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Post by VDC 8x2 on Jun 5, 2014 4:17:13 GMT
I know it was answered before but for the sake of new people.
How did risen from oblivion do its raster effects?
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Post by VDC 8x2 on Jun 19, 2014 7:45:04 GMT
Some code I pulled out of risen from oblivion.
*=$fe11
start sei
lda #$20 ;wait for vblank
and $d600
beq *-5
lda #>fe31 ;irq vector
sta $fffe
lda #>$fe31
sta $ffff
lda #$20 ;wait for screen
and $d600
bne *-5
lda #$19 ;set cia1 clock
sta $dc0e
cli
rts
irqfe31 pha
lda $dc0d ;clear irq source
lda #$20
and $d600
bne *-5 ;wait for screen
lda #$19
sta $dc0e ;set cia1 clock
txa
pha ;push x on the stack
tya
pha ;push y on the stack
jsr $e003
pla
tay ;pull y from the stack
pla
tax ;pull x from the stack
pla ;pull a from the stack
rti ;return from the irq
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Post by hydrophilic on Jun 19, 2014 10:53:54 GMT
Thanks for taking the time... I did notice an error in that:
lda #>fe31 ;irq vector
sta $fffe
lda #>$fe31
sta $ffff
which should instead read:
lda #<fe31 ;irq vector
sta $fffe
lda #>$fe31
sta $ffff
Notice the low-byte and high-byte operators. That is a very trivial detail to me... more important is this:
lda #$20 ;wait for screen
and $d600
bne *-5
Now that seems like the crap you would see by a lame programmer; I think most of us would agree RFOB is pretty cool, so this really surprises me! I mean, wouldn't this be better?
lda #$20
bit $d600 ;wait for screen
bne *-3...
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Post by VDC 8x2 on Jun 19, 2014 20:25:05 GMT
It would not be better because the code is waiting for the vblank bit? Am I wrong?
does bit change the A reg?
yeah the bitwise stuff was a typo on my part.
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Post by VDC 8x2 on Jun 19, 2014 20:32:36 GMT
Never mind, I see what you mean. bit does the and thing
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Post by VDC 8x2 on Jun 19, 2014 20:34:36 GMT
Looking into its code to look for ideas on doing a split screen with graphics and text on vdc.
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