cc65/libsrc/nes/ppu.s

;
; Written by Groepaz/Hitmen <groepaz@gmx.net>
; Cleanup by Ullrich von Bassewitz <uz@cc65.org>
;

	.export ppuinit
	.export paletteinit, paldata

	.include "nes.inc"

;+---------+----------------------------------------------------------+
;|  $2000  | PPU Control Register #1 (W)			      |
;|	   |							      |
;|	   |	D7: Execute NMI on VBlank			      |
;|	   |	       0 = Disabled				      |
;|	   |	       1 = Enabled				      |
;|	   |	D6: PPU Master/Slave Selection --+		      |
;|	   |	       0 = Master		 +-- UNUSED	      |
;|	   |	       1 = Slave	       --+		      |
;|	   |	D5: Sprite Size					      |
;|	   |	       0 = 8x8					      |
;|	   |	       1 = 8x16					      |
;|	   |	D4: Background Pattern Table Address		      |
;|	   |	       0 = $0000 (VRAM)				      |
;|	   |	       1 = $1000 (VRAM)				      |
;|	   |	D3: Sprite Pattern Table Address		      |
;|	   |	       0 = $0000 (VRAM)				      |
;|	   |	       1 = $1000 (VRAM)				      |
;|	   |	D2: PPU Address Increment			      |
;|	   |	       0 = Increment by 1			      |
;|	   |	       1 = Increment by 32			      |
;|	   | D1-D0: Name Table Address				      |
;|	   |	     00 = $2000 (VRAM)				      |
;|	   |	     01 = $2400 (VRAM)				      |
;|	   |	     10 = $2800 (VRAM)				      |
;|	   |	     11 = $2C00 (VRAM)				      |
;+---------+----------------------------------------------------------+
;+---------+----------------------------------------------------------+
;|  $2001  | PPU Control Register #2 (W)			      |
;|	   |							      |
;|	   | D7-D5: Full Background Colour (when D0 == 1)	      |
;|	   |	     000 = None	 +------------+			      |
;|	   |	     001 = Green	      | NOTE: Do not use more |
;|	   |	     010 = Blue		      |	      than one type   |
;|	   |	     100 = Red	 +------------+			      |
;|	   | D7-D5: Colour Intensity (when D0 == 0)		      |
;|	   |	     000 = None		   +--+			      |
;|	   |	     001 = Intensify green    | NOTE: Do not use more |
;|	   |	     010 = Intensify blue     |	      than one type   |
;|	   |	     100 = Intensify red   +--+			      |
;|	   |	D4: Sprite Visibility				      |
;|	   |	       0 = Sprites not displayed		      |
;|	   |	       1 = Sprites visible			      |
;|	   |	D3: Background Visibility			      |
;|	   |	       0 = Background not displayed		      |
;|	   |	       1 = Background visible			      |
;|	   |	D2: Sprite Clipping				      |
;|	   |	       0 = Sprites invisible in left 8-pixel column   |
;|	   |	       1 = No clipping				      |
;|	   |	D1: Background Clipping				      |
;|	   |	       0 = BG invisible in left 8-pixel column	      |
;|	   |	       1 = No clipping				      |
;|	   |	D0: Display Type				      |
;|	   |	       0 = Colour display			      |
;|	   |	       1 = Monochrome display			      |
;+---------+----------------------------------------------------------+


;-----------------------------------------------------------------------------

.proc	ppuinit

	lda #%10101000
	sta PPU_CTRL1

	lda	#%00011110
	sta	PPU_CTRL2

; Wait for vblank

@wait:	lda	PPU_STATUS
	bpl	@wait

; reset scrolling

	lda	#0
	sta	PPU_VRAM_ADDR1
	sta	PPU_VRAM_ADDR1

; Make all sprites invisible

	lda	#$00
	ldy	#$f0
	sta	PPU_SPR_ADDR
	ldx	#$40
@loop:	sty	PPU_SPR_IO
	sta	PPU_SPR_IO
	sta	PPU_SPR_IO
	sty	PPU_SPR_IO
	dex
	bne	@loop

	rts

.endproc


;-----------------------------------------------------------------------------

.proc	paletteinit

; Wait for v-blank
@wait:	lda	PPU_STATUS
	bpl	@wait

	lda	#$3F
	sta	PPU_VRAM_ADDR2
	lda	#$00
	sta	PPU_VRAM_ADDR2

	ldx	#0
@loop:	lda	paldata,x
	sta	PPU_VRAM_IO
	inx
	cpx	#(16*2)
	bne	@loop

	rts
		     
.endproc

;-----------------------------------------------------------------------------

.rodata

paldata:
	.repeat 2
	.byte	$0f	; 0 black
	.byte	$14	; 4 violett
	.byte	$3b	; 3 cyan
	.byte	$3d	; 1 white

	.byte	$38	; 7 yellow
	.byte	$2d	; b dark grey
	.byte	$22	; e light blue
	.byte	$04	; 2 red

	.byte	$18	; 8 orange
	.byte	$08	; 9 brown
	.byte	$35	; a light red
	.byte	$01	; 6 blue

	.byte	$10	; c middle grey
	.byte	$2b	; d light green
	.byte	$3d	; f light gray
	.byte	$1a	; 5 green
	.endrepeat