[ntp:questions] ARRGH!!! I woke up to a 50 SECOND clock error.

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Tue Mar 13 18:30:11 UTC 2012

On 3/13/2012 2:04 PM, David J Taylor wrote:
>> Hi all,
>> I just woke up to a 50 SECOND clock error.  Prior to the error, with 
>> my PC locked into the GPS and the internet servers noselected, here's 
>> what my peerstats looked like.  Baseline is the GPS.  Colored lines 
>> are internet servers.
> []
>> My system is Windows 7, NTP 4.2.7p259, GPS GlobalSat BU-353 USB NMEA 
>> only with GPGGA sentence at 57,600 baud.
>> If anyone can shed some light on what happened, please do.  It's 
>> driving me bonkers.  I don't believe the GPS is at fault, and I 
>> suspect NTPD.
>> Thanks in advance.
>> Sincerely,
>> Ron
> As all the Internet servers agreed (in another graph you showed me), I 
> would suggest that you stick with the Internet servers and discard 
> that GPS!  I hope it will be better with the PPS from the Sure board.  
> At least remove the noselect from the Internet servers so that NTP can 
> do its job properly.  At the moment you are telling NTP to trust the 
> GPS no matter what it says.  Can't think that sounds the wisest 
> option.  I might be inclined to add noselect to the GPS and measure it 
> against the Internet servers.....
> Cheers,
> David

The question is, what reset my clock abruptly 50 seconds off at around 
0637 UTC.  My loopstats file shows that the GPS was humming along quite 
nicely at that point with no anomalies at all.  I don't believe it's the 
cause of the problem.  It looks like NTPD abruptly decided to step my 
clock 50 seconds, for reasons unknown.  As far as I know, NTPD is the 
only thing active on the system that will alter the clock.  The Windows 
internet time function is disabled.  The noselects are there for testing 
only.  I won't keep them there permanently.  I'm trying to determine 
where these anomalous readings are coming from.




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Ron Frazier
timekeepingdude AT c3energy.com

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