On Tue, 2011-04-19 at 10:42 +0200, Gilles Chanteperdrix wrote:
> Philippe Gerum wrote:
> > On Tue, 2011-04-19 at 09:58 +0200, Jesper Christensen wrote:
> >> Great thanks, but i can't help wondering if the problems i'm seeing are
> >> related to some of my userspace programs using fp.
> > 
> > I don't think so. The switchtest programs exercises the FPU hardware in
> > a certain way to make sure it is available in real-time mode from kernel
> > space (which is an utterly crappy legacy, but we will have to deal with
> > it until Xenomai 3.x). As far as I can see from your .config, you can't
> > have such support, so switchtest was basically trying to test an
> > inexistent feature.
> 
> In fact, switchtest whether Xenomai FPU switch routines work when the
> Linux kernel itself uses FPU in kernel-space. Currently, the only place
> when this happens is in the RAID code: x86 uses mmx/sse, and some power
> pcs use altivec. Some powerpc also fix unaligned accesses to floating
> point data in kernel-space, I do not know if this may interfere, which
> is why the powerpc code is compiled even without RAID.
> 
> 

AFAICS, fp_regs_set() on ppc is issuing a load float instruction in
kernel space which could be unaligned, and therefore trap. Looking at
the .config for the target system, hw FPU support is disabled in the
alignment code, so basically, this would beget a nop.

-- 
Philippe.



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