[ntp:questions] Sure serial - USB with PPS performs 16% better after Windows reboot
Ron Frazier (NTP)
timekeepingntplist at c3energy.com
Sun Mar 25 22:14:12 UTC 2012
I see what you're saying. However, all the internet servers are
currently noselected. So, everything on this graph represents NTPD
polling the serial GPS through the serial - USB converter.
I'm not particularly worried about it. I was just wondering why the
system would apparently perform better after a reboot than after an NTPD
restart.
Ron
On 3/25/2012 5:23 PM, Chris Albertson wrote:
> Ron,
>
> 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
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Ron Frazier
timekeepingdude AT c3energy.com
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