Re: [Linuxptp-devel] Optimal P, I constants

[Keller, J. E <jac...@in...>]

> -----Original Message-----
> From: Richard Cochran [mailto:ric...@gm...]
> Sent: Wednesday, April 24, 2013 11:52 AM
> To: Miroslav Lichvar
> Cc: lin...@li...
> Subject: Re: [Linuxptp-devel] Optimal P, I constants
> 
> On Tue, Apr 23, 2013 at 03:45:12PM +0200, Miroslav Lichvar wrote:
> 
> > This one is with 100us jitter, 10ppb/s wander and 1s interval. The
> > best I constant now becomes impractical as it will take hours
> > for the servo to converge.
> 
> What clock has 100us jitter? Are you trying to model time stamp error,
> like in SW time stamping?
> 
> > I was wondering how useful it would be to have a new servo
> parameter
> > for the Allan intercept and set the P, I constants automatically
> > according the intercept and measured clock update interval. What do
> > you think?
> 
> I would like to have a table of PI constants, with one pair for each
> (reasonable) sync rate. I don't think these need to be tuned to
> particular oscillator characteristics, but rather just for "typical"
> hardware. Most people will not know what they have and will not be
> able to measure the Allan deviation of their clock.
> 
> Your simulation results are interesting. Do you propose to find PI
> values for different sync rates in this way?
> 
> Thanks,
> Richard
> 

How difficult would it be to calculate allan deviation on the fly? If it's  not possible, then definitely having some good P/I values per hardware would be good.

Miroslav: I would like to know how to measure these so that I can find optimal values for the hardware I support. Thanks.

- Jake