[ntp:questions] Sure serial - USB with PPS performs 16% better after Windows reboot

Chris Albertson albertson.chris at gmail.com
Sun Mar 25 21:23:52 UTC 2012


Yes, I see the graph has segments.

I'm guessing that NTP's clock selection process switched the set of
Internet servers it was using.  Would be easy to check the log.

"offset" of course is the difference between two clocks.  My guess is
that the GPS is stable and it's the Internet that is moving.

At some point as you go much below 1mS error you will need some other
reference in order to sort out if the error is in NTP, GPS or your
Internet connection.

On Sun, Mar 25, 2012 at 1:51 PM, Ron Frazier (NTP)
<timekeepingntplist at c3energy.com> wrote:
> Hi all,
> I think I've discovered something very interesting.  Just by chance, I had
> to take the laptop computer to someone else's house the other day to do some
> work.  So, I shut it down and unplugged the GPS and left.  When I came back,
> I plugged the GPS back in and rebooted.  After a while, I checked my graphs.
>  I found peak offsets in the 800 us range rather than in the 1.2 ms range I
> had seen before.  I restarted NTPD and started another graph.  After a
> while,  saw the 1.2 ms offsets I had seen in the past.  Then, after forming
> a theory that the reboot may have some effect.  I rebooted again.  After
> letting the graph run a while, I was again seeing offsets in the 800 us
> range.  See the graph below.
> http://dl.dropbox.com/u/9879631/2012-03-24-2327-loopstats-reboot-restart-reboot.png
> There are three distinct sections.  First, is the beginning.  Here, as you
> can see, the peak offsets are approximately + .8 / - .6 ms.  Then, there is
> the middle.  As you can see, peak offsets are approximately + 1.2 / - 1.2
> ms.  Then, there is the end.  There are two subsections here.  In the first,
> the peak offsets are approximately + .8 / - .6 ms again.  In the second
> subsection, the peak offsets are approximately + 1 / - .7 ms.  I don't know
> why there is a variance between the subsections.  However, the beginning of
> the graph is a time just after a reboot, the middle is a time just after an
> NTPD restart, and the end is a time just after another reboot.
> I can use the signal either way.  I just thought this was interesting.
>  Anybody know what's going on?
> Sincerely,
> Ron
> --
> (PS - If you email me and don't get a quick response, don't be concerned.
> I get about 300 emails per day from alternate energy mailing lists and
> such.  I don't always see new messages very quickly.  If you need a
> reply and have not heard from me in 1 - 2 weeks, send your message again.)
> Ron Frazier
> timekeepingdude AT c3energy.com
> _______________________________________________
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Chris Albertson
Redondo Beach, California

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