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; INES header stuff
.inesprg 1 ; 1 bank of PRG
.ineschr 1 ; 1 bank of CHR data
.inesmir 1 ; mirroring
.inesmap 0 ; we use mapper 0
DELAY .equ 2
.rsset $0000 ; variables
COPY_SOURCE_ADDR .rs 2
COPY_DEST_ADDR .rs 2
SCROLL_X .rs 1
PAUSE .rs 1
DIR .rs 1
.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:
lda #LOW(palette)
sta <COPY_SOURCE_ADDR
lda #HIGH(palette)
sta <COPY_SOURCE_ADDR+1
lda #$3F
sta PPUADDR
lda #$00
sta PPUADDR
ldy #$00
ldx #16
.loop:
lda [COPY_SOURCE_ADDR], y
sta PPUDATA
iny
dex
bne .loop
load_nametable:
lda #LOW(nametable_0)
sta <COPY_SOURCE_ADDR
lda #HIGH(nametable_0)
sta <COPY_SOURCE_ADDR+1
lda #$20
sta PPUADDR
lda #$00
sta PPUADDR
ldy #$00
ldx #$00
.loop:
lda [COPY_SOURCE_ADDR], y
sta PPUDATA
iny
bne .loop
inc COPY_SOURCE_ADDR+1
inx
cpx #8
bne .loop
; enable PPU
jsr waitblank
lda #%00001010
sta PPUMASK
lda #%00000000
sta PPUCTRL
; reset variables
lda #0
sta SCROLL_X
sta DIR
main_loop:
jsr waitblank
jmp main_loop
; VBlank wait subroutine
waitblank:
bit PPUSTATUS
ldx SCROLL_X
stx PPUSCROLL
inc PAUSE
lda PAUSE
cmp #DELAY
bne .scroll
lda #0
sta PAUSE
lda DIR
bne .left
inx
bne .scroll
lda #1
sta DIR
dex
jmp .scroll
.no_turn_left:
jmp .scroll
.left:
dex
bne .scroll
lda #0
sta DIR
.scroll:
stx SCROLL_X
lda #0
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
nametable_0:
.incbin "name_table_0.bin"
attr_table_0:
.incbin "attr_table_0.bin"
nametable_1:
.incbin "name_table_1.bin"
attr_table_1:
.incbin "attr_table_1.bin"
palette:
.incbin "palette_0.bin"
.incbin "palette_1.bin"
.incbin "palette_2.bin"
.incbin "palette_3.bin"
.bank 2
.org $0000
.incbin "pattern_0.bin"
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