On Mon, Apr 23, 2018 at 07:20:25PM +0000, Cliff Spradlin via Linuxptp-users wrote: > Configuration thoughts: > - It seems to me that ptp4l should only examine the time offset between the > master and slave, and not try to estimate or correct for differences in > frequency. I couldn't find a setting for this, and it seems like frequency > estimation is baked pretty deeply into the existing control algorithms.
ptp4l can be configured to use the nullf servo. It doesn't change the frequency and can correct the clock only by stepping (if allowed by the *step_threshold options). This assumes the measured offset is consistenly below one nanosecond. I have a pair of directly connected X550 cards, which behave a bit like SyncE with the frequency. Their clocks seem to be locked to each other or some other common source. I'm not sure how this works and I'd love to see some explanation. However, in this case the measured offset is larger than 1ns and the nullf servo is constantly stepping or trying to step the clock. The PI servo configured with a very small I constant is a better choice here. It just takes longer to start. I guess a new option could be added to turn it into a pure "P" servo. -- 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
