[Linuxptp-users] One PCs with multiple NICs acting as multiple PTP master / PTP chains

[Koehrer M. (ETAS/ESW5) <mat...@et...>]

Hi all,

to synchronize a couple (6-8) PCs I want to use one PCs PTP master and the others as PTP slaves.
To interconnect the PCs I can use a PTP capable switch. However these switches are fairly expensive.
The first question I have: How does a "standard" Ethernet switch perform? Which accuracy will be possible if no other traffic is running over the switch but PTP packets?

To avoid a PTP capable switch I can think of a solution to use one PC as PTP master, to plug in two 4-port NICs in this master PC and use point-to-point connections to the other PCs.
Assume the Ethernet devices to be used by the PTP master are eth1, eth2, ...eth7
it should be possible to run something like
ptp4l -p /dev/ptp1 -i eth1 &
ptp4l -p /dev/ptp2 -i eth2 &
...
ptp4l -p /dev/ptp7 -i eth7 &

Is this assumption correct?
Is it possible to set up a system like that.


A different approach could be to run something like a "chain" of point-to-point Ethernet connections:
[PC MASTER] --- (eth) --- [PC 1] --- (eth) --- [PC 2] --- (eth) --- [PC 3] --- (eth) --- [PC 4] --- ...

The first PC (PC MASTER) acts as overall time master.
It is the master on the Ethernet connection between PC Master and PC 1.
PC 1 is slave on this Ethernet and acts as a master on the Ethernet between PC 1 and PC 2.
etc.
Doing this, the accuracy decreases with each member of the chain; however the overall accuracy could be good enough.
My question is here:
How does the configuration of PC 1 ... PC 7 look like?
As PC 1 ... PC 7 have two PTP clocks running, these clocks have to be synchronized.
Is this done via phc2sys? If yes, do I have to synchronize directly from PTPx to PTPy or does it work via the PCs System clock?

Thanks for any hints or recommendations

Regards

Mathias