[time-nuts] Tracking NTP displacement and correlation betweentwo clients.

David davidwhess at gmail.com
Fri Oct 5 05:34:20 UTC 2012


I had an early Phenom II that lost time while turned on but the
internal CMOS clock did not so rebooting or reading the CMOS clock
restored the correct time.  There was a problem with the System
Management Mode code and The C1E CPU state which was new at that time
where an interrupt was being lost.  Disabling the low power CPU state
fixed it until a BIOS update was released.

It has been a while but as I recall, the NTP client kept the OS from
drifting further behind but the time was still noticeably off.

On Fri, 5 Oct 2012 00:42:42 -0400, Bob Bownes <bownes at gmail.com>
wrote:

>David,
>
>The problem is that they start in sync and over the course of a day drift that far apart despite having NTP running. We're not sure why NTP isn't correcting it along the way. Though at this point, we are looking at a firmware bug.
>
>Thanks!
>Bob
>
>On Oct 5, 2012, at 12:30 AM, "David J Taylor" <david-taylor at blueyonder.co.uk> wrote:
>
>> The problem stems from one of the two (identical) machines drifting off by
>> 60-70 seconds per day. So a few ms here and there are ok.
>> []
>> Bob
>> ==================================
>> 
>> Bob,
>> 
>> NTP is normally limited to a +/- 500 parts per million correction - 43 seconds per day.  You may be operating outside the range NTP is expecting to handle.  If the clock offset is a stable value of 60-70 seconds per day you can bias NTP to correct within +/- 500 ppm of that drift.
>> 
>> Cheers,
>> David
>> -- 
>> SatSignal Software - Quality software written to your requirements
>> Web: http://www.satsignal.eu
>> Email: david-taylor at blueyonder.co.uk 
>> 
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