[Coco] CoCo's TIMER and 60hz

Dave Philipsen dave at davebiz.com
Thu May 30 13:14:16 EDT 2019


It may not seem huge but that kind of drift relates to six minutes a day or three hours per month. If you’re rebooting the machine daily and setting the clock at each reboot it’s probably not a big issue but in a 24/7 environment it’s probably not acceptable.

If he really wanted to get fancy about it the 16-bit correction value could be stored in a register on the FPGA. The ISR would read the value from the register instead of RAM for calculating the correction interval and then when the graphics modes were switched the FPGA could automatically scale the value in the register to be correct for the particular graphics mode.

Assuming that the video signal from the matchbox is driving a multi-sync monitor it would be interesting to find out what different modes are being used.

Dave


> On May 30, 2019, at 9:17 AM, Allen Huffman <alsplace at pobox.com> wrote:
> 
> 
> 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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