1 files changed, 196 insertions, 0 deletions
diff --git a/sgb2.s b/sgb2.s
new file mode 100644
index 0000000..a8b5f22
--- /dev/null
+++ b/sgb2.s
@@ -0,0 +1,196 @@
+SECTION "main",rom0
+	; set up stack
+	ld sp,$fffe
+
+	ld a,$30
+	ld [$ff00],a
+
+	; 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 [$ff47],a
+	ld hl,$c05f
+	ld c,8
+	xor a
+loop2b:
+	ld [hld],a
+	dec c
+	jr nz,loop2b
+
+	ld de,$014f
+	ld a,$fb
+	ld c,6
+loop36:
+	push af
+	ld b,0
+loop39:
+	ld a,[de]
+	dec de
+	ld [hld],a
+	add b
+	ld b,a
+	dec c
+	jr nz,loop39
+
+	ld [hld],a
+	pop af
+	ld [hld],a
+	ld c,$e
+	sub 2
+	cp $ef
+	jr nz,loop36
+
+	; convert and load logo data from cart into vram
+	ld de,$0104
+	ld hl,$8010
+lloop:
+	ld a,[de]
+	call Graphics
+	call Graphics2
+	inc de
+	ld a,e
+	cp $34
+	jr nz,lloop
+
+	; load 8 additional bytes into vram
+	ld de,moredata
+	ld b,moredata_ - moredata
+eloop:
+	ld a,[de]
+	inc de
+	ld [hli],a
+	inc hl
+	dec b
+	jr nz,eloop
+
+	; set background tilemap
+	ld a,$19
+	ld [$9910],a
+	ld hl,$992f
+oloop:
+	ld c,$0c
+iloop:
+	dec a
+	jr z,scroll
+	ld [hld],a
+	dec c
+	jr nz,iloop
+	ld l,$f
+	jr oloop
+scroll:
+	; turn on lcd (showing background)
+	ld a,$91
+	ld [$ff40],a
+	ld hl,$c000
+	ld c,0
+loop89:
+	ld a,0
+	ld [$ff00+c],a
+	ld a,$30
+	ld [$ff00+c],a
+	ld b,$10
+loop91:
+	ld e,8
+	ld a,[hli]
+	ld d,a
+loop95:
+	bit 0,d
+	ld a,$10
+	jr nz,loop9d
+	ld a,$20
+loop9d:
+	ld [$ff00+c],a
+	ld a,$30
+	ld [$ff00+c],a
+	rr d
+	dec e
+	jr nz,loop95
+	dec b
+	jr nz,loop91
+	ld a,$20
+	ld [$ff00+c],a
+	ld a,$30
+	ld [$ff00+c],a
+	call funcc2
+	ld a,l
+	cp $60
+	jr nz,loop89
+	ld c,$13
+	ld a,$c1
+	ld [$ff00+c],a
+	inc c
+	ld a,7
+	ld [$ff00+c],a
+	jr end
+funcc2:
+	ld d,4
+loopc4:
+	ld a,[$ff44]
+	cp $90
+	jr nz,loopc4
+	ld e,0
+loopcc:
+	dec e
+	jr nz,loopcc
+	dec d
+	jr nz,loopc4
+	ret
+Graphics:
+	ld c,a
+Graphics2:
+	ld b,4
+loopd6:
+	push bc
+	rl c
+	rla
+	pop bc
+	rl c
+	rla
+	dec b
+	jr nz,loopd6
+	ld [hli],a
+	inc hl
+	ld [hli],a
+	inc hl
+	ret
+
+moredata:
+	db $3c,$42,$b9,$a5,$b9,$a5,$42,$3c
+moredata_:
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+end:
+	ld a,-1
+	ld [$ff50],a ; turn off bootrom