Hi people, I've been out for a while due to a bad flue and now I'm picking where I left off so...
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. 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. 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? Regards, Nico. -----Original Message----- From: Miroslav Lichvar [mailto:[email protected]] Sent: dinsdag 29 maart 2016 15:54 To: Nico Augustijn <[email protected]> Cc: [email protected] Subject: Re: [Linuxptp-devel] An update to or a new PI(D) servo? On Tue, Mar 29, 2016 at 02:44:26PM +0200, Nico Augustijn wrote: > Last week, we've upgraded the RTL of the board to use a 10 Gb MAC and found > that it introduced a fair amount of jitter on the PPS of the system compared > with 1Gb. > We believe this could be mitigated by introducing a second, "slower", set of > PI parameters that would kick in when your locking distance becomes within a > certain amount of ns (say about 70 ns, but should be configurable). Automatic switching between different sets of PI parameters could be useful and there have been some proposals to do that, but it's not clear to me how exactly you want to select the best set of parameters. If you know the second set of PI parameters performs better, why not use them right from the start? If this is about faster convergence, maybe it would be better to add the derivative term to the current servo? Also, linuxptp already has an adaptive servo, linreg. Have you tried it? -- Miroslav Lichvar ------------------------------------------------------------------------------ _______________________________________________ Linuxptp-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
