Bob Feretich wrote:
> Thank you for the solution. Using Linux shm shared memory should have
> been obvious. :-[
>
> I was still thinking of Xenomai user tasks as running in a walled of
> environment. I've got to remember that when a rt user task is in
> secondary mode it has full access to Linux facilities.
>
> When my rt user task starts and ends it is in secondary mode. It can
> easily shmat() and shmdt() during these start and end periods.
Yes, and a process running Xenomai threads may also run non-Xenomai
threads, they will share the same memory, without needing to resort to
shared memories.
As for the shared memory, you may also use the POSIX interface:
shm_open/ftruncate/mmap/shm_close/shm_unlink
You may find it more convenient.
>
> As Philippe states, I just need to be careful about the synchronization
> method I use. The Linux process must never be able to block the rt task.
> (If the rt task wraps the buffer, we'll just throw away the history data
> until space becomes available and report a "data overrun" on the next
> block written.) As I said before, the buffer should be large enough so
> that never happens anyway.
You can use a FIFO, with a periodic non-rt thread polling one of the
FIFO's pointers. This would look a lot like what rt_printf does (file
src/rtdk/rt_print.c in Xenomai sources).
--
Gilles.
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