You wouldn't really do this from application level, right? There is
currently no POSIX-compatible application interface to do that. But you
could implement a kernel thread that is started in your board
initialization logic that can call clock_synchronize() according to
whatever criteria you need.
I suppose a standard kernel thread could also be implemented in
sched/clock if such a one-size-fits-all solution can be imagined. You
might check out logic in sched/clock for CONFIG_CLOCK_TIMEKEEPING. That
is used primarily for adjusting the time to properly track time from
NTP. Seems to me that that is essentially the same issue: Keeping two
clocks in agreement.
On 3/20/2023 4:20 PM, Michal Lenc wrote:
Hello all,
NuttX offers a function clock_synchronize() that synchronizes system clock
with clock from RTC (internal or external). The synchronization is done
during board initialization and I suppose this can also be called from an
application level if required. However I was not able to find any
implementation that would automatically synchronize system time with
(correct) values from RTC if system clock drifts from real time. It seems
the only possible option is to "force" the synchronization by calling the
mentioned clock_synchronize() function periodically from application level.
What is your view on adding some sort of automatic synchronization that
would ensure system clock stays in sync with RTC (or at least error is less
than some value) even when i drifts away from "real time"? Quite simple
solution is to let clock_gettime() to update base time after N reads however
this would add some computation complexity to gettime (I2C communication
delay for external RTC etc.) and I am not sure if we really want this inside
clock_gettime().
Best regards,
Michal Lenc
