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Ok, as I mentioned in my test request for my kernel, the VBE driver just doesn't want to work on my test machines. It works in QEMU, my friend's laptop, and on an ATI Rage128. But, my main machine and my test machine, both with nVidia cards, just switch the screen to standby when I try to switch mode. I've double checked the VBE code, checked it against the VBE specification, and double checked that the V86 code is doing the right things for the emulated instructions. I can't for the life of me figure out what's causing it. Anyone else experienced this or know what it could be?

My VBE code is here and my V86 code is here

please, have you been able to solve your problem? In that case could you explain us how you managed to get it work?
Thank you

Yes, I managed to resolve it. The issue was that the I/O permission bitmap in the TSS was set up incorrectly so that some I/O instructions weren't working correctly.

thank you very much for this answer!
in my case, i get a debug exception, i think there is some kind of memory corruption! But i'll try to use a I/O bitmap. What port should i enable?