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2015-02-12 17:04

Flavioweb

Registered: Nov 2011
Posts: 463

Facts about CIA and... question.

Obviously, correct me if i'm wrong.
- I know that CIA's counters $DC04..07, $DD04..07 never reach the value $00 during countdown, but $01 is repeated twice (EDIT: not $01, but the reset value is repeated twice).
- After that, i know that CIA's TOD alarm 1/10 seconds register, can't be set at value $00 otherwise the alarm does not work.
- Then i know that, if ICR is readed 1 or 2 cycles just before an IRQ generated by Timer B occur, then IRQ don't occur at all..
But... what are "the differences" between CIA revisions?
Not all of these bugs occur on all revisions or there are other differences?

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2015-03-05 13:24

enthusi

Registered: May 2004
Posts: 677

I remember this being a pain for Hawkeye2 at X-Party ;-)
(there still is some bug-fixed-smile pic of yours somewhere)

2015-03-05 18:33

White Flame

Registered: Sep 2002
Posts: 136

That pain was that the demo machine ended up having 1 cycle of jitter more in its initial interrupt than I supported, or had seen before in VICE. It was a pain to figure out what was going on, but fortunately relatively easy to fix.

Inside my interrupt handler, I used the jitter value as an offset to INC some unused area and was able to build up a histogram of actual jitter observed. Using timer interrupts for cycle-accurate effects is nice because you can directly read the jitter amount from the CIA timer registers.

If I remember correctly, it's not that it had a 1-cycle phase offset to what I was expecting, but had a legitimately larger range of jitter possibilities for whatever reason.

2015-03-09 10:02

enthusi

Registered: May 2004
Posts: 677

That very moment: