precise RTC with wake up functionality

The RTC is part of the ZSOM-Mini and can be implemented in any custom design since it uses just 2 FPGA IOs for its I2C interface.

The precise RTC does not set the system clock directly. The sbRIO9651 has its own internal RTC.

The RTC is backed up by the optionally available backup battery.

Th ZSOM mini can be woken up at the previously set alarm time.

The Target WONT be woken up under the following conditions:

1. No power is applied at the set alarm time. The target has to be woken up manually after the power is reapplied.
2. The target is already (or still) running. The Alarm state can be monitored trough the I2C interface. Make sure the time between shut down and the set alarm time is more than 30s
3. The backup battery does not provide backup voltage to the RTC

The ZSOM-Mini can be powered down by cutting the power, setting the kill_signal via FPGA or by tying the Go input (pin 1) to GND (eg. pin 2) for more than 5s.