Raspberry Pi NTP config with fudge factors

[Gary E. Miller]

Yo Eric!

On Fri, 6 May 2016 10:01:05 -0400
"Eric S. Raymond" <esr at thyrsus.com> wrote:

> Gary E. Miller <gem at rellim.com>:
> > When you disconnect the PPS, your GPS_NMEA(0) can no longer report
> > PPS base time, so it will report the NMEA based time.  To not so
> > closely related times, mushed into one.  If you GPS stop PPS when
> > it does not have a good signal the GPS_NMEA(0) will jump wildly.
> > ntpd will mark it a false ticker and then you got shit.  
> 
> It sounds like this has implications for how I should write the HOWTO
> recipe.  Are you saying that with refclock 20 the source can get
> marked as a falseticker if it loses PPS for a while?

Yup.  Easy to test, just disconnect the PPS signal, if the #20 acts
like the #48, it will start tracking the NMEA time, which will be offset
and jittery.  When the PPS returns ntpd will rule out that clock due to
the high jitter.  Eventually it sorts itself out, as long as the GPS
stays locked.

I'm busy today, but I'll run some tests later to verify that is the
current behavior.  At a minimum #2 makes it very hhard to see the NMEA
time and fix a good offset.  

Last I looked at #48 it was bad in the default configuration due to the
same NMEA/PPS mashing.

> If that's so, then maybe we do want to base the build on refclock 28
> and what you call gpsd-lite.

With the QNX thing, I wonder how portable #28 is.  Maybe the thing to do is
fix #48 or #20.  But I fear we'll start Yack Shearing.

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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