On Fri, Apr 08, 2016 at 11:04:16AM +0200, Nico Augustijn wrote: > The selection of the parameters would be based on the "perceived locking > distance". This could be a user-settable threshold. For instance, in our > particular situation we'd want to switch to much "slower" parameters when > we're within about 100 - 200 ns of lock to reduce jitter. The reason we use > more aggressive PI values at first is that we need to be within 1 microsecond > of lock distance within 5 seconds of starting the BMCA. This is a requirement > of the SMPTE205g spec that we cannot change.
Ok, that makes sense. I'd suggest to implement this as a new "multi-stage" PI servo, independently from the PI servo that linuxptp currently has as it will probably require a carefully configuration to get good results and prevent thrashing between the two sets of constants, etc. An extra set of PI constants and a threshold wouldn't fit the configuration of the current PI servo very well. > The colleague who selected the PI servo and determined optimum parameters > tells me the linreg servo performance was not as good as the tuned PI servo. What constants the tuned PI servo used and what difference in the performance did you see? > I am not sure what you mean with "maybe it would be better to add the > derivative term to the current servo". Could you expand a bit on that? If the servo had a derivative term, I think it could converge faster as it would predict the future offset. I'm not sure if it would be as fast as the multi-stage servo you propose. In any case, extending the configuration of the current PI servo with a D term would be difficult. -- Miroslav Lichvar ------------------------------------------------------------------------------ _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
