Gameboy Development Forum

thrawn235 · 2018-03-26 11:41:41

Hello all, i have recently started to mess with GB programming. I've read quite a bit of technical information and thought i would be ready to finally code something.

I came up with this little hello world program:

Code:

include "inc/gbhw.inc"
include "inc/ibmpc1.inc"

SECTION "Vblank", ROM0[$0040]
ret
SECTION "LCDC", ROM0[$0048]
ret
SECTION "TimerOverflow", ROM0[$0050]
ret
SECTION "Serial", ROM0[$0058]
ret
SECTION "Joypad", ROM0[$0060]
ret

SECTION "Header", ROM0[$0100]
nop
jp Main

Section "Logo", ROM0[$0104]
DB $CE, $ED, $66, $66, $CC, $0D, $00, $0B
DB $03, $73, $00, $83, $00, $0C, $00, $0D
DB $00, $08, $11, $1F, $88, $89, $00, $0E
DB $DC, $CC, $6E, $E6, $DD, $DD, $D9, $99
DB $BB, $BB, $67, $63, $6E, $0E, $EC, $CC
DB $DD, $DC, $99, $9F, $BB, $B9, $33, $3E

Section "Title", ROM0[$0134]
db "title"

Section "GBCComp", ROM0[$0143]
DB $C0

Section "Data", ROM0
HELLO_TILES::
DB $00,$00,$00,$00,$00,$00,$00,$00
DB $00,$00,$00,$00,$00,$00,$00,$00
DB $C6,$C6,$C6,$C6,$C6,$C6,$FE,$FE
DB $FE,$FE,$C6,$C6,$C6,$C6,$C6,$C6
DB $FE,$FE,$FE,$FE,$80,$80,$F8,$F8
DB $F8,$F8,$80,$80,$FE,$FE,$FE,$FE
DB $C0,$C0,$C0,$C0,$C0,$C0,$C0,$C0
DB $C0,$C0,$C0,$C0,$FE,$FE,$FE,$FE
DB $7C,$7C,$FE,$FE,$C6,$C6,$C6,$C6
DB $C6,$C6,$C6,$C6,$FE,$FE,$7C,$7C
DB $C6,$C6,$C6,$C6,$C6,$C6,$C6,$C6
DB $D6,$D6,$D6,$D6,$FE,$FE,$6C,$6C
DB $FC,$FC,$FE,$FE,$C6,$C6,$FC,$FC
DB $FC,$FC,$C6,$C6,$C6,$C6,$C6,$C6
DB $FC,$FC,$FE,$FE,$C6,$C6,$C6,$C6
DB $C6,$C6,$C6,$C6,$FE,$FE,$FC,$FC
DB $6C,$6C,$6C,$6C,$6C,$6C,$6C,$6C
DB $6C,$6C,$6C,$6C,$00,$00,$6C,$6C

HELLO_MAP::
DB $01,$02,$03,$03,$04,$00,$05,$04,$06,$03,$07,$08

SECTION "main", ROM0[$0150]

WaitVBlank:
ld a, [$ff44]
cp 144
jp c, WaitVBlank
ret

LoadTiles:
ld hl, HELLO_TILES
ld de, _VRAM
ld bc, 9*16
LoadTilesLoop:
call WaitVBlank
ld a, [hl]
ld [de], a
inc de
inc hl
dec bc
ld a, b
or c
jr nz, LoadTilesLoop
ret

LoadMap:
ld hl, HELLO_MAP
ld de, $9800
ld c, 12
LoadMapLoop:
call WaitVBlank
ld a, [hl]
ld [de], a
inc de
inc hl
dec bc
ld a, b
or c
jr nz,LoadMapLoop
ret

Main:
    ld sp, $ffff
    call LoadTiles
    call LoadMap
.Wait:
        halt
        nop
        jr .Wait

The "LoadTiles" function seems to work fine, i can verify with bgb that the tiles end up in vram.
But every time "loadMap" writes a value to $9800 it simultaneously deletes a tile from the beginning of Vram ($8000)
It writes the value in the tilemap, but in never displays anything because by then, all the actual tiles are deleted ?

I just dont understand whats going on here.

Am i missing something ?

Last edited by thrawn235 (2018-03-26 11:43:40)

tbsp · 2018-03-26 12:56:52

What looks like 'deleting' the tiles is most likely using them, but with no palette assigned. When tiles are used bgb changes their coloring to match the palette in use (or something like that).

Code:

    ld      a,%11100100 ; Set Palettes
    ldh     [rBGP],a
    ldh     [rOBP0],a
    ldh     [rOBP1],a

Gameboy Development Forum

#1 2018-03-26 11:41:41

writing the tilemap deletes VRAM ?

Code:

#2 2018-03-26 12:56:52

Re: writing the tilemap deletes VRAM ?

Code:

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