Reply 40 of 66, by Deunan
Skip94 wrote on 2022-02-22, 06:46:The modified POST 4 seems to work exactly as expected, holding on C0,--, then 00,C0, before running the test as before.
Nope, that actually failed the sanity check. The first code should be C003, not C0--, which mean the first write failed to register on the POST card. That really should not happen, I've been using similar code on 386 and 486 mobos without such issues. But I do know the POST cards can be slow to process the I/O writes for some reason, perhaps due to oversimplified signal decoding.
So here's yet another POST4 variant. This time I've added ~20ms delay loops before and after every access to POST card. I mean it could be down to the problems your mobo has, but we need reliable readouts. Without that the results will be always confusing. If we can't use the POST card, maybe we can take advantage of the serial ports on your mobo. I assume you have another PC with serial port input, or RS232 to USB dongle? For that I need to brush up on low-level 8250 init code, it's been quite some time since I last did anything of the sort.