[ntp:questions] What is the NTP recovery time from 16s step in GPSserver?

David Lord snews at lordynet.org
Thu Nov 1 09:27:33 UTC 2012

David Taylor wrote:
> On 31/10/2012 21:04, unruh wrote:
>> On 2012-10-31, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
> []
>>> NTPD is a "slow starter"!  Ideally, you will only start it once and
>>> let it run for a few months.
>>> How slow is a "slow start"?.  It can take NTPD up to ten hours to
>>> synchronize within + or - 50 nanoseconds with whatever you are using as
>> It will never get to within 50nsec. The interrupt processing is far more
>> variable than that. You might get to withing a few micro seconds.
> On a recent restart from cold, the server here took about 15 minutes to 
> get to within 250 microseconds, and about an hour to be within 10 
> microseconds.  Ultimately it is within about 3 microseconds.

I'm on NetBSD-6 and ntpd 4.2.6p5 although I don't believe the
previous versions were any worse. The rstarts are usually within
around 15-30 min to be better than 1 ms and replying to requests.
I lost 7 x pcs Jun-Sept this year after local mains substation
transformer self destructed so my system with GPS is down. That
would be within a few usec within an hour but was sensitive to
large temperature and load changes with nightly excursions to
30 usec for short periods.

The example I've seen as to getting sub usec was GPS combined with
a remote stable system clock source (from a TAPR board). I've too
much on at the moment repairing/replacing the failed systems to
setup the Ru clock I bought off ebay.


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