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sms/vdp: improve comments

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This commit is contained in:
Virgil Dupras 2020-01-08 18:38:55 -05:00
parent 927d5f2392
commit d70c6d3b5f
1 changed files with 19 additions and 10 deletions
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29
kernel/sms/vdp.asm
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@ -38,6 +38,7 @@ vdpInit:
ld c, VDP_CTLPORT
otir
; Blank VRAM
xor a
out (VDP_CTLPORT), a
ld a, 0x40
@ -51,15 +52,17 @@ vdpInit:
or c
jr nz, .loop1
; Set palettes
xor a
out (VDP_CTLPORT), a
ld a, 0xc0
out (VDP_CTLPORT), a
ld hl, vdpPaletteData
ld b, vdpPaletteDataEnd-vdpPaletteData
ld c, VDP_DATAPORT
otir
xor a ; palette 0: black
out (VDP_DATAPORT), a
ld a, 0x3f ; palette 1: white
out (VDP_DATAPORT), a
; Define tiles
xor a
out (VDP_CTLPORT), a
ld a, 0x40
@ -97,6 +100,7 @@ vdpInit:
dec c
jr nz, .loop2
; Bit 7 = ?, Bit 6 = display enabled
ld a, 0b11000000
out (VDP_CTLPORT), a
ld a, 0x81
@ -129,7 +133,7 @@ vdpSpitC:
; two bits
out (VDP_CTLPORT), a
ld a, b ; 3 low bits set
or 0x78
or 0x78 ; 01 header + 0x3800
out (VDP_CTLPORT), a
pop bc
@ -279,11 +283,16 @@ vdpConv:
ld a, 0x5e
ret
vdpPaletteData:
.db 0x00,0x3f
vdpPaletteDataEnd:
; VDP initialisation data
vdpInitData:
.db 0x04,0x80,0x00,0x81,0xff,0x82,0xff,0x85,0xff,0x86,0xff,0x87,0x00,0x88,0x00,0x89,0xff,0x8a
; 0x8x == set register X
.db 0b00000100, 0x80 ; Bit 2: Select mode 4
.db 0b00000000, 0x81
.db 0b11111111, 0x82 ; Name table: 0x3800
.db 0b11111111, 0x85 ; Sprite table: 0x3f00
.db 0b11111111, 0x86 ; sprite use tiles from 0x2000
.db 0b11111111, 0x87 ; Border uses palette 0xf
.db 0b00000000, 0x88 ; BG X scroll
.db 0b00000000, 0x89 ; BG Y scroll
.db 0b11111111, 0x8a ; Line counter (why have this?)
vdpInitDataEnd: