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

[Thiemo Seufer]

Hervé Poussineau wrote:
> Hi,
> 
> This patch uses the new "-cpu" command line option, to choose the CPU at
> runtime (R4Kc/R4Kp and FPU/no FPU)
> The model can be extended to emulate more accurately some CPUs.
> 
> This removes the MIPS_USES_FPU compilation time option, and replaces by a
> runtime one.
> 
> Please comment.

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.)
 - 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

Does this sound reasonable?


Thiemo