Okay. This time my small server got screwed up. Totally. segfaults at no apparent reason, lags, and finally the PC not starting at all. Since ssh was down, I had to debug using a UART and a POST card (No monitor in the closet where it stands usually). In the end I had to take the small thing out of its place to the table. A detailed analysis showed up that it was the RAM. Luckily I had a spare 2 GiB chip around and popped it in. However, while troubleshooting it, I hooked the POST card…
The last thing gave me an idea. Not sure if that was done before.
Theory:
The POST card shows data from 80h adress where BIOS stuff writes the codes. Once the system has booted, BIOS doesn’t touch it.
Question:
Can the userspace software write something there?
Implementation:
I didn’t see any reasons why no, so while the backups were untarring to the HDD, I quickly threw a small piece of software (github link).
And it worked awesomely. Obligatory video:
What i got is a small utility to control a POST card from userspace. Basically, I can now troubleshoot bootscripts, and whatever stuff I want using a POST card. Not sure it has a big practical purpose, but it was still fun enough.
You could use for GPIO output on any standard PC, got a nice 8bit bus there you could use to drive a heap of devices.