Hello,
I have a Witty Pi 4 on order from Ada Fruit.
Can I assume with the Witty Pi 4 the RPi UART Rx data pin is available for Data In to the RPi?
If I bring GPS data into the UART Rx pin, how would I disable / override NTP time being used to set the hardware RTC? I assume that if I avoid setting the 'seconds' time between 55 and 00, I can leave the years, months, weekdays, days, hours, and minutes untouched until a full time check / set is done once a day.
Yes, you can use the Raspberry Pi's UART RXD pin (GPIO15) while Witty Pi 4 is connected.
Witty Pi 4 does not occupy the UART. It only monitors the voltage on TXD (GPIO14) to detect when the Raspberry Pi has shut down. The monitoring circuit filters out brief voltage changes during normal serial communication, so UART communication can still work normally. We have tested this scenario.
You can find more details in these previous discussions:
https://www.uugear.com/forums/technial-support-discussion/witty-pi-4-l3v7-and-serial-port/
https://www.uugear.com/forums/technial-support-discussion/witty-pi-gpio-conflicts/
Regarding using GPS instead of NTP and implementing your own RTC synchronization strategy, these are system integration and application design matters beyond the scope of Witty Pi product support. You would need to develop and test your own solution.