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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
.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 #4
.loop:
lda [COPY_SOURCE_ADDR], y
sta PPUDATA
iny
dex
bne .loop
; loading blank nametable
clear_nametable:
lda PPUSTATUS
lda #$20
sta PPUADDR
lda #$00
sta PPUADDR
ldy #0
ldx #0
lda #$20
.loop:
cpy #$C0
bne .noat
cpx #$03
bne .noat
lda #$00
.noat:
sta PPUDATA
iny
bne .loop
inx
cpx #$04
bne .loop
.end:
; write HELLO WORLD
load_text:
lda PPUSTATUS
lda #$20
sta PPUADDR
lda #$41
sta PPUADDR
lda #LOW(.hello_world)
sta COPY_SOURCE_ADDR
lda #HIGH(.hello_world)
sta COPY_SOURCE_ADDR+1
ldy #0
.loop:
lda [COPY_SOURCE_ADDR], y
beq .end
sta PPUDATA
iny
jmp .loop
.hello_world:
.db "HELLO WORLD!", 0
.end:
; enable PPU
jsr waitblank
lda #%00001010
sta PPUMASK
lda #%00000000
sta PPUCTRL
main_loop:
jsr waitblank
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"
.bank 2
.org $0200
.incbin "pattern_0.bin"
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