68020 in UNIXpc

[John B. Milton]

Arrrrrrrrrrrrg goofed the first edit and lost it.

I would suppose that a 68020 or 68030 could be added to a UNIXpc on a
dauter board. The real problems come in the differences between the
two (or three) processors software wise. All the 68k series CPUs have
different exception stack frame formats. Some '020s don't even have the
same format. This is controlled by pushing a frame version number. I
suppose one would use this in a multi-processor '020 machine where all
the '020s don't have the same version number.

Getting back to reality, or however much there is at 4 am in the morning.
I think it could be pulled off with a somewhat slower virtual machine approach.
The kernel would actually run in user mode and there would be an outter
'020 layer running in supervisor state. When an exception occures, the
'020 supervisor mode code creates a 68010 format exception stack frame and
then jumps to the regular 68010 exception table. The return from exception
instruction causes a priviledge violation and it's back in the '020 code.
And on and on.

The major problem is writing this beastie without access to the current
kernel code. Another problem is getting the '020 code running. This could
probably be done with a replacement boot loader or a pre-boot loader. I
think all this is doable. The performance increase would not be too good
until things are re-compiled with a 68020 compiler. Gcc sounds good for this.

I'm sure there are a lot of little, very important things I'm missing.
Ok folks, what are they?

John
-- 
John Bly Milton IV, jbm at uncle.UUCP, {ihnp4|osu-cis}!n8emr!uncle!jbm
home: (614) 294-4823, work: (614) 459-7641; talk to me about fractals