Jan Kiszka wrote:
> Hi,
> recent announcement of some new TSC synchronisation feature in RTAI made
> me stick my nose into this and think about the whole issue of clock
> synchronisation again. Well, let's not talk about RTAI details here, but
> they got one thing right: as long as we cannot handle unsynch'ed TSC on
> SMP, we need some detection and alarming as the bare minimum.
> Why can't we handle such cases yet? First, there seems to be still some
> bugs hidden in the core (one example: xntimer_start_aperiodic() uses the
> local time stamp to start a remote timer).

Reading the code, there seem to be only two places where the local tsc
is used to set a remote timer, it is xntimer_start_aperiodic, and
xntimer_move_aperiodic, which is used by xntimer_migrate. So we are left
with only one bug: starting a timer on the remote CPU, this could easily
be implemented with a queue which would be handled by the timer IPI.

> (...)
> for smoothly adjusting clocks during runtime would be great. I'm
> thinking about a generic infrastructure to synchronise the Xenomai time
> on external sources (=>distributed clocks).

What do you want, NTP ? Or calling xnpod_settime periodically ?

                                                 Gilles Chanteperdrix

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