[ntp:questions] Synching to a Legacy System as an External Clock Reference
kostecke at ntp.isc.org
Fri May 18 02:25:53 UTC 2007
On 2007-05-18, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
> michael.antinucci at lmco.com wrote:
>> I have an old legacy external system that I need to synchronize with
>> that sends custom protocol UDP packets containing a single field in
>> the packet that contains the legacy system's current clock time (in
> Since your internal systems are already synchronized using NTP, it
> should be fairly trivial to install ntpd on the external system and
> get it synchronized too.
Not if that old legacy system isn't an architecture that ntpd has been
>> The current clock time starts at 0 when the system boots and
>> increments forever thereafter. The frequency of this message is at
>> least every 10 seconds, not 1 PPS like I would like.
>> My hope is to have my internal system's NTP server receive the 10
>> second clock pulses from the old legacy system over UDP and have my
>> internal system's NTP server synchronize with it.
Use a daemon that listens to the UDP clock pulses and, after suitable
preprocessing, sends them to ntpd via the SHM driver.
>> I read this fine article (which I think is the path to take) but I
>> need a clearer explanation on what to do.
> I think that, in the article you refer to, Dr. Mills is referring to a
> system or a hardware clock that actually knows what time it is!
The stability of the time base is of primary importance. Numbering the
seconds is trivial in comparison.
> Your external system has no clue what time it is as we understand it.
> It just ticks periodically and the period is apparently "approximately
> ten seconds"
Actually, it sends a packet containing the clock counter (ostensibly
milliseconds since system startup) approximately every ten seconds.
That's not the same thing as "just tick[ing] periodically".
Steve Kostecke <kostecke at ntp.isc.org>
NTP Public Services Project - http://ntp.isc.org/
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