GPSDO — management
For frequency and time synchronization of two or more devices, GPSDO (GPS Disciplined Oscillator) is used - a device that functions simultaneously as an external reference signal source and a pulse generator 1PPS (Pulse Per Second). This device provides temporary synchronization and stabilization of the frequency parameters of the system by linking to the reference signals of satellite navigation systems.
To integrate GPSDO into the RITM SDR USRP platform, it is necessary to switch the corresponding interfaces. The output signal of the 1PPS GPSDO device is fed to the 1PPS RITM SDR USRP input connector of the same name to ensure temporary synchronization. The output of the reference oscillator (standard frequency 10 MHz) is connected to the external clock input REF IN to stabilize the frequency parameters of the system.
1 PPS
To control the 1PPS signal, a specialized IP core, PPSTex, is implemented in the RITM SDR USRP architecture. This module provides synchronous capture of an external signal when it is present at the input, and in case of loss of the reference pulse, it switches to autonomous generation mode. At the same time, the kernel restores the time grid based on statistical data on the periods of the 1PPS external signal obtained during previous iterations. In addition, the module supports the generation and broadcasting of its own 1PPS signal to the interface output.
The IP core parameters are controlled through the functions set_ip_core() and get_ip_core(). For more information, see SDR registers.
External/Internal exhaust gas
To install an external exhaust gas, you need to connect the output of the external reference generator to the REF IN input to the RITM SDR USRP.
Cascade system
It is allowed to implement a cascade synchronization scheme for RITM SDR USRP devices, in which the output of the reference signal REF OUT of the master device is connected to the external clocking input REF IN of the slave device. This topology allows you to broadcast a single frequency standard along the instrument chain. An example is shown in the figure.
