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.MEMORYMAP
SLOTSIZE $2000
DEFAULTSLOT 0
SLOT 0 $8000
SLOT 1 $E000
SLOT 2 $6000
.ENDME
.ROMBANKMAP
BANKSTOTAL 2
BANKSIZE $2000
BANKS 2
.ENDRO
.bank 0
.org $0000
RESET:
SEI ; disable IRQs
CLD ; disable decimal mode
LDX #$40
STX $4017.W ; disable APU frame IRQ
LDX #$FF
TXS ; Set up stack
INX ; now X = 0
STX $2000.W ; disable NMI
STX $2001.W ; disable rendering
STX $4010.W ; 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 $0200, x
STA $0400, x
STA $0500, x
STA $0600, x
STA $0700, x
LDA #$FE
STA $0300, x
INX
BNE clrmem
vblankwait2: ; Second wait for vblank, PPU is ready after this
BIT $2002
BPL vblankwait2
LDA #%10000000 ;intensify blues
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.w
ORA buttons_pressed.w
STA buttons_pressed.w
INX
JMP read_controller1_values
end_read_controller1:
RTS
turn_blue:
LDA #%10000000
STA $2001
LDA #$00
STA current_state.w
RTS
turn_green:
LDA #%01000000
STA $2001
LDA #$01
STA current_state.w
RTS
turn_red:
LDA #%00100000
STA $2001
LDA #$02
STA current_state.w
RTS
NMI:
JSR read_controller1
; if A is not pressed, return
LDA buttons_pressed.w
AND #%10000000
CMP #$00
BEQ loop
LDY current_state.w
CPY #$00
BEQ call_turn_green
CPY #$01
BEQ call_turn_red
call_turn_blue:
JSR turn_blue
JMP color_set
call_turn_green:
JSR turn_green
JMP color_set
call_turn_red:
JSR turn_red
JMP color_set
color_set:
RTI
.bank 1 slot 1
.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 2
.org $0000
buttons_pressed: .ds 1, $00
current_state: .ds 1, $00
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