[ntp:questions] Re: HowTo calibrate system clock frequency using NTP

David L. Mills mills at udel.edu
Thu Feb 2 19:16:37 UTC 2006


Wolfgang,

You might be missing an opportunity.

I have several times defended ntpd as a valuable diagnostic tool in that 
it directly measures the frequency and indirectly measures the 
environmental temperature. Use it to detect failed A/C or machine fans, 
even fires in the machine room. Use it to detect a Halon release without 
endangering macnine room staff. Use it as a fingerprint for each 
particular CPU; it might be useful in spam source identification. Of 
course, we all use it to detect network and server outtages. Who needs 
the time? We have a quite sensitive network sounding and reporting tool.

Dave

Wolfgang S. Rupprecht wrote:
> "Richard B. Gilbert" <rgilbert88 at comcast.net> writes:
> 
>>If you want to make a one-time correction to your clock frequency, 500
>>ms/day may be a reasonable objective.   As Terje pointed out, the
>>frequency varies with temperature and the temperature varies with the
>>time of day, season of the year, whether the heat is on or off, etc.
>>The frequency will also change, slowly, as the crystal ages.
> 
> 
> Modern motherboards all seem to have the ability to read the ambient
> temperature.  It might be possible to null out some of the temperature
> variation of the xtal by generating a table of ppm-offset vs. reported
> temperature while ntpd is running.  Then when the system runs open
> loop at some later time, some fairly simple hack can load different
> ppm corrections depending on the reported temperature.
> 
> -wolfgang




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