PowerPC FP handling weakness.

[Sergei Organov]

Eric Valette <valette at crf.canon.fr> writes:

> Sergei Organov wrote:
[...]
> > Yes. RTEMS doesn't have "on-demand" FP context switch. Only "deferred" context
> > switch. I.e. switch context only when new task is marked to be "floating
> > point" and doesn't already own the FP context.
> > 
> 
> Yes but on-demand FP context switch is rather easy to implement since we
> now can handle the FP unavail exception. We just need to know to wich
> thread the current FP context belong and store/restore it.

Your are right, but on-demand switch has its own drawbacks. One unfortunate
thing is that FP bit and interrupt enable bit are in the same MSR on PowerPC,
and this brings troubles with _ISR_Disable/Enable when on-demand FP context
switch is used (see my previous mail for details).

BR,
Sergei Organov.