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Originally Posted by Toni Wilen
Hahaa, it is real hardware bug, but not in ALARM == TOD comparator. TOD incrementation logic is buggy
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Nice find
How old is the 8250 design and this is only uncovered now
A couple of questions spring to mind:
- you tested TODMID; does the bug also happen with TODLOW and TODHI? I think TODLOW is OK, or your test program would have stopped at TOD=0x000010.
- does it happen (to any byte) at other xF->x0 boundaries like 0x1F->0x20, 0x2F->0x30 etc. ? 0xFF->0x00 ought to be interesting to test at least
- does it happen on CIA-A as well?