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

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