The stm32l432 lacks the PORRSTF flag that other stm32 processors have, so I don't see a way to reliably detect a power-off/on event. I tried parking a bit in the backup registers, but it doesn't appear that this is cleared without waiting for stray capacitors to discharge, which would be fine if I understood the threshold. The reference manual includes this cryptic note about when the backup domain is reset:
"VDD or VBAT power on, if both supplies have previously been powered off"
But what levels ? I need to know when a significant power glitch has occurred, but how ?
Is there a reliable test ?