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Date: Tue, 06 Mar 2007 20:18:56 +0100
From: Stefan Weil <weil@mail.berlios.de>
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Subject: Re: [Qemu-devel] [PATCH] Choose emulated MIPS CPU at runtime
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To: qemu-devel@nongnu.org

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.
I noticed this because some code using DI worked well with QEMU,
but my AR7 based DSL router crashed...
For AR7, it would be nice to switch between MIPS32R1 / MIPS32R2
instruction sets. 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 :-(
> - MIPS Technologies "4Kc" and "4Kp" have both no FPU support at all,
> they are also 32bit only. (IIRC the difference those two is that
> the 4Kp has only a fixed mapping MMU, the 4Kc has the real thing.)
> - For a Jazz/Magnum-like CPU we should add a "R4000" or probably
> a "R4400". This CPU is 64bit and has always a FPU.
> - For the Malta I plan to go for a 34Kf, but that lacks a few bits for
> now.
>
> So, to make some sense out of it:
> - Qemu "4kc" machine, 32bit, no FPU: 4Kc or 4KEc
> - Qemu "4kc" machine, 32bit, with FPU: 24Kf
> - Qemu "4kc" machine, 64bit, with FPU: R4000, this should become a
> separate machine.
> - MIPS Malta, 32bit, no FPU: 4KEc
> - MIPS Malta, 32bit, with FPU: 24Kf
This looks good. I'd add one more for QEMU with AR7 support:
    - AR7 machines, 32bit, no FPU, 4KEc with MIPS32R1 only
>
> Does this sound reasonable?
I ask the same question.

Stefan