[Coco] CoCo's TIMER and 60hz

[Allen Huffman]

> On May 29, 2019, at 1:20 PM, Arthur Flexser <flexser at fiu.edu> wrote:
> 
> One thing to be aware of in testing TIMER's accuracy under Basic is that
> the break key check done between Basic statements occasionally causes
> interrupt processing to be omitted.  The clock "misses a tick" sometimes
> due to the fact that there are a couple of reads from $FF02 in Basic's
> POLCAT keyboard scanning routine that clear the IRQ flag.  If one of them
> occurs just at the right (wrong) time, the flag gets cleared before the
> interrupt can be processed and TIMER doesn't get incremented.  You should
> enter POKE&HADEB,&H39 before running your testing program to knock out the
> break key check.  You'll see that it makes a significant difference.
> 
> I think different CoCo's can vary by a few tenths of a percent in the
> timing rate.

A few decades ago I would never have believed I’d get a response from “the ADOS guy”. Thanks, Art! Very good to know!

		— Allen