Good morning, José Daniel Muñoz Frías,
> I don't understand your problem. When an rt-linux task is started, it
> can not be preempted by any Linux task.
As I had understood, even RT-Linux remains multitasking, i.e.
at each sample hit -for a discrete time control- the running
task is preempted and the RT-control task starts after the
context switch. If this RT-task is finished, any other process
is scheduled by the dispatcher. At the next sample hit, the
RT-control restarts (T=discrete time, t= continuous time,
p= process):
T k k+1
t ||----------|---------|-----------|---------------||-------->
p preemption RT preemption any processes preemption
for RT process for any for RT
process processes process
Thus you can see, that for high frequencies, there is only
little space for the RT-process itself, because the preemtion
of the running process takes too much time -> trashing. The
introduced time delay is not desired with feed back control.
If however things with RT-Linux look like that:
T k k+1
t ||----------|---------|-----------||------>
p preemption RT wait RT
for RT process for next process
process starts sample hit resumes
and the RT-process takes over the machine without any
other process running, then I am content. Perhaps now
it is a little bit clearer, where my problems are.
ciao,
peterw
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Dr. Peter Wurmsdobler
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