PTP Synchronization for OAK 4S-W

zhouquan1103

Now we are testing the PTP synchronization for OAK 4S-W. We have a PTP master which connected with GPS and broadcasts PTP sync data with UDP protocol in the local network.
We already enabled the PTP sync function by setting the parameters as below:

PTP_ENABLE=true

PTP_MODE=slave

PTP_SYNC_FRAMES=true

PTP_SYNC_SYSTEM_CLOCK=true

But in the next step we met questions:
1. We need to config the detail parameters such as E2E or P2P/ UDP or L2 etc.. But we don't know what kind of mode OAK4S-W supports and how to config it.
2. Which function we need to call in our program to get the synchronized timestamp and how about the timestamp format so we can transfer it to UTC time format to check if synchronization is success or not.

Thank you for your help!

SasoTamse

Hi zhouquan1103 - Please refer to our PTP synchronization documentation:

https://docs.luxonis.com/hardware/platform/deploy/data-sync/ptp-sync/

It explains the supported PTP configuration, how to enable it on OAK4 devices, and how to verify that the device clock is synchronized.

You can also use this multi-device synchronization example:

https://github.com/luxonis/depthai-core/blob/main/examples/python/Misc/MultiDevice/multi_device_frame_sync.py

The example demonstrates how to enable PTP frame synchronization with TIME_PTP, read frame timestamps, compare timestamps between devices, and determine whether the frames are synchronized.

Thank you,
Sašo

zhouquan1103

SasoTamse Thank you very much. Could you please tell us which kind of mode OAK-4S supports in the below four choices.
1. E2E L2;
2. E2E UDP；
3. P2P L2；
4. P2P UDP;
Because in our local network there are some other devices such as laser lidar. The lidar can't support all the four. We need to choose the correct one that OAK 4S and lidar can both support.

Thank you.

zhouquan1103

Additional: if there is a varaible, which we can get in our c++ program to verifty if the camera already synchronized or locked with the PTP master according to its realtime value.

SasoTamse

zhouquan1103

OAK4 currently uses E2E over UDP/IPv4.

Please ensure that the lidar and PTP grandmaster are configured for the same PTP domain and E2E UDP transport.

There is currently no direct DepthAI C++ variable that reports the PTP lock state.

With PTP_SYNC_SYSTEM_CLOCK=true, you can read the PTP-synchronized system timestamp from each frame:

auto timestamp = frame->getTimestampSystem();

if(timestamp.has_value()) {
    auto nanoseconds =
        std::chrono::duration_cast<std::chrono::nanoseconds>(
            timestamp->time_since_epoch()
        ).count();

    std::cout << "Timestamp: " << nanoseconds << " ns" << std::endl;
}

getTimestampSystem() returns the device system-clock timestamp, which can be synchronized by PTP. You can compare it with the timestamp from your lidar or GPS/PTP system to verify synchronization.

For frame synchronization, the C++ example checks the timestamp difference between devices and considers them synchronized when the difference is below the configured threshold:

https://github.com/luxonis/depthai-core/blob/main/examples/cpp/Misc/MultiDevice/multi_device_frame_sync.cpp

The relevant logic reads the frame timestamps, calculates the maximum timestamp difference, and reports whether the frames are in sync.

Please use DepthAI 3.8.0 or newer and Luxonis OS 1.35.0 or newer for the latest OAK4 PTP support.

Thank you,
Sašo

mod199818

SasoTamse Thanks for the support! We can now read PTP synced timestamps with getTimestampSystem() as you suggested.

But there’s a problem: the timestamp output from this function is consistently 37 seconds offset against our lidar (separate device, same PTP domain & E2E UDP setup). Both devices sync to the same PTP grandmaster.

Have you run into this fixed 37s time offset problem? Any advice to resolve it?

Thanks

SasoTamse

Hi mod199818 - A fixed 37-second offset usually means TAI vs UTC, not a PTP sync failure.

PTP commonly uses TAI, which is currently 37 seconds ahead of UTC. Please check that your grandmaster announces:

currentUtcOffset = 37
currentUtcOffsetValid = 1
ptpTimescale = 1

Also check whether the lidar timestamp is UTC or TAI.

If the OAK timestamp is still exactly 37 seconds off with these settings correct, please send us the Luxonis OS version and grandmaster configuration so we can investigate further.

Thank you,
Sašo