[ntp:questions] ntpd frequency calculation

oye ogun oye_17 at yahoo.com
Thu Aug 4 11:26:55 UTC 2005

i am working on a project where i want to use ntpd to
automatically recalibrate the output of a frequency
oscillator, so as to maintain a stable output
frequency. on this project the time is really not an
issue (except to confirm that ntpd is working
properly). the whole picture is to achieve frequency
synchronization of various frequency sources
(oscillators) distributed over a network. 

the original design was to compare the difference
between ntpd time and the local oscillator time ( via
counters etc) and apply a correcting voltage to the
voltage controlled oscillator. however, as ntpd is
capable of calculating the offset of the oscillator so
that it could use this valve each time it starts
up,(to adjust the frequency), why introduce additional
latencies in operation by adding external circuits.
why not use the calculated valve to recalibrate the
oscilator at the required time periodically). if i
leave ntpd running it will continuously update the
driftfile. i dont want this to happen as a different
valve will change the tuning value.i want to maintain
a value.

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. 

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

> At 3:09 PM -0700 2005-08-03, oye ogun wrote:
> >  i have written a script to start and end ntpd and
> i
> >  used cron to shedule how often i want it done.
> 	I'm confused.  Why would you want to
> programmatically stop and 
> start ntpd, and why would you want that in cron?
> 	I can understand starting ntpd as soon as the
> machine is running, 
> and stopping it during the shutdown process, and
> even monitoring it 
> to see if it's running correctly so that it can be
> restarted if 
> necessary.
> 	But I'm having a real hard time understading why
> you would want 
> to do what you've described.
> >                                            could
> >  someone please informed me of a link that gives
> >  details calculation on how ntpd calculates the
> >  frequency offset.
> 	Why not just let ntpd calculate that value and
> store it in the file?
> -- 
> 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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