Tomasz Motylewski wrote:
> I guess VT does not use FP, xterm (and Xserver) do use it.
That's why you have to tell your real time scheduler that also Linux is
using the FPU. In fact the real time task swithching is optimized in
such a way to avoid saving/restoring the FPU if only one real time task
is using it.
Recall that from RTL/RTAI point of view Linux processes are just many
threads of execution of a single very low priority real time task, i.e.
Linux. So if Linux is using the FPU and the real time scheduler is not
notified its use Linux processes FP calculations are disrupted.
Note also that gcc often uses the FPU to translate to integer numbers in
the form 1E6. So never use 1E6 if you mean it to be 1000000. A more
subtle thing that gcc does is using available floating point registers
also when no FP operation is involved. It can create a lot of, behind
the curtain, troubles. Your system works but is causing a lot of hidden
traps and your need for a precise timing goes ashtray.
Ciao, Paolo.
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