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|
processor 6502
option output-file,"nes.nes"
option output-format,nes
option nes-vector,reset,start
option nes-vector,nmi,nmi
option nes-vector,brk,nmi
start: org $c000
;
; Code taken from NES example
;
sei ; disable IRQs
cld ; disable decimal mode
ldx #$40
stx $4017 ; dsiable APU frame IRQ
ldx #$ff ; Set up stack
txs ; .
inx ; now X = 0
stx $2000 ; disable NMI
stx $2001 ; disable rendering
stx $4010 ; disable DMC IRQs
;; first wait for vblank to make sure PPU is ready
vblankwait1:
bit $2002
bpl vblankwait1
clear_memory:
lda #$00
sta $0000, x
sta $0100, x
sta $0200, x
sta $0300, x
sta $0400, x
sta $0500, x
sta $0600, x
sta $0700, x
inx
bne clear_memory
;; second wait for vblank, PPU is ready after this
vblankwait2:
bit $2002
bpl vblankwait2
clear_palette:
;; Need clear both palettes to $00. Needed for Nestopia. Not
;; needed for FCEU* as they're already $00 on powerup.
lda $2002 ; Read PPU status to reset PPU address
lda #$3f ; Set PPU address to BG palette RAM ($3F00)
sta $2006
lda #$00
sta $2006
ldx #$20 ; Loop $20 times (up to $3F20)
lda #$00 ; Set each entry to $00
.loop
sta $2007
dex
bne loop
lda #%10000000 ; intensify blues
sta $2001
forever:
jmp forever
nmi:
rti
;
; Dummy VROM
;
org 0
bank 1
db 0
|
