Re: [Linuxptp-users] gPTP issues with ntpd

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

On Thu, Jul 21, 2022 at 02:13:29PM +0200, Jakub Raczyński wrote:
> My interpretation is based only on ntpshmmon tool - it clearly shows that ntpshm servo is only fed when PTP portState is set to Slave. So it is used only to write to the segment, but phc2sys clearly controls when it is done. Since ntpd does not communicate with phc2sys then whether it works or not is only based on phc2sys.

You said something about ntpd reset. I'm not sure what that is. If
there was something removing the segment (e.g. a script using ipcrm)
before phc2sys reverses the direction, it would create a new SHM, which
wouldn't be monitored by ntpshmmon started earlier.

> It seems you have great feature of phc2sys that allows to synchronize ntpshm servo in Slave state and use CLOCK_REALTIME as Master, yet you say like it does not exist. And again, I intend to use it that way. I am not trying to read anything from ntpshm.

ntpshm doesn't synchronize anything. It just provides data for another
process to synchronize the clock. ntpd can synchronize CLOCK_REALTIME,
but not a PHC, and even if it could, it wouldn't know when it should
switch.

You need two phc2sys instances.

-- 
Miroslav Lichvar