Specific ConnectX-6 Dx boards are equipped with an onboard GNSS receiver.
This is the GNSS receiver detail: UBLOX UBX-m8030
The RF input from the GNSS antenna is supplied to the GNSS receiver through an SMA connector on the bracket. The GNSS receiver contains a PPS output that is routed to the ConnectX-6Dx PPS input. Additionally, it generates Time of Day messages in NMEA format which are sent towards the host server over a serial connection, emulated over USB.
In recent Linux kernels, the required kernel module (cdc-acm) is already included.