I came across some techniques for measuring the internal Vcc without the need for a precious pin:
I was wondering if anyone had tried using this measurement to trigger an EEPROM write during shutdown (to save active parameters). Probably a dozen bytes or so.
I'm running at 5V, and could probably set brownout to 2.7V to allow some time (or even 1.8V?) I can add a cap, within reason, to prop up the VCC as needed, and obviously switch off LED's and other things that could consume power.
I'm just not sure if this technique is accurate/reliable enough to ensure safe eeprom storage; I would have expected this to be a common method if it was.
Currently designing for ATMega88.