| Re: [chrony-users] PHC / NIC / PPS mismatch |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] PHC / NIC / PPS mismatch
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Wed, 1 Dec 2021 08:58:00 +0100
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On Tue, Nov 30, 2021 at 09:29:18PM -0800, Christopher Hoover wrote:
> i210/i211 won't timestamp extpps unless the interface is up.
Thanks for the information. I think I hit that too at some point.
> (I'm still not sure why I was sometimes seeing a 1 Hz ticker -- I
> suspect that is some free running clock in the NIC being counted at 1
> Hz.)
Maybe it was the virtual PPS generated by the NIC and timestamped by
the system clock using interrupts (i.e. not great for synchronization),
presented as /dev/pps*.
The i210 can also generate PPS on one of its SDPs and it can be looped
back to other SDP. This can be useful for testing if you don't have an
external PPS. One problem with the generated PPS is that it randomly
selects the rising and falling edge, so you might need to restart it
couple times if you are feeding something that timestamps only one of
the edges (the i210 timestamps both).
--
Miroslav Lichvar
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