Re: [Linuxptp-users] ptp4l and SyncE

[Keller, J. E <jac...@in...>]

> -----Original Message-----
> From: Miroslav Lichvar [mailto:mli...@re...]
> Sent: Wednesday, May 02, 2018 6:46 AM
> To: Keller, Jacob E <jac...@in...>
> Cc: Cliff Spradlin <th...@go...>; lin...@li...
> Subject: Re: [Linuxptp-users] ptp4l and SyncE
> 
> On Thu, Apr 26, 2018 at 06:24:39PM +0000, Keller, Jacob E wrote:
> > In the case of two X550T cards, I would expect there to be *some* difference,
> but if the clock sources are high quality it is possible they are close enough that
> we can't detect any difference in them? (though, changing frequency in on PHC
> using the ptp API should not affect the other, unless something else is connecting
> them...)
> 
> As expected, changing the PHC frequency on one card doesn't seem to
> change the frequency on the other.
> 
> I left them running for a couple of days, both frequencies set to 0
> with phc_ctl, and logged the offset measured by ptp4l using the NTPSHM
> servo (i.e. not making any adjustments). The offset between them is
> not exactly zero, but it's actually about 0.46 ppb. It seems to be the
> same with both 1Gb and 10Gb link speeds.
> 
> Here is a plot of the Allan deviation:
> https://i.imgur.com/jp3ZE3Z.png
> 
> Unless they have a hidden chip-scale atomic clock, I think they must
> be synchronized to each other in some way. Maybe something was
> implemented in preparation for SyncE support?
> 
> --
> Miroslav Lichvar

Could be, I don't know enough about the clock setup in the X550T.

Thanks,
Jake