From 45fd0ca73ec84a9b605f918a7b1b3497d2a25b33 Mon Sep 17 00:00:00 2001
From: Ian C <ianc@noddybox.co.uk>
Date: Fri, 20 May 2016 15:23:00 +0100
Subject: First pass at NES ROM support.

---
 src/example/Makefile |  5 +++-
 src/example/nes.asm  | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+), 1 deletion(-)
 create mode 100644 src/example/nes.asm

(limited to 'src/example')

diff --git a/src/example/Makefile b/src/example/Makefile
index 3c57e50..e92b2ec 100644
--- a/src/example/Makefile
+++ b/src/example/Makefile
@@ -20,7 +20,7 @@
 # Makefile for examples
 #
 
-ALL	= spectrum.tap c64.t64 zx81.p gb.gb vcs.bin snes.sfc
+ALL	= spectrum.tap c64.t64 zx81.p gb.gb vcs.bin snes.sfc nes.nes
 CASM	= ../casm
 
 all: $(ALL) $(CASM)
@@ -48,5 +48,8 @@ vcs.bin: vcs.asm $(CASM)
 snes.sfc: snes.asm $(CASM)
 	$(CASM) snes.asm
 
+nes.nes: nes.asm $(CASM)
+	$(CASM) nes.asm
+
 clean:
 	rm -f $(ALL)
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
-- 
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