8bitforever
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Registered: Oct 2009
Posts: 48 |
Howto flickerfree and moving rasterbar ?
<Post edited by moderator on 20/10-2009 01:24>
Making a perfect stable, flickerfree and moving rasterbar is harder than I thought.
Why and which changes are needed to the code below to fulfill my dream about the flickerfree rasterbar?
The code is based on http://www.ffd2.com/fridge/vic/stableraster.txt.
Acme code ready to compile:
!to "doubleirqrasterbar1.prg",cbm
*= $0800
!byte $00,$0c,$08,$0a,$00,$9e,$33,$32,$37,$36,$38,$00,$00,$00,$00
raspos = $00
maxpos = $7c
*= $8000 ;Assemble to $8000
cld ;Clear Decimal Mode
sei ;Disable IRQ's
lda #$1f ;Disable CIA IRQ's
sta $dc0d
sta $dd0d
; lda #<nmi ;Install NMI into
; ldx #>nmi ;Hardware NMI and
; sta $fffa ;RESET Vectors
; sta $fffc
; stx $fffb
; stx $fffd
lda #<irq1 ;Install RASTER IRQ
ldx #>irq1 ;into Hardware
sta $0314 ;Interrupt Vector
stx $0315
; lda #$35 ;Set MMU to RAM at
; ldx #$ff ;$a000-$bfff and
; sta $01 ;$e000-$ffff
; txs ;Clear the STACK
lda #$01 ;Enable RASTER IRQ
ldx #$1b ;High bit of RASTER
ldy #$34 ;compare register
sta $d01a ;and RASTER IRQ to
stx $d011 ;line $34
sty $d012
;NOTE double IRQ
;cannot be on or
;around a BAD LINE!
;(Fast Line)
lda #$0e ;Set Background
ldx #$06 ;and Border colors
ldy #$00 ;to default and
sta $d020 ;turn off sprites
stx $d021
sty $d015
jsr clrscreen
jsr clrcolor
; jsr printtext
asl $d019 ;Ack any previous
lda $dc0d ;IRQ's
lda $dd0d
cli ;Renable IRQ's
jmp * ;Endless Loop
irq1
sta reseta1 ;Preserve A,X and Y
stx resetx1 ;Registers
sty resety1 ;VIA self modifying
;code
;(Faster than the
;STACK is!)
lda #<irq2 ;Set IRQ Vector
ldx #>irq2 ;to point to the
ldy #$35 ;next part of the
sta $0314 ;Stable IRQ
stx $0315 ;ON NEXT LINE!
sty $d012
asl $d019 ;Ack RASTER IRQ
tsx ;We want the IRQ
cli ;To return to our
nop ;endless loop
nop ;NOT THE END OF
nop ;THIS IRQ!
nop
nop ;Execute nop's
nop ;until next RASTER
nop ;IRQ Triggers
nop
nop ;2 cycles per
nop ;instruction so
nop ;we will be within
nop ;1 cycle of RASTER
nop ;Register change
; nop ;<--- remove 1 NOP for PAL
irq2
txs ;Restore STACK
;Pointer
ldx #$08 ;Wait exactly 1
dex ;lines worth of
bne *-1 ;cycles for compare
bit $ea ;Minus compare
nop ;cycles
; nop ;<--- remove 1 NOP for PAL
lda #$35 ;RASTER change yet?
cmp $d012
beq start ;If no waste 1 more
;cycle
start
ldx raspos
cpx #maxpos
beq setrastup
inx
stx raspos
cpx #maxpos
bne rasterbarctrl
setrastup
ldx #$00
stx raspos ;Reset raster positon to
;zero if maximum has been reached.
