jeffpar/pcjs.v1

386 SS has wrong behavior after reset

Octocontrabass opened this issue · 1 comments

Octocontrabass commented

When the 386 is reset, the SS register has a value of 0 but SS behaves as if its base is nonzero. On a real 386, SS.base is set to 0 after reset. (...As far as I know. It does point to RAM, but I haven't verified exactly where.) Actually, upon further investigation, I think the issue is actually that SS is a 32-bit segment after reset, because stack operations are updating ESP instead of SP.

The code that tripped this bug reset the CPU using the keyboard controller, like below. I haven't tested what happens if the CPU is reset any other way.

MOV AL, 0xFE
OUT 0x64, AL

I found the bug while I was using this machine in Firefox on Windows.

Let me know if you need anything else.

jeffpar commented

Will do. What you suggest sounds plausible, but it'll require some debugging, because just looking at the resetRegs() code path, I don't see the problem yet.