First pass at NES ROM support.

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