AW: AW: Dependencies of PPS API in rtems-libbsd

[Sebastian Huber]

On 30/03/2022 15:19, Gabriel.Moyano at dlr.de wrote:
>>> Ok, it seems the pps_event() could be called by interrupt service
>>> routines. In this case, you cannot use a mutex and condition variables.
>>> You have to use a thread queue directly. Use the thread queue ISR lock
>>> for mutual exclusion. Use _Thread_queue_Enqueue() to emulate sleep()
>>> and
>>> _Thread_queue_Flush_critical() to emulate wakeup(). Check all critical
>>> sections that they can be protected by an ISR lock (no blocking calls and short).
>> Is this even so if pps_event() calls signal or broadcast? Because pps_fetch() is the only function that is waiting (and locking a mutex).
> Do you mean something like this?
> 
[...]
> 
> Unfortunately something should be missing because it doesn't work.

In cpukit/score/src/futex.c you have a working example.

You would have to replace the mutex with the thread queue lock. I had a 
look at some FreeBSD drivers which use this stuff and it would not be 
possible to support them with this approach. You could move the

			if (abi_aware(pps, 1) && pps->driver_mtx != NULL) {
				if (pps->flags & PPSFLAG_MTX_SPIN) {
					err = msleep_spin(pps, pps->driver_mtx,
					    "ppsfch", timo);
				} else {
					err = msleep(pps, pps->driver_mtx, PCATCH,
					    "ppsfch", timo);
				}
			} else {
				err = tsleep(pps, PCATCH, "ppsfch", timo);
			}

and

	/* Wakeup anyone sleeping in pps_fetch().  */
	wakeup(pps);

blocks into RTEMS-specific sleep/wakeup callouts in struct pps_state.

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