoopDone:

  RTS


  ;; ----- MARIO ACTIONS -----

Jump:

  LDA #%00000000
  STA isOnGround        ; false

  LDA #$32              ; load right sprites
  STA $0201
  LDA #$41
  STA $0205
  LDA #$42
  STA $0209
  LDA #$43
  STA $020D
  LDA #%00000000
  STA $0202
  STA $0206
  STA $020A
  STA $020E

  LDA isLeft
  CMP #%00000001
  BNE NotLeft

  LDA #$41              ; load left sprites
  STA $0201
  LDA #$32
  STA $0205
  LDA #$43
  STA $0209
  LDA #$42
  STA $020D
  LDA #%01000000
  STA $0202
  STA $0206
  STA $020A
  STA $020E

NotLeft:
  LDA MARIO
  CMP #TOP_JUMP
  BEQ Return

  LDX #$00
SpriteUpLoop:
  LDA MARIO, x    ; load sprite Y position
  SEC             ; make sure carry flag is set
  SBC #$02        ; jump speed
  STA MARIO, x    ; save sprite Y position
  INX
  INX
  INX
  INX
  CPX #$10
  BNE SpriteUpLoop

Return:
  RTS


Descend:

  LDA isOnGround
  CMP #%00000001
  BEQ DescendReturn

StepDown:
  LDX #$00
SpriteDownLoop:
  LDA MARIO, x    ; load sprite Y position
  CLC             ; make sure carry flag is clear
  ADC #$02        ; descend speed
  STA MARIO, x    ; save sprite Y position
  INX
  INX
  INX
  INX
  CPX #$10
  BNE SpriteDownLoop
  ;JSR vblankwait

  LDA MARIO
  CMP #SEMIGROUND
  BNE DescendReturn

  JSR OnGround

DescendReturn
  RTS


OnGround:
  LDA #%00000001
  STA isOnGround        ; true

  LDA #%00000000
  STA isDescending      ;false

  LDA #$32              ; restore right sprites
  STA $0201
  LDA #$33
  STA $0205
  LDA #$4F
  STA $0209
  STA $020D
  LDA #%00000000
  STA $0202
  STA $0206
  STA $020A
  LDA #%01000000
  STA $020E

  LDA isLeft
  CMP #%00000001
  BNE NotDescending

  LDA #$33              ; restore left sprites
  STA $0201
  LDA #$32
  STA $0205
  LDA #$4F
  STA $0209
  STA $020D
  LDA #%01000000
  STA $0202
  STA $0206
  STA $020E
  LDA #%00000000
  STA $020A

NotDescending:
  LDA #%00000000
  STA isDescending
  RTS


;;;;;;;;;;;;;;

  .bank 1
  .org $E000
palette:
  .db $22,$29,$1A,$0F,  $22,$36,$17,$0F,  $22,$30,$21,$0F,  $22,$27,$17,$0F   ;;background palette
  .db $22,$16,$27,$18,  $22,$1A,$30,$27,  $22,$16,$30,$27,  $22,$0F,$36,$17   ;;sprite palette

sprites:
     ;vert        tile attr horiz
  .db SEMIGROUND, $32, $00, $40   ;sprite 0
  .db SEMIGROUND, $33, $00, $48   ;sprite 1
  .db GROUND,     $4F, $00, $40   ;sprite 2
  .db GROUND,     $4F, $40, $48   ;sprite 3


columnData:
  .incbin "SMBlevel.bin"

attribData:
  .incbin "SMBattrib.bin"

  .org $FFFA     ;first of the three vectors starts here
  .dw NMI        ;when an NMI happens (once per frame if enabled) the
                   ;processor will jump to the label NMI:
  .dw RESET      ;when the processor first turns on or is reset, it will jump
                   ;to the label RESET:
  .dw 0          ;external interrupt IRQ is not used in this tutorial


;;;;;;;;;;;;;;


  .bank 2
  .org $0000
  .incbin "mario.chr"   ;includes 8KB graphics file from SMB1