Re: [ECOS] Re: Ecos Port to PPC509/PPC555

[Sergei Organov <osv at Javad dot RU>]

I agree with every word in your reply. And I understand that eCos is
open source. I just wanted to make sure that if I begin work on FP
support, I will not do it in parallel with somebody else either inside
or outside Cygnus. Now when I've got exact answer, I'm going to
write down my thoughts how it could be implemented and post them here
for discussion. Hope I'll have time to do it next week.

Regards,
Sergei.

Jonathan Larmour <jlarmour@cygnus.co.uk> writes:
> Sergei Organov wrote:
> > 
> > I don't want
> > to have FP overhead for every task in my system. Actually only few
> > tasks should have floating point context, and the rest of tasks never
> > use floating point. Therefore it is required to somehow specify if
> > given task has FP context or not. This requires change(s) to the
> > kernel API. Optimizing further, if only some tasks have FP context,
> > then FP context switch is actually required only when control is given
> > to FP task. Such lazy FP context switch requires some support from
> > kernel and apparently some changes in HAL interface.
> 
> Yep. This is a sensible optimization, but yes it would require HAL changes.
> The clever thing is implementing an interface that won't affect other HALs -
> some MCUs will never have hard floating-point so we shouldn't be
> complicating their implementations unnecessarily.
> 
> It also has to be configurable because some interrupt/exception handlers may
> want to use FP of course.
> 
> > Overall, I'd prefer to have full FP support in eCos to be able to use
> > all possible tricks to get maximum performance from hardware. That's
> > why I asked about FP support in eCos - I meant general support, and
> > not FP context save/restore implementation for some particular
> > architecture. Sure, I can do all this myself, but then another
> > implementation will come from Cygnus. So the question remains.
> 
> Not if you contribute it back! If you want to propose something more
> concrete on this list, everyone can discuss it. Cygnus aren't working on it,
> but we will do what we can to help you do it. If you submit acceptable
> patches to the list, we will certainly incorporate it in future releases.
> eCos really is open source :-).
> 
> Jifl
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