Re: [Linuxptp-users] Proportional Integral clock servo

[Jason L. <ker...@gm...>]

Dear all:
After reading some past posts
(http://sourceforge.net/mailarchive/message.php?msg_id=30759331),
 I have a little realization about PI controller.

I also find some resources about PID controller:
https://controls.engin.umich.edu/wiki/index.php/Recorded_Lectures

And definition of synchronization (Frequency synchronization and Time
synchronization):
http://huawei.com/ilink/cnenterprise/download/HW_194944

There are three states in clock_synchronize(), clock.c,
namely SERVO_UNLOCKED, SERVO_JUMP, and SERVO_LOCKED.

I think SERVO_JUMP state does time synchronization,
and SERVO_LOCKED state does frequency synchronization.

The ideal condition is that if the frequency of master clock and ordinary
clock is the same,
after doing time synchronization, the following "c->master_offset" is zero.

So, can we evaluate the performance of PI controller
by calculating the averages (closer to zero) or standard deviation of
"c->master_offset" in a period?

Does it make sense?

But, it is best to evaluate the pulse per second, if hw-supported.

F.Y.I.
Thanks.

Jason.


2013/7/26 Keller, Jacob E <jac...@in...>

> On Thu, 2013-07-25 at 14:55 +0800, Jason Lin wrote:
> > Dear all:
> > I am confused about the value of HWTS_KP, HWTS_KI, SWTS_KP,
> > and SWTS_KI.
> > How are these values decided?
> >
> >
> > Any recommended resources about proportional integral?
> >
> >
> > Thanks.
> > Jason.
> >
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>
> The values are set by the configuration files, and the defaults may be
> good for you. Miroslav and Richard know a bit more about how the values
> are determined. If I recall, we currently generate these values from
> other settings based on the PTP sync rate.
>
> There are some good resources in the mailing list history via discussion
> about servos between Miroslav and Richard that you might try to find.
>
> I don't have any particularly good resources I could link to you
> though.. Clock discipline is somewhat complex.
>
> The HWTS_KP and HWTS_KI are for hardware timestamping modes, where as
> the SWTS_KP and SWTS_KI values are used when we are in software
> timestamping mode. Software timestamping is done in the driver just
> before handing the data to be transmitted. Hardware timestamping is done
> either in the PHY or in the MAC (depends on what type of hardware).
> Either type requires that the driver supports it.
>
> The software timestamp constants are different because software
> timestamping has higher latency and so requires different values to
> converge in a smooth and stable manner.
>
> - Jake
>