[Linuxptp-devel] Clock servo design

[Wolfgang Wallner]

Hello LinuxPTP community,

I'm dealing with simluation of IEEE 1588 for my master thesis.
I've used the PTP-book by Eidson and the source code of LinuxPTP to get
an understanding of how a PTP implementation works.
Thanks for sharing LinuxPTP as an open source project, it was really
helpful for me :)

I would now like to design a clock servo for my PTP simulation.
I have read some papers on that topic, and again had a look on your
source code.

What where the design decisions for your implementation? Is there some
online documentation on how you have come to what is currently implemented?

When using LinuxPTP, how would one choose the values for scale and
exponent for KI and KP?

regards,
Wolfgang Wallner

[Richard Cochran]

Post by Wolfgang Wallner
What where the design decisions for your implementation? Is there some
online documentation on how you have come to what is currently implemented?

I am sorry to say that there is not really any design documentation
for the servo. The PI controller is a standard method, and the Eidson
book covers it pretty well, I think.

The only really clever bit is the automatic parameter scaling that
Miroslav invented. There was a bit on discussion about that on the
list. He used a simulation approach to find appropriate values.

Post by Wolfgang Wallner
When using LinuxPTP, how would one choose the values for scale and
exponent for KI and KP?

It really depends on your needs.

I think the defaults are fine for most purposes. I am not a control
theory expert, but my understanding is that for PI controllers, one
usually looks at the step response (like in Eidson) and also the
frequency behavior (Bode plot and the like).

Using Miroslav's simulation tools you can experiment with various
alternatives, and you don't have to wait long to get your results.

Thanks,
Richard