Re: [chrony-users] Accurately measuring clock drift

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.

From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
Sent: Wednesday, June 21, 2023 7:53 AM
To: chrony-users@xxxxxxxxxxxxxxxxxxxx <chrony-users@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [chrony-users] Accurately measuring clock drift

On Wed, Jun 21, 2023 at 01:17:10PM +0200, Rob Janssen wrote:
> Miroslav,
>
> Are you aware of any affordable PCIe card that supports PPS input on a generic PC server?
>
> Ideally would be like this:
>
> - TTL input of a PPS signal with minimal pulse length all the way down to 100ns
> - some hardware time stamping method
> - supported interface to chrony
> - maybe even a serial port in addition

No, I'm not aware of any cards that would meet your requirements.

Normally I would recommend the Intel I210. It's cheap, widely
available and well supported. It has 3.3V SDPs. A voltage divider
would fix that for TTL logic. But it's not usable with short
pulses, at least not with the chronyd's way of detecting edges when
the HW timestamps both as the I210 does. It doesn't have a serial
port.

--
Miroslav Lichvar

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