NEC V20 optimized Book 8088 bios crashing about 8088_bios

[ssvenn]

No I haven't tried checkit, but I can flash the V20 version again and do some more comparisons tomorrow. The BIOS does report Main Processor: NEC V20 during boot.

I can test some more eeprom chips too in case something weird is happening with the programmer. I'm using a minipro tl866cs and it verified the winbond 27c512 chip fine after writing both times.

[ssvenn]

Ok I've flashed the V20 optimized rom to a new chip and was unable to reproduce the issue, everything works fine now... I've also reflashed the chip that I had the problem on initially and can't reproduce it on that one either. Both BIOS versions pass all the checkit tests too.
So I'm thinking the problem was the eeprom or the programmer, these are used chips from ebay that came with random data on them but it seems to have cleared up by programming them a couple more times. It was still weird that it worked for text mode but crashed when switching to graphics modes! :)

[skiselev]

The only difference between V20 version of the BIOS and the 8088 version is the XT-IDE BIOS extension flavor - with and without V20 instructions respectively. There are no differences in the BIOS, and it uses exactly the same binary image.

I am wondering if at boot the system identifies the CPU as NEC V20?
I'd expect many more things to fail if the CPU is faulty. So it is definitely a weird and interesting issue.
Have you tried running diagnostic software like CheckIt?