Proposal - drop the GPSD JSON driver

Gary E. Miller gem at
Thu Oct 20 21:36:24 UTC 2016

Yo Eric!

On Thu, 20 Oct 2016 16:52:06 -0400
"Eric S. Raymond" <esr at> wrote:

> > The SHM interface is deltas.  gpsd figures out the offset and sends
> > that over to ntpd.  How gpsd figures out that offset has nothing to
> > do with SHM or JSON or anything else involved with getting the data
> > to ntpd.  The offset won't change much in a short time so modest
> > latency doesn't matter.  
> Your last sentence is one of the assumptions we're now questioning.
> I didn't question it before either, which is why the above hack is
> not implemented.

Ony you are questioning it.  Deltas have been around in ntpd for
decades.  Then they get averaged over minpoll, which default to 64
seconds!  The jitter you are looking for is not there.

> As you say, we need to try several methods and measure.

Try all you want, but the deltas come from KPPS, and the 64 second
averaging is in the core ntpd.  How they hook up is, by design, not
a factor in performance.

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