Re: [chrony-users] Accurately measuring clock drift

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Well, it is not merely a timeserver that I am after...  those are easy to find (also as surplus).
And here at home I have a LeoNTP.  Nice timeserver, unfortunately IPv4 only despite lots of promises.

We do operate a number of transmitter stations in a simulcast repeater network.
For that to work, the time on the server itself must be accurate to a few microseconds.
The original poster of this topic (that I sort of hi-jacked) seems to be doing a similar thing.

For time on the server to be that accurate, sync to another server using NTP, even over the local
network, is not good enough.  That is why we sync to 1PPS pulses from a suitable GPSDO that
also outputs the 10 MHz reference frequency for the transmitter.

We use the "1PPS to RS232 DCD input" method, with "ldattach" to make the serial port into
a /dev/pps0 and lock chrony to that.  That works reasonably well, but with many GPSDO units
that we use we need to stretch the pulse, and also the pulses are usually filtered on the
RS232 board so I think it would be better to have a dedicated board for this purpose that
solves all issues.  Maybe an Intel I210 card is closer to what we need than an RS232 port.
(still requiring the pulse stretcher / level conversion)


On 6/21/23 14:22, Joe Smith wrote:
It's been a while since I've messed with this but in a past life I created a dedicated time server using a BeagleBone/BeagleBoard SBC with a Adafruit GPS Breakout board. Runs Ubuntu and and other Linux flavors. The BeagleBone is about the size of a credit card. Put a small enclosure around it and voila! a compact time server running chrony. You can ssh into it like any other network connected Linux host to configure or maintain it. We were able to get very good time sync from this.

In one instance, my prototype was modified by someone else to use a different GPS board that had a very narrow pulse, too narrow for the BeagleBone to detect. Pulse width on the board was adjustable via cmd-line over serial cable so we just adjusted it to the same width as the Adafriut (1ms I think?).

Perhaps something along these lines might work for you. BeagleBone is about $50 and a bit more for breakout board, cables, etc. Probably around $150 or so total parts investment. I've seen people do it with Raspberry PI as well so that may be an option for you. Takes a bit of time and patience to put together but a very affordable solution. I don't have notes on the setup anymore but there was an abundance of info online and the chrony-users group is extremely helpful getting past some of the rough spots.

Hope this helps

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