[ntp:questions] ntpd on embedded risc

Unruh unruh-spam at physics.ubc.ca
Wed Feb 18 21:12:26 UTC 2009


Rob <nomail at example.com> writes:

>Unruh <unruh-spam 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.

I will accept 10usec, which is way way better than 17msec. Again, if he was
connected for 10 hours ( well lets say 7 hr if your long term accuracy is
10usec) and he has 17 msec offset something is very wrong. If he was
connected on hour, it is to be expected. Thus, how long was he connected?





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