[ECOS] FPU support implementation question.

Sergei Organov osv@javad.ru
Tue Apr 11 08:04:00 GMT 2000


Hello,

I'm implementing FPU support in the PowerPC HAL and have a design dilemma that 
I'd like to discuss.

I have working version that is modeled after the MIPS HAL. Now I'd like to
start to implement advanced FPU support that will switch FPU context on
demand. This requires that FPU state is stored not in the CPU context as it is
now, but in some other place that is pointed to from the CPU context. The
on-demand FPU context switch will be a configuration option, and if it is
disabled, then current simple implementation is active. For simplicity I'd
like to still save FPU context outside of CPU contex even if the on-demand
option is disabled. Compared to the current implementation this approach adds
additional overhead of dereferencing pointer on every context save and
restore. I believe the overhead is actually small and could be ignored.

Any comments?

Thanks,
Sergei.



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