On Tue, 2011-04-19 at 11:29 +0200, Philippe Gerum wrote:
> 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.

A nop in fixing the issue, I mean.

-- 
Philippe.



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