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Re: powerpc altivec support



On Tue, 2005-02-08 at 15:52 -0800, Till Straumann wrote:
> Hi.
> 
> I'm looking into ALTIVEC support for RTEMS along the lines of
> lazy FP context switching. However, I'd like to hide this from
> SCORE code for obvious reasons. OTOH, it seems also ugly
> to switch the vector registers as a side effect of CPU_Context_switch().
> 
> Any suggestions?
> 
> Ralf: what needs to be done to get an altivec enabled toolchain and
> newlib for the CPU variants that support it?
Basically, by adding appropriate multilib variants to GCC.

In general have to prove that such a multilib variant actually makes
sense (gives a measurable improvement in performance) 
and can not be avoided by other means.

However, due to the number of multilib variants being used by the
powerpc, convincing me to add another one to powerpc-rtems-gcc will be
extraordinarily tough.

> BTW: I see in gcc/config/rs-6000/t-rtems (gcc-3.2.3 / rtems-4.6) that
>            "no-eabi" is passed to all PPC variants (MULTILIB_EXTRA_OPTS)
>            -- this might be out of sync, as EABI is the default PPC abi for
>            RTEMS

Is it? That's news to me, but ...

cf. http://www.rtems.org/cgi-bin/gnatsweb.pl?cmd=view&pr=195

... nobody ever has been able to sort this out.

>  [score/cpu/powerpc/rtems/score/ppc.h says:
[This file is obsolete, score/cpu/powerpc/rtems/score/powerpc.h has
replaced it.]

> /*
> *  Default to the EABI used by current GNU tools
> */
> 
> #ifndef PPC_ABI
> #define PPC_ABI PPC_ABI_EABI
> #endif
> ]
> 
>             and I believe nobody ever defines this to something else.
:-) Cf. http://www.rtems.org/cgi-bin/gnatsweb.pl?cmd=view&pr=195

Ralf