On Tue, Feb 14, 2017 at 04:33:34PM +0000, Urs Ritzmann wrote: > I know, moving time from the less accurate, higher jitter NTP domain to the > PTP domain is a bad idea in general, but the use case is still valid. And it > seems to be possible, given a filter with slow enough time constant to remove > most of the NTP and Software timestamping jitter. > > Currently, I created an additional servo class, which is basically an > exponential smoothing / low-pass filter with a gain constant. If you think it > could be useful for others, I would probably change the code a little before > sending patches. Instead of the servo class, I think this matches the current > implementation better: > > - Use the PI-Servo, but change it to accept zero integral constants, > optionally making it a P-Servo. Integral part reduces stability margin and is > not required if some remaining static error is acceptable (which is in my > case). > - Add an option to phc2sys to enable timestamp filtering (disabled by > default). > - Use the already existing moving average filter or alternatively add a new > exponential smoothing filter class to the filters.
In general this looks interesting, but it's not very clear to me what would be the advantage over using the PI servo with smaller constants. Have you tried constants like -P 1e-4 -I 1e-8? If the system clock is accurate and stable to a millisecond, this should keep the PHC accurate to few milliseconds and stable to hundreds of nanoseconds, assuming the PHC is in a reasonably stable temperature. -- 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-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
