AW: AW: [PATCH 1/1] kern_tc.c: th_generation starts with 1 after overflow for single-core

[Sebastian Huber]

On 30/05/2022 08:29, Gabriel.Moyano at dlr.de wrote:
>> On 27.05.22 11:49,Gabriel.Moyano at dlr.de  wrote:
>>>> On 27.05.22 10:51, Sebastian Huber wrote:
>>>>> Hello Gabriel,
>>>>>
>>>>> the uniprocessor version uses an optimization at the reader side:
>>>>>
>>>>> #if defined(RTEMS_SMP)
>>>>>        } while (gen == 0 || gen != th->th_generation); #else
>>>>>        } while (gen != th->th_generation); #endif
>>>>>
>>>>> This is possible since the windup happens with interrupts disabled.
>>>>> I guess you need this optimization somewhere in the PPS/NTP code.
>>> Yes, you are right that is for the PPS code.
>>> The value of th_generation is saved in pps_capture() and I shouldn't add a while waiting it to be different that 0 there.
>>> If its value is 0, then the pps_event() returns early.
>>> This is something that could happen in very particular circumstance (pps event happens when the th_generation is 0).
>> In uniprocessor configurations, we don't need the 0 special value. It is only required in SMP configurations since one processor may
>> observe a timecounter update which is in progress on another processor.
> Being that case, the easiest solution will be to not check if pps->capgen == 0  in pps_event() for uniprocessors configurations.
> 
> /* If the timecounter was wound up underneath us, bail out. */
> #if defined(RTEMS_SMP)
> 	if (pps->capgen == 0 || pps->capgen !=
> #else
> 	if (pps->capgen !=
> #endif
> 	    atomic_load_acq_int(&pps->capth->th_generation))
> 		return;
> 
> what do you think?

Sounds good if it makes your test case passing.

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