Reply To: time synchronization without gps
You could do that, but it might take some work. The UM7 has a free-running hardware timer with better than microsecond resolution that starts running when it powers on. It uses incoming PPS pulses and GPS packets to perform a second-order calibration on that timer, synchronizing it to GPS time. The PPS pulse is expected to come in at 1 second intervals with very high accuracy, on the second. Once the GP9 receives the PPS pulse, it uses the next GPS RMC packet to extract the time at which the pulse went high.
To synthesize the timing synchronization without GPS, you’d need to have a piece of hardware that outputs a PPS pulse once a second, and that sends a NMEA RMC packet immediately after each pulse so that the UM7 can extract the time.