Re: [Linuxptp-users] Help to understand the ambiguity with phc2sys options

[Miroslav L. <mli...@re...>]

On Thu, Dec 01, 2022 at 09:36:54PM +0000, Nemo Crypto wrote:
> Hi Experts,
> 
> According to the man page of phc2sys, it is used to synchronize 2 or more clocks in the system. May I know what does this mean?

Maybe more clear would be to say it synchronizes one or more clocks to
another clock.

With some options it doesn't even have to synchronize anything.

> To my understanding, phc2sys is used to synchronize the system clock based on the phc in 2 ways, either by directly reading the phc time periodically, or using the PHC's PPS output as PPS source. So it is always for synchronizing the system clock? I do not understand why 2 or more clocks would be synchronized? Does it mean, there could be multiple system clocks and minimum no. of sys clock is 2?

There is just one system clock.

> option -a => I looked at the code, and according to this, it is "autocfg". Can someone please explain the scenario of this autocfg? 

Instead of the clocks being specified on the phc2sys command line it
asks ptp4l with what clocks it is configured.

> The manpage says - read the "clocks" to synchronize. Does it mean, there can be multiple PHC? 
> Can there be one PHC on each port of a system?

Yes, it depends on the hardware. Each port of a NIC can have its own
PHC or they can share a common PHC.

-- 
Miroslav Lichvar