On Aug 30,  6:09pm, Simon Burge wrote:
> Looking through the on-line R4000 user manual, I would guess that we'd
> also need to set UX in the status register as well.  The only reference
> to the UX bit in NetBSD is the definition in mips/include/cpuregs.h.
> Maybe Ultrix is not setting this as well - it would explain the illegal
> instruction I was getting.

  If the UX bit is set, that means the user mode is running is 64 bit mode -
which includes 64-bit addressing.  This would require some rather significant
changes to the kernel.  It would also mean that the entire userland would
have to be compiled for 64 bits (and would no longer run on mips1 processors),
unless someone wants to try to support mixed 32/64 bit user mode.  [That would
get rather nasty - the kernel would have to support both 32 bit and 64 bit
processing of usermode addresses, and there would have to be two different
versions of libraries for each mode.  I wouldn't even want to attempt it!]

  I'm almost certain that Ultrix can't support 64 bit usermode, and would
make a guess that Ultrix very likely doesn't even support 64 bit FP registers.
The -mips3 option on the Ultrix compiler doesn't appear to affect the GP or
FP register size.  I'd guess that -mips3 only means to use mips3 instructions
that are valid in 32 bit mode.

Michael

-- 
Michael L. Hitch			mhitch@montana.edu
Computer Consultant
Information Technology Center
Montana State University	Bozeman, MT	USA