Raspberry Pi NTP config with fudge factors

[Gary E. Miller]

Yo Frank!

On Thu, 5 May 2016 19:41:07 -0400
Frank Nicholas <frank at nicholasfamilycentral.com> wrote:

> I haven’t used the NTP configuration below for years.  I came up with
> it from some recipe(s) I found online (some commented in the file).
> The "time2 0.350" was the generally accepted best number for the
> original Raspberry Pi A/B.  I personally have no idea how to tune
> NTP.  I just used what I thought was the best information I could
> find at the time.

Easy with the 28 refclock.  Not sure on the 20.  DO you even see the 
coarse time with ntpq -p?


> My current NTP server is part of pfSense (FW/Router/NTP/etc., based
> on FreeBSD-10.3-RELEASE)  Their web interface is limited in some of
> the NTP/PPS/GPS settings you can easily get to.  If you make changes
> outside the web interface, you risk them being overwritten by the web
> interface.  I really need to get a good config nailed down & not
> touch it.

Once you have it how you like it, you only touch it for IP changes.

> > On May 5, 2016, at 7:12 PM, Gary E. Miller <gem at rellim.com> wrote:
> > 
> > I use the 28 refclock, you the 20.  
> 
> Regarding 28 ref clock, that is SHM?  Why that rather than NMEA (20)?

gpsd handles a lot more GPS types than #20.  So let gpsd handle the GPS.
gpsd passes the time it determines to ntpd using the SHM (shmctl) 
interface.

The long term goal is to kill off #20 as no need to maintain 2 NMEA
parsers.

> > I use a time1 of 0.480 for my Ultimate GPS HAT.  Just about in the
> > middle of my 30 to 70 milliSec jitter.  
> 
> I don’t remember what the difference is between time1 & time2.

time1 adjusts the PPS derived time, time2 adjusts the NMEA derived time.

With #28, the NMEA time is on SHM1, and PPS time on SHM2.  So
each has its own reflock line, and fudge.  Keeps from mashing things
together and losing visibility.

> What’s a good way to “tune” my NTP config?

Compare it to another ntpd server and see which has the least jitter/wander.

> What’s a good way to monitor my NTP performance?

I stare at the results of:

root at pi2:~# watch ntpq -p

Watch how you local refclock(s) compare to some others.

> Correct, 16 = 9600 & 1 = specified the NMEA sentence to get time
> from, I think...  I’ll look at upping it on my current
> configuration.  I had to limit the statements that came out, so they
> didn’t run over the second (some periodic (every 5 or 10 seconds)
> NMEA statements made it take > 1 second for a cycle).

Thus the suggestions to go up from 9600.

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