[ntp:questions] ntpd on embedded risc

cnm3332 at gmail.com cnm3332 at gmail.com
Wed Feb 18 19:30:08 UTC 2009


On Feb 19, 11:32 am, Rob <nom... at example.com> wrote:
> Unruh <unruh-s... at physics.ubc.ca> wrote:
> > But a snapshot taken before the system has settled down to its long term
> > behaviour is especially useless. The way ntp works is that intially it
> > takes a while to settle down to its long term behaviour. With PPS control
> > it usually settles down to usec offset but it takes of order of 10 hours to
> > do so. Thus snapshots taken long before that are especially useless. If
> > after 10 hours the system still has msec offsets from a PPS then there is
> > something seriously wrong.
>
> He is not using a PPS in the sense that you are talking about.
> He uses the PPS support in gpsd which is written in user space and
> will settle to around 10us on a fast system that is not overloaded.
> On a slow embedded board it may be different, I have no experience
> with running gpsd on those.

The server is not running all the time, and it used on platform that
once
booted, which need accurate time within minutes.  We already run these
tools on a fast x86 machine, and it syncs very quickly and provides
very
good accuracy.  We are trying to migrate to the MOXA board, but
performance is much poorer.  I was more curious about things I could
configure so that NTP would be usable on this slower machine, even if
it took longer to get stable.  Should I look into increasing baud rate
of
serial, less polling interval, etc?  The linux distro is very small,
and provides
practically no tools, I'm not even sure how loaded the processor
becomes
with gpsd and ntpd.  Is there an effective way of checking that it is
not
too much for machine?  Thanks.




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