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Re: [PATCH] Support for MIPS R5900 (Sony Playstation 2)
On Tue, 8 Jan 2013, "Jürgen Urban" wrote:
> > As a side note -- I've noticed elsewhere in this change that the R5900
> > supports single-precision FP only. This is similar to what the
> > R4640/R4650 does (up to supporting 32 single registers in the FR mode --
> > is that any different to the R5900?), however up till now we did nothing
> > explicit for such a setup, except from respecting the -mfp32 option.
> > This change introduces extra bits however, like hardwiring -mfp32 --
> > perhaps they could be generalised in some way to cover the R4640/R4650 as
> > well? -- again, for consistency.
> The patch for R5900 currently sets -mfp32 with the line:
> if (mips_opts.arch == CPU_R5900)
> mips_opts.fp32 = 1;
> This avoids updating the FPU to 64 bit when setting higher mips ISA level.
> The R4640/R4650 can be added here. Is this what you want?
I've thought of a more general approach, for example marking the missing
instructions to support the unimplemented double format for the
R4640/R4650 as well (or perhaps the other way round -- whenever -mfp32 is
active rather than for any specific processor, as otherwise these
instructions are in a sense valid, as the MIPS FPU by definition allows
deferring any operation to software emulation). There may be something
In any case, please don't feel compelled to make these changes -- unless
you really want to. I just raised it as a general point in discussion.