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; INES header stuff
.inesprg 1 ; 1 bank of PRG
.ineschr 1 ; 1 bank of CHR data
.inesmir 0 ; mirroring
.inesmap 0 ; we use mapper 0
.rsset $0000 ; variables
COPY_SOURCE_ADDR .rs 2
COPY_DEST_ADDR .rs 2
.rsset $0200
SPRITES .rs 256
.bank 1
.org $FFFA ; reset vectors
.dw NMI
.dw Start
.dw IRQ
.bank 0
.org $C000 ; code starts here
Start:
; disable interrupts
sei
; reset stack
ldx #$ff
txs
; disable PPU
lda #%00000000
sta PPUCTRL
lda #%00000000
sta PPUMASK
jsr waitblank
; reset sound
lda #0
sta $4000
sta $4001
sta $4002
sta $4003
sta $4004
sta $4005
sta $4006
sta $4007
sta $4009
sta $400A
sta $400C
sta $400D
sta $400E
sta $400F
sta $4010
sta $4011
sta $4012
sta $4013
lda #$0F
sta $4015
lda #$40
sta $4017
lda #0
load_palette:
; load single palette for sprites
lda #$3F
sta PPUADDR
lda #$10
sta PPUADDR
lda palette
sta PPUDATA
lda palette+1
sta PPUDATA
lda palette+2
sta PPUDATA
lda palette+3
sta PPUDATA
reset_sprites:
lda #$FF
ldx 0
.loop:
sta SPRITES, x
inx
bne .loop
set_sprites:
ldx 0
.loop:
lda sprites_init_data, x
sta SPRITES, x
inx
cpx #(4 * 8)
bne .loop
; enable PPU
jsr waitblank
lda #%00100000
sta PPUCTRL
lda #%00010100
sta PPUMASK
main_loop:
jsr waitblank
ldx 0
.move_sprites_loop:
inc SPRITES, x
inx
inx
inx
inx
cpx #(4 * 12 + 3)
bne .move_sprites_loop
lda #0
sta OAMADDR
lda #HIGH(SPRITES)
sta OAMDMA
jmp main_loop
; VBlank wait subroutine
waitblank:
bit PPUSTATUS
lda #0
sta PPUSCROLL
sta PPUSCROLL
.loop:
lda PPUSTATUS ; load A with value at location PPUSTATUS
bpl .loop ; if bit 7 is not set (not VBlank) keep checking
rts
NMI:
rti
IRQ:
rti
palette:
.incbin "palette_0.bin"
sprites_init_data:
.db 20, 0, 0, 0
.db 20, 2, 0, 8
.db 80, 4, 0, 30
.db 80, 6, 0, 38
.db 120, 8, 0, 60
.db 120, 10, 0, 68
.db 180, 12, 0, 90
.db 180, 14, 0, 98
.bank 2
.org $0000
.incbin "pattern_0.bin"
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