Add the early "DMG0" boot ROM.

2 files changed, 165 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index baad5a0..52a237d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 .SUFFIXES: .s .o .bin
 
-all: dmg.bin mgb.bin
+all: dmg0.bin dmg.bin mgb.bin
 
 .s.o:
 	rgbasm -o $@ $<
diff --git a/dmg0.s b/dmg0.s
new file mode 100644
index 0000000..47c8a2e
--- /dev/null
+++ b/dmg0.s
@@ -0,0 +1,164 @@
+SECTION "blah",rom0
+	; set up stack
+	ld sp,$fffe
+
+	; clear vram ($8000–9fff)
+	xor a
+	ld hl,$9fff
+vloop:
+	ld [hld],a
+	bit 7,h
+	jr nz,vloop
+
+	; set up audio
+	ld hl,$ff26
+	ld c,$11
+	ld a,$80
+	ld [hld],a
+	ld [$ff00+c],a
+	inc c
+	ld a,$f3
+	ld [$ff00+c],a
+	ld [hld],a
+	ld a,$77
+	ld [hl],a
+
+	; set background palette
+	ld a,$fc
+	ld [$ff47],a
+
+	; convert and load logo data from cart into vram
+	ld hl,$0104 ; cart logo
+	push hl
+	ld de,logo
+
+lastbranch:
+	ld a,[de]
+	inc de
+	cp [hl] ; compare cart logo to bootrom logo
+	jr nz,loop98
+	inc hl
+	ld a,l
+	cp $34
+	jr nz,lastbranch
+
+	ld b,$19
+	ld a,b
+cloop:
+	add [hl]
+	inc hl
+	dec b
+	jr nz,cloop
+	add [hl]
+
+	jr nz,loop98
+	pop de
+	ld hl,$8010
+loopf3:
+	ld a,[de]
+	call funca9
+	call funcaa
+	inc de
+	ld a,e
+	cp $34
+	jr nz,loopf3
+	ld a,$18
+	ld hl,$992f
+loopf1:
+	ld c,$c
+loop56:
+	ld [hld],a
+	dec a
+	jr z,loop09
+	dec c
+	jr nz,loop56
+	ld de,$ffec
+	add hl,de
+	jr loopf1
+loop09:
+	ld h,a
+	ld a,$64
+	ld d,a
+	ld [$ff42],a
+	ld a,$91
+	ld [$ff40],a
+	inc b
+loop6e:
+	ld e,2
+	call funcbc
+	ld c,$13
+	inc h
+	ld a,h
+	ld e,$83
+	cp $62
+	jr z,loop83
+	ld e,$c1
+	cp $64
+	jr nz,loop89
+loop83:
+	ld a,e
+	ld [$ff00+c],a
+	inc c
+	ld a,$87
+	ld [$ff00+c],a
+loop89:
+	ld a,[$ff42]
+	sub b
+	ld [$ff42],a
+	dec d
+	jr nz,loop6e
+	dec b
+	jr nz,end
+	ld d,$20
+	jr loop6e
+loop98:
+	ld a,$91
+	ld [$ff40],a
+loop9c:
+	ld e,$14
+	call funcbc
+	ld a,[$ff47]
+	xor $ff
+	ld [$ff47],a
+	jr loop9c
+funca9:
+	ld c,a
+funcaa:
+	ld b,4
+
+dloop:
+	push bc
+	rl c
+	rla
+	pop bc
+	rl c
+	rla
+	dec b
+	jr nz,dloop
+	ld [hli],a
+	inc hl
+	ld [hli],a
+	inc hl
+	ret
+funcbc:
+	ld c,$c
+loopbe:
+	ld a,[$ff44]
+	cp $90
+	jr nz,loopbe
+	dec c
+	jr nz,loopbe
+	dec e
+	jr nz,funcbc
+	ret
+
+logo:
+	db $ce,$ed,$66,$66,$cc,$0d,$00,$0b,$03,$73,$00,$83,$00,$0c,$00,$0d
+	db $00,$08,$11,$1f,$88,$89,$00,$0e,$dc,$cc,$6e,$e6,$dd,$dd,$d9,$99
+	db $bb,$bb,$67,$63,$6e,$0e,$ec,$cc,$dd,$dc,$99,$9f,$bb,$b9,$33,$3e
+
+	db $ff,$ff
+
+end:
+	inc a
+	ld [$ff50],a ; turn off bootrom