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Atari coding BBS
| Timer-B at several lines? |
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Posted by: PeyloW
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Apr,23.2015-17:13
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I am creating auto generated code for timer-b interrupts, for setting colors and new screen address for screen splits. Obviously I want to avoid the timer firing every line, so I use the counting mode and the timer-b counter in $fa1b.w.
The counter set in the vbl is respected, but from there on the new counters set in the timer-b interrupts are used "one to late". I guess a solution would be to always generate a dummy interrupt doing nothing but setting the counter, and have all the counter updates adjusted for "one too early".
Or is there a proper solution?
My generated code looks something like this:
vbl:
addq.w #1,vblcount
move.w #$000,$fffff8240.w
clr.b $fffffa1b.w
move.b #32,$fffffa21.w
move.b #8,$fffffa1b.w
move.l #timer_b1,$120.w
save_vbl:
jmp $12345678
timer_b1:
move.w #$700,$fffff8240.w
move.l #timer_b2,$120.w
move.b #16,$fffffa21.w
rte
timer_b2:
move.w #$070,$fffff8240.w
move.l #timer_b3,$120.w
move.b #8,$fffffa21.w
rte
timer_b3:
move.w #$007,$fffff8240.w
move.l #timer_b4,$120.w
move.b #4,$fffffa21.w
rte
timer_b4:
move.w #$000,$fffff8240.w
clr.b $fffffa1b.w
rte
I expect black until line 32. Then red for 16 lines, green for 8 lines, and finally blue for 4 lines.
But what I get is black until line 32. Then red for 32 lines, green for 16 lines, and blue for 8 lines.
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