.MEMORYMAP DEFAULTSLOT 0 SLOTSIZE $4000 SLOT 0 $C000 SLOTSIZE $2000 SLOT 1 $0000 ; location doesn't matter, CHR data isn't in main memory .ENDME .ROMBANKMAP BANKSTOTAL 2 BANKSIZE $4000 BANKS 1 BANKSIZE $2000 BANKS 1 .ENDRO .enum $0000 buttons_pressed DB current_state DB sprite_x DB sprite_y DB .ende .bank 0 .org $0000 ; the ppu takes two frames to initialize, so we have some time to do whatever ; initialization of our own that we want to while we wait. we choose here to ; set up cpu flags in the first frame and clear out system ram in the second ; frame (clearing out ram isn't at all necessary, but we can't do anything ; useful at this point anyway, so we may as well in order to make things more ; predictable). clearing out system ram actually takes quite a bit longer than ; a frame (a frame is ~2273 cycles, or ~324-1136 opcodes), but we may as well ; start the process while we wait. RESET: SEI ; disable IRQs CLD ; disable decimal mode LDX #$40 STX $4017.w ; disable APU frame IRQ LDX #$FF TXS ; Set up stack (grows down from $FF to $00, at $0100-$01FF) INX ; now X = 0 STX $2000.w ; disable NMI (we'll enable it later once the ppu is ready) STX $2001.w ; disable rendering (same) STX $4010.w ; disable DMC IRQs vblankwait1: ; First wait for vblank to make sure PPU is ready BIT $2002 ; bit 7 of $2002 is reset once vblank ends BPL vblankwait1 ; and bit 7 is what is checked by BPL ; set everything in ram ($0000-$07FF) to $00, except for $0200-$02FF which ; is conventionally used to hold sprite attribute data. we set that range ; to $FE, since that value as a position moves the sprites offscreen, and ; when the sprites are offscreen, it doesn't matter which sprites are ; selected or what their attributes are 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 ; initialize variables in ram LDA #$00 STA buttons_pressed STA current_state LDA #$80 STA sprite_x STA sprite_y LDA #$32 STA $0201 ; set the sprite number to display LDA #$00 STA $0202 ; set the sprite attributes (palette, flipping, etc) LDA #$33 STA $0205 ; set the sprite number to display LDA #$00 STA $0206 ; set the sprite attributes (palette, flipping, etc) LDA #$34 STA $0209 ; set the sprite number to display LDA #$00 STA $020A ; set the sprite attributes (palette, flipping, etc) LDA #$35 STA $020D ; set the sprite number to display LDA #$00 STA $020E ; set the sprite attributes (palette, flipping, etc) vblankwait2: ; Second wait for vblank, PPU is ready after this BIT $2002 BPL vblankwait2 ; now that the ppu is ready, we can start initializing it 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 LoadPalettesLoop: LDA palette.w, x ;load palette byte STA $2007 ;write to PPU INX ;set index to next byte CPX #$20 BNE LoadPalettesLoop ;if x = $20, 32 bytes copied, all done LDA #%00010000 ; enable sprites STA $2001 LDA #%10000000 ; enable NMI interrupts STA $2000 loop: JMP loop read_controller1: ; latch LDA #$01 STA $4016 LDA #$00 STA $4016 ; clock LDX #$00 read_controller1_values: CPX #$08 BPL end_read_controller1 LDA $4016 AND #%00000001 ASL buttons_pressed ORA buttons_pressed STA buttons_pressed INX JMP read_controller1_values end_read_controller1: RTS turn_blue: LDA #%10010000 STA $2001 LDA #$00 STA current_state RTS turn_green: LDA #%01010000 STA $2001 LDA #$01 STA current_state RTS turn_red: LDA #%00110000 STA $2001 LDA #$02 STA current_state RTS NMI: JSR read_controller1 handle_up: LDA buttons_pressed AND #%00001000 CMP #$00 BEQ handle_down LDY sprite_y DEY STY sprite_y handle_down: LDA buttons_pressed AND #%00000100 CMP #$00 BEQ handle_left LDY sprite_y INY STY sprite_y handle_left: LDA buttons_pressed AND #%00000010 CMP #$00 BEQ handle_right LDY sprite_x DEY STY sprite_x handle_right: LDA buttons_pressed AND #%00000001 CMP #$00 BEQ handle_a LDY sprite_x INY STY sprite_x handle_a: LDA buttons_pressed AND #%10000000 CMP #$00 BEQ nmi_return LDY current_state CPY #$00 BEQ call_turn_green CPY #$01 BEQ call_turn_red call_turn_blue: JSR turn_blue JMP nmi_return call_turn_green: JSR turn_green JMP nmi_return call_turn_red: JSR turn_red JMP nmi_return nmi_return: ; update the sprite locations LDA sprite_y STA $0200 LDA sprite_x STA $0203 LDA sprite_y STA $0204 LDA sprite_x ADC #$07 ; XXX why is this #$07 instead of #$08? STA $0207 LDA sprite_y ADC #$08 STA $0208 LDA sprite_x STA $020B LDA sprite_y ADC #$08 STA $020C LDA sprite_x ADC #$08 STA $020F ; load the sprite into the ppu ports (from $0200) LDA #$00 STA $2003 LDA #$02 STA $4014 RTI palette: .db $0F,$31,$32,$33,$0F,$35,$36,$37,$0F,$39,$3A,$3B,$0F,$3D,$3E,$0F .db $0F,$1C,$15,$14,$0F,$02,$38,$3C,$0F,$1C,$15,$14,$0F,$02,$38,$3C .orga $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 1 slot 1 .org $0000 .incbin "mario.chr"