Ahhhhh I understand the PHC thing now. Is there any way to induce as many "hops" as possible then? I set a test earlier where I just looped through a switch a whole bunch of times using VLANS, but I wasn't sure if that truly counted as a "hop" I would need to check if the switch supports PTP or not.
If push comes to shove the phc2sys might work for me.
Thank you so much for the help.
-----Original Message-----
From: Luke Bigum [mailto:***@lmax.com]
Sent: Tuesday, April 25, 2017 8:40 AM
To: linuxptp-users
Subject: Re: [Linuxptp-users] ptp inducing as many hops as possible
Kyle,
I think you've misunderstood what Richard was talking about. You can't just arbitrarily set any network interface to use any PHC - the oscillator under the PHC device is physically attached to the NIC. Unless you have a multi-port network card that shares one oscillator (eg: SolarFlare 7x22), most NICs will probably have their own PHC. That's why you're getting the device mismatch error.
I've used multiple phc2sys processes in the past to sync different NICs, but this is not a true Boundary Clock. You'll be copying time up and down the Linux stack and through the system clock, so you are subject to all sorts of kernel scheduling jitter and PCI bus latency. If you just want some sort of PTP signal and don't care so much about accuracy though, you can do this.
Also regarding your question earlier about Gain Peaking, Richard was warning you about cumulative error. So if you are proposing to go:
grandmaster -> BC 1 port 1 -> BC 1 port 2 -> BC 2 port 1 -> BC 2 port 2 -> BC 3 port 1 -> BC 3 port 3
And it costs, say, +/- 10us of jitter to go between ports, by the time you get to BC3 port 3 you'll be at +/- 60us.
--
Luke Bigum
Lead Engineer
Information Systems
----- Original Message -----
From: "Mace, Kyle P." <***@gd-ms.com>
To: "Richard Cochran" <***@gmail.com>
Cc: "linuxptp-users" <linuxptp-***@lists.sourceforge.net>
Sent: Tuesday, 25 April, 2017 14:19:47
Subject: Re: [Linuxptp-users] ptp inducing as many hops as possible
Alright I am having troubles forcing the ports to use the same PHC. When I specify which PHC to use I get an error about PHC device mismatch. Is there a way to unattach the hardware clock from a specific port?
Output of error
sudo ptp4l -i eno1 -p /dev/ptp1 -m -s
ptp4l[61532.475]: selected /dev/ptp1 as PTP clock
ptp4l[61532.475]: port 1: PHC device mismatch
ptp4l[61532.476]: port 1: /dev/ptp1 requested, but /dev/ptp0 attached
ptp4l[61532.476]: failed to open port eno1
Or would I be able to enable the boundary_clock_jbod option in a config file and then sync the clocks off the system clock using phc2sys?
-----Original Message-----
From: Richard Cochran [mailto:***@gmail.com]
Sent: Thursday, April 20, 2017 4:27 PM
To: Mace, Kyle P.
Cc: linuxptp-***@lists.sourceforge.net
Subject: Re: [Linuxptp-users] ptp inducing as many hops as possible
Post by Mace, Kyle P.I am in need to test ptp with as many 'hops' as possible. I have
multiple systems with dual Ethernet ports. I would like to have a
setup something like this: grandmaster -> BC 1 port 1 -> BC 1 port 2
-> BC 2 port 1 -> BC 2 port 2 -> BC 3 port 1 -> BC 3 port 3 ->
etc.. Anyone have any ideas if this is possible?
The linuxptp stack supports this.
Remember that all the ports of the BC must share the same clock (that is, the same PHC).
Also, long chains of BC are prone to "gain peaking".
HTH,
Richard
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