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Re: [gpsd-dev] RaspbPi HOWTO


From: Gary E. Miller
Subject: Re: [gpsd-dev] RaspbPi HOWTO
Date: Thu, 5 May 2016 10:39:40 -0700

Yo Gary!

On Thu, 5 May 2016 10:19:49 -0700
"Gary E. Miller" <address@hidden> wrote:

> I have never seen a USB GPS w/ PPS be the limiting factor, always the
> NTP over the ethernet.  I'll do a test today on a Pi2 to see if that
> continues to be true.


After shoving a bit more espresso in my face, and looking at a Pi2 that
has been runnning ntpd, no gpsd, for a few days, I get the answer that
should have been painfully obvious at first.

The NTP over the 100Base-T that goes in the USB High-Speed to the Pi,
gets 0.3 milliSec of jitter.

address@hidden:~# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+spidey.rellim.c .GPS1.           1 u  685 1024  377    0.282    0.417   0.302
*catbert.rellim. .SHM.            1 u  405 1024  377    0.329    1.168   0.707
+darth.inow.com  204.17.205.1     2 u  889 1024  377    0.582    0.723   0.448

That would be about 2x worse than I would expect from a High-Speed USB GPS
w/ PPS.  Better than a Full-Speed, like the GR-601W, at 0.500 milliSec.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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