Re: [Qemu-devel] MIPS COP1X (and related) instructions

[Richard Sandiford <rsandifo@nildram.co.uk>]

Thiemo Seufer <ths@networkno.de> writes:
> Richard Sandiford wrote:
>> All MIPS COP1X instructions currently require the FPU to be in 64-bit
>> mode.  My understanding is that this is too restrictive, and that the
>> base conditions are different for different revisions of the ISA:
>> 
>>   MIPS IV:
>>     COP1X instructions are available when the XX (CU3) bit of the
>>     status register is set.  This bit can be set independently of
>>     UX and FR, and controls the core MIPS IV instructions as well
>>     as the FPU ones.
>
> This part is, sadly, not fully correct. It depends on the CPU
> implementation what effect, the CU3 bit has. IIRC it behaves on some
> CPUs as you describe, while it is a nop on others.

Sorry.  I'll take your word for it.

> (I don't know offhand which CPU did what there.)

(FWIW, the r10k and VR5500 do as described, and I'm pretty sure the
RM7000 and RM9000 did too.)

> Looks reasonable to me, apart from that one misassumption.

What should the patch do instead for MIPS IV?  Enable them unconditionally?

Richard