Master Clock Setup Using RPi CM4 - Suggestions Required

[aravind-subbiah]

We are using Raspberry Pi CM4 with CM4 IO Board as our Master device, with u-blox (ZED-F9T) GNSS receiver to provide 1pps input and Time of Day messages via USB connection. We want a master setup where we can get 1pps out from master PHC and compare if it’s synced with respect to the source on a TIC.

• The setup was done using https://github.com/jclark/rpi-cm4-ptp-guide/tree/main
• We used ts2phc to sync the PHC (selected source nmea and 1 pps input from J2.9 – SYNC_OUT pin)
• From the repo, the boot config using ‘pps-gpio’ to enable GPIO pin 18 was done, but we could not get any output on the TIC
• Then we experimented to produce 1 pps out from GPIO pin 18 using PIGPIO daemon. The results were not good since it could not produce proper output.
• Also, we understood that the PIGPIO is producing output using SYSTEM SOFTWARE clock rather than the PHC. So, we tried to sync software clock using phc2sys.
• Still the results were bad.

After this we tried to use Intel I225-T1 NIC to use its 1588 functionalities.

• We tried to sync from J2.9 pin in RPi CM4 and produce 1 pps out from NIC’s SDP0 pin . The 1 pps was provided out but they were not synced.
• Also, we tried to reverse the pps in and out to see if that will change anything, but no effect. Then we understood that both the CM4 and NIC has separate PHC, that is why when we sync one using ts2phc, the other was just not synced.
• We tried to sync one PHC with ts2phc and another using phc2sys. We did get results but the minimum difference we can get between the source and 1pps out is around 180 us (we want to achieve ns level synchronization). We believe it is because phc2sys is a kernel level synchronization and that’s why the offset.
• Also, we could see for Intel I225-T1 NIC in the path ‘/sys/class/ptp/ptp1/pins/’ that there are multiple SDP pins present to be used, but only the SPD0 was getting used when I use ts2phc for 1pps input or testptp for 1pps output.

It would be really helpful if there can be any suggestions on further workaround on the current situation.