Chrony on CM4

On Mon, Aug 21, 2023 at 3:28 PM Miroslav Lichvar <[email protected]> wrote:

> As for the PTP-specific timestamping of the CM4 NIC, I'm interested in
> tests using the NTP-over-PTP transport with the latest chrony version
> (you might need to set hwtstimeout to 0.1 or even longer for the CM4).

I've written a guide to how to set Fedora and chrony on the CM4 so as
to take advantage of both NTP-over-PTP and PHC extpps:

https://github.com/jclark/rpi-cm4-ptp-guide/blob/main/fedora.md
https://github.com/jclark/rpi-cm4-ptp-guide/blob/main/chrony.md

Corrections/suggestions welcome.

I'm using the CM4 as a server (with a very inexpensive GPS). As a
client, I used a PC with an AQC107 10GbE card (using atlantic driver),
also running Fedora (the AQC107 is cheapest 10Gbe card around, and can
only timestamp PTP packets). There are two switches in between.

It seems to be working properly: I get no errors and much better
results than with another local chrony server that is not using
hardware timestamping. But how do I tell if the hardware timestamping
is working properly in both directions?

I haven't tried to optimize it yet. The RMS offset on the client seems
to jump around more than I would expect: sometimes around 1us;
sometimes down to a few hundred nanoseconds. Not sure if that is the
switches or the CM4 flakiness or less than optimal configuration.

What would be good tests/measurements to do?

James

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