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

[Sebastian Huber]

On 31/03/2022 12:10, Gabriel.Moyano at dlr.de wrote:
>> 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.
>>
> 
> Just reading this email a second time, do you mean stop trying the thread queue approach and use another RTEMS-specific solution for waking up tasks which wait in pps_fetch()? For example use RTEMS signals or events?

Yes, I would stop trying the thread queue approach. It is not flexible 
enough for libbsd support. With the sleep/wakeup callouts in struct 
pps_state, the drivers (for example in libbsd) can use a synchronization 
mechanism at their choice.

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