Is it possible to achieve time synchronization through a non-TSN hub?

[jack04060201]

Hello, I'm trying to connect two devices to ls1021a-tsn, through a hub for time synchronization.

It's clear that I have failed as the clocks are not synchronized. I suspect that this might be because PTP cannot synchronize two devices simultaneously on a single port.

So, I attempted to remove one of the computers. If it's possible to synchronize them through the hub, maybe I can use two different MAC addresses to achieve synchronization. However, that also failed. Why can't I achieve one-to-one synchronization in the scenario where a hub is involved? Because I'm receiving PTP packets from the avb-bridge on the PC as usual.

[vladimiroltean]

What linuxptp configuration file are you using?

[jack04060201]

What linuxptp configuration file are you using?

Hello, this is my PTP configuration.

When using the command, avb-bridge is accompanied by the -m option, while the PC is accompanied by the -s option.

Thank you for your response.

[global]
gmCapable 1
priority1 248
priority2 248
socket_priority 7
logAnnounceInterval 0
logSyncInterval -3
syncReceiptTimeout 3
neighborPropDelayThresh 1000
min_neighbor_prop_delay -20000000
assume_two_step 1
path_trace_enabled 1
follow_up_info 1
transportSpecific 0x1
ptp_dst_mac 01:80:C2:00:00:0E
network_transport L2
delay_mechanism P2P
tx_timestamp_timeout 200
step_threshold 0.00002

[vladimiroltean]

Increase neighborPropDelayThresh to a value higher than 1000 (ns == 1 us). A hub will increase the link delay which will cause the gPTP protocol to detect that the PTP link partners aren't directly connected and to fail. IOW, it fails by design, but you can still hack it if you want to. Nothing to do with having different MAC addresses.

[jack04060201]

Increase neighborPropDelayThresh to a value higher than 1000 (ns == 1 us). A hub will increase the link delay which will cause the gPTP protocol to detect that the PTP link partners aren't directly connected and to fail. IOW, it fails by design, but you can still hack it if you want to. Nothing to do with having different MAC addresses.

Hello, I successfully synchronized one of the PCs by making modifications. Thank you for your assistance.

However, I need to synchronize both computers simultaneously. When I mentioned different MAC addresses, I was referring to enabling two different PTP programs and using different ptp_dst_mac to synchronize the same computer. Is it possible to use ptp4l to synchronize both of them in the original scenario?

[vladimiroltean]

01:80:C2:00:00:0E is a multicast MAC address. Use your favorite search engine to find out what that means. You don't need separate ptp4l processes on the GM for multiple slaves.

[jack04060201]

01:80:C2:00:00:0E is a multicast MAC address. Use your favorite search engine to find out what that means. You don't need separate ptp4l processes on the GM for multiple slaves.

Yes, I understand that ptp4l uses multicast for synchronization. However, even though I used the -s option on both PCs, I still encountered multiple peer responses and rogue peer delays. That's why I suspect that it may not work properly with multiple devices. I am currently researching this issue.

[vladimiroltean]

Multiple peer responses are expected, since there are truly multiple PTP peers on the same Ethernet segment, thanks to the hub. Use "delay_mechanism E2E" instead of P2P.

[jack04060201]

When I use E2E, I don't receive any packets from the bridge, and all endpoints are in the "selected local clock as best master" state.

[vladimiroltean]

Yes, I'm afraid you'll have to remove the LS1021A-TSN switch from the path, or use PTP over IP on the endpoints to bypass its PTP packet processing. You can't combine technologies quite so freely.

[jack04060201]

Yes, I'm afraid you'll have to remove the LS1021A-TSN switch from the path, or use PTP over IP on the endpoints to bypass its PTP packet processing. You can't combine technologies quite so freely.

Unfortunately, ls1021a-tsn is the backbone of my network and cannot be removed. So, I am trying to bypass this limitation by using two PTP programs. Strangely, even though I changed the ptp_dst_mac setting on one of the PCs, it still seems to be affected by packets with the destination MAC address 01:80:c2:00:00:0e, resulting in multiple peer responses. Do you think it is possible to achieve this, or is it constrained by the underlying program?

[vladimiroltean]

It's not because of the MAC address, it's because in peer delay mode, a port doesn't expect to have more than one peer. The presence of those extra peers on the common Ethernet segment is, as mentioned repeatedly, caused by the hub which is PTP unaware. Replacing that device with a PTP aware switch would solve the problem by speaking peer delay individually with all endpoint devices, as well as with the central LS1021A-TSN.

[jack04060201]

It's not because of the MAC address, it's because in peer delay mode, a port doesn't expect to have more than one peer. The presence of those extra peers on the common Ethernet segment is, as mentioned repeatedly, caused by the hub which is PTP unaware. Replacing that device with a PTP aware switch would solve the problem by speaking peer delay individually with all endpoint devices, as well as with the central LS1021A-TSN.

I don't have that many devices at hand, so I will try using one of the PCs on the hub as a master to synchronize with the other PC using an additional port. It may not be the good solution, but it could serve as an alternative.

Anyway, thank you for your help and suggestions. they have been very helpful to me.

[vladimiroltean]

When I use E2E, I don't receive any packets from the bridge, and all endpoints are in the "selected local clock as best master" state.

If you configure the LS1021A-TSN as an E2E boundary clock, your endpoints should be able to synchronize with it. I don't see why that shouldn't work. I think you left the LS1021A-TSN in P2P and only switched the endpoints to E2E.

[jack04060201]

When I use E2E, I don't receive any packets from the bridge, and all endpoints are in the "selected local clock as best master" state.

If you configure the LS1021A-TSN as an E2E boundary clock, your endpoints should be able to synchronize with it. I don't see why that shouldn't work. I think you left the LS1021A-TSN in P2P and only switched the endpoints to E2E.

I did have concerns about this issue, so I tried both configurations. When using P2P mode with E2E endpoints, I encountered Pdelay_req warnings. However, when using E2E mode, nothing happened, and there were no packets captured in Wireshark.

[vladimiroltean]

On which station did you run wireshark? If you run "tcpdump -i swpN -e -n -Q in" (replace N with the port number) on the LS1021A-TSN, is there nothing there?