[ntp:questions] ntp ports

Terje Mathisen terje.mathisen at hda.hydro.com
Mon Nov 10 20:47:58 UTC 2008

Hal Murray wrote:
>> I have three inhouse GPS receivers, in three separate cities. Each city 
>> has two FreeBSD-based ntp servers, one of which is currently connected 
>> to the local GPS, but the other is pre-configured so that in case of a 
>> primary server crash, the serial cable can be moved over.
> What sort of GPS units are you using?

These are the integrated Oncore 12-channel timing receivers, phk had an 
array of them on his shack at one point:


> Many of them talk without asking once you get them setup correctly.
> You can run those through a line buffer/splitter and drive several
> ntp servers at the same time.

The Oncore receivers require a polling command to be sent every second, 
so in theory you could do it by only connecting the TX line from one of 
the servers, but this would only work if the servers were perfectly in 
sync, since the driver goes through several initialization stages on 

Connecting just the PPS signal would have worked, but it really doesn't 

It is more important that I also have a few more unofficial S1 servers, 
in the form of a home-made Garmin 18, a US-based CDMA cellphone unit, 
three black box units (three models from two different vendors).

My DFC-77 clock in Germany is unfortunately not in operation. :-(


- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"

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