Hardware used in this project is an old PulseSecure PSA3000 unit, which is a Supermicro server in disguise.

Specification:

• Celeron J1900
• 4 GB of DDR3 RAM
• X10SBA-L motherboard
• Intel i210 NIC
• LEA-M9T GPS receiver
• Generic GPS antenna

GPS receiver is installed inside server chassis and powered using 3,3 V available in the server.

UART connection is connected to goldpin serial COM port /dev/ttyS1 on the motherboard using generic UART-RS232 converter.

PPS signal is configured in the module using U-center software to be 8 Hz 50% pulse width square wave, which is connected to the SDP0 pin in SDP header on the NIC.

GPSD is responsible for communication on serial port and putting the timestamp read from the GPS module into SHM in the system. It gives the system current timestamp set after each message is received and processed.

Chrony is responsible for receiving an event triggered on the SDP0 pin by either rising or falling edge of the PPS signal. Due to hardware and driver constraints there was no easy way to configure event triggering, that is why LEA-M8T produces 8 Hz signal, but events are triggered in 16 Hz pace - both on rising and falling edges of the signal.

./testptp -d /dev/ptp0 -e 17
external time stamp request okay
event index 0 at 1791542531.013602988
event index 0 at 1791542531.076101100
event index 0 at 1791542531.138599212
event index 0 at 1791542531.201097324
event index 0 at 1791542531.263595460
event index 0 at 1791542531.326093572
event index 0 at 1791542531.388591684
event index 0 at 1791542531.451089804
event index 0 at 1791542531.513587916
event index 0 at 1791542531.576086044
event index 0 at 1791542531.638584164
event index 0 at 1791542531.701082276
event index 0 at 1791542531.763580388
event index 0 at 1791542531.826078524
event index 0 at 1791542531.888576636
event index 0 at 1791542531.951074748
event index 0 at 1791542532.013572868