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Diffstat (limited to 'src/example/nes.asm')
| -rw-r--r-- | src/example/nes.asm | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/src/example/nes.asm b/src/example/nes.asm new file mode 100644 index 0000000..c10ca66 --- /dev/null +++ b/src/example/nes.asm @@ -0,0 +1,82 @@ + 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 #%01000000 ; intensify blues + sta $2001 + +forever: + jmp forever + +nmi: + rti + + +; +; Dummy VROM +; + org 0 + bank 1 + + db 0 |