[ntp:questions] how do I lock in average frequency correction

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Sun Feb 12 03:39:58 UTC 2012

Hi all,

I've been reading around in the faq's at ntp.org and various pages 
googling around and cannot find obvious answers to these questions.

It is my understanding that NTP is continuously making small changes to 
the software clock to keep the timing accurate while the os is running.  
95% of the time, my computers are doing the same thing and 95% of the 
time, I'm doing the same thing with the computers.  Therefore, over a 
long time interval, the interrupt usage should be similar, and over a 
long time interval, the correct clock frequency to maintain accuracy 
should be similar.

So, what I want to do is figure out what the average frequency to keep 
accurate time is over say a week or month.  I then want to fix the 
frequency at that level and leave it there.  Then, under normal 
conditions, the clock should drift very little on average.  If certain 
usage conditions, say transcoding a movie, make the clock drift more 
rapidly, I want it to step the time or slew it for that occasion, but 
not to alter the long term correction factor at all.  That way, when my 
usage patterns return to normal, the drift should again return to a very 
slow rate.

I also would like to understand how ntp interacts with the Real Time 
Clock.  I think I've read that either NTP or the OS (I don't know which) 
will save the time to the RTC when shutting down and retrieve the time 
from the RTC when booting up.  I'd like to know if this is true, first 
of all, and I'd like to know if it makes any corrections to the clock 
rate of the RTC so it is more accurate.

Any help is appreciated.



(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
such.  I don't always see new messages very quickly.  If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)

Ron Frazier
timekeepingdude AT c3energy.com

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