Hi all,

I posted this over at cpu-world.com as well, but it was suggested to me to post it here. So here goes:

TL;DR: Has anyone attempted to add any of the missing 486 instructions to the Hypercode for the nx586? Specifically INVD, INVLPG and WBINVD?

Long story:
I am on a foray to install NetBSD on all kinds of weird old hardware, and as of quite recently there exists a patch set to restore support for FPU-less x86 systems. This works fine on an IBM486SLC system, which is essentially a 386SX-class sytem (16-bit bus, 387 FPU if any).

My NexGen VLB board (P90) seemed to be a really good candidate, because it's missing the FPU but is otherwise very fast (compared to the 486SLC) and can have a ton of memory (again, compared to the 486SLC).

Alas, as stated in this post, even with "alternate instructions" enabled in BIOS, several 486 instructions are still missing.

Booting any modern version of NetBSD fails early, usually resulting in an instant reboot the moment the kernel starts executing. In a very old NetBSD, v4.0.1 (current is 10.1), it actually says the failing instruction is INVLPG - this may or may not be the same thing that causes the reboots in newer versions; having a kernel debugger embedded in the floppy kernel images is a luxury after all.

Seeing Herbert Oppmann's fantastic information, it looks like it might be theoretically possible to add support for the missing instructions. Has anyone ever attempted to do this (or otherwise fix bugs left there from NexGen's heyday)?

Thanks for reading, and have a good one!
/Eirik