[Coco] CoCo's TIMER and 60hz

Allen Huffman alsplace at pobox.com
Thu May 30 10:17:42 EDT 2019

On May 30, 2019, at 8:58 AM, L. Curtis Boyle <curtisboyle at sasktel.net> wrote:
> The HALT based floppy driver definitely caused missed VSYNCS, so if it is emulating that hardware, that would cause problems keeping time accurate (it certainly did on a real Coco).

This would be expected.

I ran Disto Super Controller 2 on my floppy OS-9 system, no halt, and later hard drives, also no halt. CoCoSDC seems to halt (I lose characters while typing during disk access).

But sitting in BASIC with nothing going on should be pretty accurate, except for the occasional missed count for break detection that Art mentioned.

There are two Matchbox issues I was trying to understand, and I think both have been cleared up. One is a slightly different timing rate, and the other is a different rate based on the new graphics modes. I expect both can be tweaked to get us closer to CoCo time.

I don’t think we expect something written to run in an all new graphics mode to behave exactly like a real CoCo because that CoCo didn’t have the mode :) But, fixing the part that drives the OS-9 clock and causes it to get wildly off is needed, and Roger is on that.

My original question was mostly about if what I was seeing was Matchbox related, or if real CoCos drifted the same way. In BASIC, I saw a two second drift within the first 8 minutes. Not huge.

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