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 ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
