Proposal - drop the GPSD JSON driver

Gary E. Miller gem at
Thu Oct 20 21:39:13 UTC 2016

Yo Hal!

On Thu, 20 Oct 2016 14:19:05 -0700
Hal Murray <hmurray at> wrote:

> esr at said:
> >> 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.   
> We can test it with the current code.  Just setup ntpd to use both
> SHM and JSON.

Been there, done that, when Pearly wrote the GPSD JSON driver.  Except
for all the bugs in his driver, there is zero perfomance difference.

And that makes logical sense, the deltas are from KPPS, and they are
unused by ntpd for up to (default) 64 seconds), then averaged.  So even
a few seconds of delay is irrelevant.

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