Your math is correct. The 62.5 us period comment was copied and pasted from an example I found somewhere, and I never bothered to verify even though I have a 1024 prescaler in the diy-ltcc code that is showing the correct time period.
The 1.792 ms / 28 ticks may need more fine-tuning. I found that when the controller was writing to a file without echoing a bunch of debugging noise to the console, this value had to be increased. In other words the time involved in sending to the console was creating a delay that has to be accounted for in order to get the fastest acquisition rate. Sd card write latency is another factor (though much smaller).
I'm sure it could be adapted to work with the PCM as bus master, but I don't see myself having the ambition to take this to that level. I have a date this winter with a d/a, a crap-ton of sandpaper, primer, paint, etc. I'll probably put a page up on my wordpress site for it and link to it from my .sig. but that might be as far as that goes.
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