For Ultra96 clock realtime and frequency synchronization with a GPS/GNSS disciplined oscilator here is one solution:
This KiCAD designed open-hardware Ultra96 compatible extension board is now available as a product:
* lightside-instruments.com/.../
Vivado project and source code is available as part of the "Network Programabillity kit for Ultra96" project:
* www.hackster.io/.../network-programmability-kit-for-ultra96-07435c