[ntp:questions] ntpd frequency calculation

Brad Knowles brad at stop.mail-abuse.org
Thu Aug 4 11:39:45 UTC 2005

At 4:26 AM -0700 2005-08-04, oye ogun wrote:

>  the drift pattern of most VCO can be obtained from the
>  data sheet and from free run. i want to study how ntpd
>  calculates  the frequency upset.starting and stopping
>  ntpd periodically is to try to make use of its
>  frequency correction facility and not necessary the
>  time facility.

	Well, ntpd won't even try to create the driftfile until it has 
gathered enough information over the long term, and that usually 
means at least 24 hours has to go by.  Moreover, if you look at the 
value in the driftfile over time, you will find significant 
variations due to daily temperature shifts, etc....

	There's not just one and only one value.  There's only one value 
at any one point in time, and that is written to the file, but that's 
just what ntpd has calculated so far, based on the previous value it 
had calculated plus more recent measurements.

	Given the way you're trying to abuse ntpd, it sounds to me like 
you need to do a lot more homework reading the mathematical formulas 
and algorithms that Dr. Mills has recorded in his voluminous 
documentation, and you need to spend a lot more time reading the code.

	Trying to get answers to single questions that are taken totally 
out of context is not likely to be productive.  If anything, it's 
likely to be very counter-productive, wasting your time and ours.

Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.

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