> I need to schedule several "tasks" that I envision as running in the
> user-space (they really need no kernel-access or services) which have to
> run on a hard realtime basis (In truth, the actual requirement is that they
> run at a "fixed rate" but there is considerable jitter allowed as long as
> no periods are missed.
>
> Can I simply (following the examples) turn a user-space function into a
> real-time task and then make it periodic? If not, then what's the best way
> to get a kernel-space task to "trigger" the user-space functions?
I'd use the FIFO interface for that I think. From the rt-program you can
"post" a trigger-message (a byte perhaps) to an agreed upon FIFO. Your
user-space program will have tried to read from the FIFO and should be
PENDING on data arriving from it. When your user-space program tried to
read the FIFO it would have been suspended until data (trigger) arrives
when it would have been rescheduled to complete the I/O operation on the
FIFO (trigger).
The method described above is good for many things, but not all. The FIFO
will queue up triggers and the rt code and the user code could get out of
sync in realtime.
- C W Wright
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