Re: [Linuxptp-users] Grandmaster Auto-Negotiation and Reconfiguration of phc2sys to ptp4l Synchronization

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

On Mon, Aug 17, 2015 at 02:14:36PM +0000, Harold Lapprich wrote:
> 	"If you run ptp4l on all your systems, and each one also running phc2sys, it will:
> 
> 	on system which is "master"
> 
> 		phc2sys will drive the ptp4l hw clock based on local time
> 
> 		ptp4l will sync time out the network using PTP
> 
> 	on systems which are not master
> 
> 		ptp4l will sync time in from network to hw clock
> 
> 		phc2sys will sync hw clock to CLOCK_REALTIME.
> 
> 	But if you want to also use NTP as a clock source, then you need to use timemaster, as otherwise phc2sys and ntpd will interfere with each other."

Strictly speaking you just need to configure phc2sys to use the NTP
SHM servo to feed chronyd/ntpd so they can select the best source or
combine multiple sources and synchronize the clock. That's how phc2sys
is configured by timemaster.

Do you need NTP as a time source? Or just serve time over NTP? The
former conflicts with your requirement to allow ptp4l to be a master
as phc2sys would need to be the process that synchronizes the clock
and not chronyd/ntpd.

If you just need to serve NTP, you can configure chronyd/ntpd to not
synchronize the clock and keep phc2sys in the control of the clock.

> So when NTP is to be the clock source (and vice versa)  then 'timermaster' is needed because phc2sys and ntpd will interfere with one another. Now the problem is GrandMaster failure, if I understand you correctly when another PTP system on the network becomes the GrandMater 'timemaster' will NOT automatically reconfigure and start using NTP as the clock source (using timemaster to start PTP configuration on all systems on the PTP network)?

The problem is that when phc2sys is configured to feed chronyd/ntpd,
it is not able to synchronize the PTP clock in the reverse direction
when ptp4l is master.

> If this is the case then one would have to have another application running in the background to detect the switch, create the appropriate 'timemaster' configuration file and start?

There is currently no way to configure timemaster to serve local time
over PTP. phc2sys would need to allow that first.

-- 
Miroslav Lichvar