Re: [Linuxptp-users] Can ptp4l be used without phc2sys?

[Richard C. <ric...@gm...>]

On Mon, Aug 17, 2020 at 06:07:41PM +0000, Irene Kravets wrote:
> Can ptp4l be used without phc2sys on a PTP slave to produce a 1PPS
> signal that's synchronized to the master's 1PPS?

Yes.

> If my understanding is correct, I would expect that running just
> ptp4l would be sufficient to sync 1PPS signals, however, when I
> tried it, the 1PPS signals were not synchronized.  I thought that
> phc2sys is only needed to synchronize the system clock to PHC and
> that phc2sys should not be needed to synchronize 1PPS, but that's
> not what I am observing.  Is my understanding wrong?

No, you are correct.  The phc2sys program synchronizes the Linux
system clock from the PHC.

> When I run both ptp4l and phc2sys on the slave, the 1PPS signal is
> synchronized, but there is a 2-3 usec delay between master and slave
> 1PPS signal when I observe both on a scope.  Why is that delay there
> and is there any way to make it much smaller?  I need them to be
> within 20-30 nsec of each other.

If the PPS signal is being produced by the PHC, then the offsets
should be lower.  I guess your PPS is NOT coming from the PHC?  Well,
I can only guess, because you did not provide any information about
your hardware.

Thanks,
Richard