[ntp:hackers] GPSD client clock & latency issues

Gary E. Miller gem at rellim.com
Wed Feb 19 23:11:26 UTC 2014


Yo juergen!

On Wed, 19 Feb 2014 19:14:25 +0100
juergen perlinger <juergen.perlinger at t-online.de> wrote:

> But since I have no numbers I have measured on my own, I might stand
> corrected. If we find that the GPSD protocol limits the precision, we
> should talk to the GPSD people ASAP. Since I have a only a GPS18xLVC,
> which has only 1usec precision, I will have some trouble when
> attempting to get better than that.

If you use a recent gpsd with a recent ntpd, then you will get nSec
resolution.  The accuracy of the GPS18xLVC is 1 uSec which is also the
timer resolution in older gpsd.  If you use the new nSec resolution you
will see the short term jitter of the GPS18xLVC drop from about 1.5
uSec to about 700 nSec, as measured by ntpq.  This is a simple Nyquist
sampling effect.



RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
	gem at rellim.com  Tel:+1(541)382-8588
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