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Date: Fri, 20 Jun 2008 16:42:00 +0200
From: Philippe Gerum <rpm@xenomai.org>
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Sender: Philippe Gerum <philippe.gerum@domain.hid>
Subject: Re: [Xenomai-core] [PowerPC] Registers Corruption at Context Switch
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To: Benjamin ZORES <benjamin.zores@domain.hid>
Cc: xenomai-core <xenomai@xenomai.org>

Benjamin ZORES wrote:
> Philippe Gerum a =E9crit :
>> See arch/powerpc/switch_32.S, rthal_switch_threads(), for the part that =
does the
>> actual stack switching.
>>
>> Note that this code is obfuscated by the fact that we have to handle so-=
called
>> "hybrid" switching, between Xenomai kernel threads (which do not rely on=
 a
>> task_struct), and Linux tasks (Xenomai userland, Linux kthreads, or regu=
lar
>> userland Linux). Fortunately, what is saved on the stack in any case is =
easy to
>> find out.
>>  =20
> Thx for the info.
> Can you tell me why GPR registers would be saved there and FPU ones in=20
> another function ?
>=20

Because FPU management with Xenomai involves additional handling, e.g. FPU =
state
fixup during primary/secondary mode switch, Linux to Xenomai real-time
transitions. That support has to be provided independently from the pure ta=
sk
switching code.

--=20
Philippe.