pkarashchenko commented on pull request #5424:
URL: https://github.com/apache/incubator-nuttx/pull/5424#issuecomment-1030880794
> It's just because you start the POSIX timer at the same time of schedule
timer interrupt(10*n in above example).
It does not matter when I'm starting a timer. This change is not about timer
start, but about timer reschedule that is done in SYS Tick ISR handler, so it
is always in sync with timer interrupt.
> You can try to start your POSIX timer in a GPIO interrupt handler, toggle
the GPIO by hand, and measure the result. In most case, you will see what I
describe here, because GPIO can happen randomly in one tick
period(0ms-9.9999ms).
I will try, but I can ensure you that it will be the same. But I will make a
test with real HW and send you a picture from the logic analyzer.
BTW my programs look like:
```
int periodic_main(int argc, char *argv[])
{
int ret;
timer_t timerid;
struct itimerspec time_value;
struct sigevent ev;
struct siginfo value;
sigset_t set;
ret = timer_create(CLOCK_REALTIME, &ev, &timerid);
if (ret < 0)
{
syslog(LOG_ALERT, "ERROR: timer_create() failed: %d\n", errno);
return EXIT_FAILURE;
}
/* Ignore the default signal action */
signal(SIGALRM, SIG_IGN);
/* Set up a signal to wake-up periodically */
time_value.it_value.tv_sec = 0;
time_value.it_value.tv_nsec = 30000000;
time_value.it_interval.tv_sec = 0;
time_value.it_interval.tv_nsec = 30000000;
ret = timer_settime(timerid, 0, &time_value, NULL);
if (ret < 0)
{
syslog(LOG_ALERT, "ERROR: timer_settime() failed: %d\n", errno);
return EXIT_FAILURE;
}
for (; ; )
{
/* Wait for a signal */
sigemptyset(&set);
sigaddset(&set, SIGALRM);
ret = sigwaitinfo(&set, &value);
if (ret < 0)
{
}
else
{
/* Perform periodic action here */
}
}
return 0;
}
```
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