rasterbarctrl
ldx raspos
ldy rastmov,x ;Wait for rasterline $3D-$96 at $D012
wait cpy $d012
bne wait
;rasterbar
ldx #$00
copy11 ldy rastime,x
dey
bne *-1
lda coloursr,x
sta $d020
sta $d021
inx
cpx #$10
bne copy11
lda #<irq3 ;Set IRQ to point
ldx #>irq3 ;to subsequent IRQ
ldy #$b8 ;at line $68
sta $0314
stx $0315
sty $d012
asl $d019 ;Ack RASTER IRQ
lda #$00 ;Reload A,X,and Y
reseta1 = *-1 ;registers
ldx #$00
resetx1 = *-1
ldy #$00
resety1 = *-1
; rti ;Return from IRQ
jmp $ea31
irq3
sta reseta2 ;Preserve A,X,and Y
stx resetx2 ;Registers
sty resety2
ldx #$0a ;Waste some more
dex ;time so effect
bne *-1 ;can be seen
nop
; lda #$0e ;More colors
; ldx #$06
; nop:nop
; sta $d021 ;Cool! subsequent
; stx $d021 ;IRQ's are also
;stable :-)
;Unless you are
;running realtime
;code :-)
ldy #$18 ;Waste time so this
dey ;IRQ does not try
bne *-1 ;to reoccur on the
;same line!
lda #<irq1 ;Reset Vectors to
ldx #>irq1 ;first IRQ again
ldy #$34 ;at line $34
sta $0314
stx $0315
sty $d012
asl $d019 ;Ack RASTER IRQ
lda #$00 ;Reload A,X,and Y
reseta2 = *-1 ;registers
ldx #$00
resetx2 = *-1
ldy #$00
resety2 = *-1
; rti ;Return from IRQ
jmp $ea81
;Pound RESTORE to
;get back to Turbo
nmi
asl $d019 ;Ack all IRQ's
lda $dc0d
lda $dd0d
lda #$81 ;reset CIA 1 IRQ
ldx #$00 ;remove raster IRQ
ldy #$37 ;reset MMU to roms
sta $dc0d
stx $d01a
sty $01
ldx #$ff ;clear the stack
txs
cli ;reenable IRQ's
jmp $9000 ;back to Turbo
clrscreen
lda #$20 ;Clear the screen
ldx #$00
clrscr sta $0400,x
sta $0500,x
sta $0600,x
sta $0700,x
dex
bne clrscr
rts
clrcolor
lda #$03 ;Clear color memory
ldx #$00
clrcol sta $d800,x
sta $d900,x
sta $da00,x
sta $db00,x
dex
bne clrcol
rts
printtext
lda #$16 ;C-set = lower case
sta $d018
ldx #$00
moretext lda text1,x
bpl lower ;upper case ?
eor #$80 ;yes
bne lower+2
lower and #$3f ;lower case
sta $0450,x
inx
cpx #$78
bne moretext
exit rts
text1
!scr "Stable Raster IRQ sourc"
!scr "e (PAL/NTSC) "
!scr "All Code by Fungus 1996"
!scr " "
!scr "Feel free to use and mo"
!scr "dify this code :)"
;------------------------------------------------------------------------------- -
;raster data
;------------------------------------------------------------------------------- -
rastime
!byte $08,$08,$08,$08,$08,$08,$08,$01
!byte $08,$08,$08,$08,$08,$08,$08,$01
coloursr
!byte $0b,$0b,$0c,$0c,$0f,$0f,$0d,$0d
!byte $0d,$0f,$0f,$0c,$0c,$0b,$0b,$00
rastmov
!byte $3D,$3D,$3E,$3E,$3F,$3F,$40,$40,$41,$42,$43,$44,$45,$46,$47,$48
!byte $49,$4A,$4C,$4E,$50,$52,$54,$56,$58,$5A,$5C,$5E,$60,$62,$64,$66
!byte $68,$6A,$6C,$6E,$70,$72,$74,$76,$78,$7A,$7C,$7E,$80,$82,$84,$86
!byte $88,$8A,$8C,$8E,$8F,$90,$91,$92,$93,$94,$94,$95,$95,$96,$96,$95
!byte $95,$94,$94,$93,$93,$92,$91,$90,$8F,$8E,$8D,$8D,$8B,$89,$87,$85
!byte $83,$81,$7F,$7D,$7B,$79,$77,$75,$73,$71,$6F,$6D,$6B,$69,$67,$65
!byte $63,$61,$5F,$5D,$5B,$59,$57,$55,$53,$51,$4F,$4D,$4B,$49,$48,$47
!byte $46,$45,$44,$43,$42,$41,$40,$40,$3F,$3F,$3E,$3E
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