copied from gpsd users list

Rick Bollar newsletters at bollar.com
Thu Mar 19 22:26:46 UTC 2020


Hi Paul,

Does using the "prefer" option force the local clock to be accepted?

I'm not on gpsd users -- I'll have to add it to my list. ;)

# PPS Server
refclock pps unit 0 time1 0 minpoll 0 maxpoll 0 refid PPS flag2 0 prefer

#Coarse Time GPS Server
refclock shm unit 1 minpoll 4 maxpoll 4 refid GPSD prefer stratum 1

Rick

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Thursday, March 19, 2020 5:00 PM, Paul Theodoropoulos via users <users at ntpsec.org> wrote:

> It's more relevant here. However, it wouldn't surprise me if every single
> person on this list is already subscribed to gpsd-users. Heh.
> 

> From Gary E. Miller gem at rellim.com:
> 

> Yo Paul!
> 

> On Thu, 19 Mar 2020 13:50:32 -0700
> Paul Theodoropoulos viagpsd-users at nongnu.org wrote:
> 

> > > The problem at hand is that a user has local PPS and wants that time
> > > to win the startup race, ahead of the more jumpy network chimmers.
> > > It is maybe 1,000x more accurate and stable.
> > > To that end, a user places the PPS at the top of the ntp.conf, with
> > > a short poll time than other refclocks, so that ntpd will select it
> > > first.
> > > But, when you add in a bunch of marginal pool servers, from all over
> > > the planet, and iburst them, then they win the race instead of the
> > > nice local PPS. ntpd starts out with the worst refclocks, not the
> > > best.
> > > Eventually ntpd will sort it out, usually, but best to just pick the
> > > local PPS on startup.
> > > So, if I may interject for my own clarity. For an ntp server with a
> > > properly running GPS and PPS, in a stable environment with reliable
> > > network, this would suggest that - regardless of poolor peer - it
> > > is best not to use iburst?
> 

> That would be my suggestion if normal startup quality is important to you.
> I can see a corner case where your PPS/GPS is dead, and you are still
> in a hurry to start. But even that is minimal if you have a good RTC.
> 

> Since most people only very rarely restart their stratum 1, not a big
> deal.
> 

> YMMV.
> 

> > As in, iburst is desireable for_client_ ntp devices, not for those
> > that are themselves stratum one?
> 

> That would be a good rule of thumb.
> 

> > (I'd like to copy this and its answer to the ntpsec list, since it's
> > most relevant there, if permissible)
> 

> Yeah, this whole discussion really belong there.
> 

> RGDS
> GARY
> 

> --------------------------------------------------------------
> 

> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
> gem at rellim.com Tel:+1 541 382 8588
> 

> Veritas liberabit vos. -- Quid est veritas?
> "If you can't measure it, you can't improve it." - Lord Kelvin
> 

> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> 

> Paul Theodoropoulos
> www.anastrophe.com
> 

> users mailing list
> users at ntpsec.org
> http://lists.ntpsec.org/mailman/listinfo/users

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