Subsystem UTC acquisition

UTC acquisition

The AMVR is built around a headless Raspberry Pi base as all required software is available for this hardware. Unfortunately, the Raspberry Pi is missing a realtime clock. For an airfield manager purposes precision time is needed for both, the human and its radar engine. This holds true even if there is almost no internet connectivity for use in field. The AMVR design accesses both, network NTP servers as well as a local GPS receiver attached. For initially setting the clock at boot, a startup script is needed, because NTP does not sync to a GPS feed if clock to time offset exceeds 4 hours. After that initial set, NTP syncs seamlessly to the time feeds available.

In the code section a bash script as well as addtional Raspberry Pi configuration is given to fulfill this task at startup. https://github.com/rueckwaertsflieger/AMVR/tree/master/time-sync