Re: [Qemu-devel] [PATCH] Choose emulated MIPS CPU at runtime

[Thiemo Seufer <ths@networkno.de>]

Stefan Weil wrote:
> Thiemo Seufer schrieb:
> > Looks very nice, except that the CPU models are out of touch with
> > reality. :-)
> > - There is no CPU called "R4Kc" etc.
> > - What Qemu emulates is currently close to a 4KEc with an R3000-style
> > FPU attached. (A 4KEc is a 4Kc with MIPS32R2 instructions.)
> There exists also an older 4KEc version which only supports
> MIPS32R1. AR7 (a SoC from TI) is based on this older version.

This can't be correct. 4KEc is defined as a MIPS32R2 core by MIPS
Technologies. A MIPS32R1 4KEc would be redundant since that's what
the 4Kc is.

> I noticed this because some code using DI worked well with QEMU,
> but my AR7 based DSL router crashed...

Did it die with an RI exception? If not then it sounds more like
a missing ehb barrier. Qemu doesn't emulate pipeline hazards...

> AR7, it would be nice to switch between MIPS32R1 / MIPS32R2
> instruction sets.

It would be nice to see a AR7 router emulation as a separate
machine type in Qemu. *hint* *hint* :-)

> I think this could be done similar to the FPU
> switch, but I don't have a list of the differences, and there are
> no MIPS32R2 markers in the QEMU code :-(

The specificiation for MIPS{32,64}R{1,2} used to be hidden behind a
"free registration" nag screen at http://www.mips.com/ . Unfortunately
it isn't ATM, it apparently fell through the cracks of the website
relaunch.


Thiemo