[ntp:questions] Stick to PPS, even if the prefer server fails

Dave Hart davehart at gmail.com
Wed Mar 25 22:54:15 UTC 2009

On Mar 25, 9:19 pm, Unruh <unruh-s... at physics.ubc.ca> wrote:
> I have no idea why and whether kernel PPS code is any better ( or worse)
> than say PPS discipline using the shm PPS refclock using parallel port
> interrupt. Ie, both can discipline
> to about 1-2usec level.

Re-read the thread, then.  A kernel clock disciplined by PPS allows
PPS to continue to discipline the clock when ntpd's PPS implementation
stops doing so because of a prefer peer problem.

> The main problem is that the ntp model is too slow
> reacting to temperature induced drifts.

I'm sure that's your main problem re ntpd, but it's completely
tangential to the thread.

> >The complete system doesn't serve time to others. It's intention is
> >monitoring. I'm building this as a diploma thesis for a
> >telecommunication company. They have a large number of ntp servers
> >with GPS receivers (called SSU) across the country. So my system only
> >watches the offsets, that these SSUs have to assure that they are OK.
> They can monitor only to the msec (or 1/10 msec)  level unless the other systems are at the same place.

I think he's monitoring the self-reported offsets between the NTP
disciplined clock and the local GPS receiver.  Network delay would not
be a factor if so.

Dave Hart

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