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Date: Wed, 11 Jun 2008 14:37:36 +0200 (CEST)
From: "M. Koehrer" <mathias_koehrer@domain.hid>
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Subject: Re: [Xenomai-help] Are xmm-registers saved with a (task) context
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To: gilles.chanteperdrix@xenomai.org, mathias_koehrer@domain.hid
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Hi Gilles,

thanks for your response.
With the MMX registers, you are right. They are actually aliased with the F=
PU registers.
However, the XMM registers (SSE, SSE2) are not aliased.=20
The aliased MMX registers AND the not-aliased XMM registers are available w=
ith today's CPUs,
i.e. you still have to take card when using MMX registers.
(All information according to Intel's 64 and IA-32 Architectures
Software Developer=92s Manual, Volume 1, Chapters 9,10,11)

>>From your mail before I assume that the (not-aliased) XMM registers are sav=
ed with the switching routine
and can be used without have to save/restore them.

Regards

Mathias


> > The xmm register are saved by the FPU switching routines. Note
> > however, that depending on the x86 you are using the xmm registers are
> > aliased to the FPU register or are separate registers. So, on machines
> > where the xmm registers are aliased to normal FPU registers, you have
> > to do the save restore on your own if you want to use MMX, SSE, or
> > SSE2 and use FPU instructions in the same thread.
>=20
> This probably applies to very old CPUs, xmm are separate registers now.
>=20


--=20
Mathias Koehrer
mathias_koehrer@domain.hid


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