[ntp:questions] nmea and initial large offset

Kalle Pokki kalle.pokki at iki.fi
Wed May 5 17:44:38 UTC 2010


On Wed, May 5, 2010 at 16:44, Andy Helten <andy.helten at dot21rts.com> wrote:
>
> Yes, this is exactly right.  We worked around this problem in our system by
> grabbing the time from the refclock, setting system time with the refclock
> time, quick sync NTP, and then finally start the NTP daemon.

This is probably the only possible workaround without modifying NTP
code itself. However, in a vehicle that boots and starts all
operations in a place without GPS coverage, this also becomes quite
impossible to arrange properly.

The funny thing is that the exact date is provided by e.g. the SHM
refclock driver, but the year information is intentionally discarded
when the timestamp propagates up towards the NTP core code. Then the
code does all kinds of heuristics to guess the correct year, but is
unable to do that if the clock is off by more than four hours.



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