Had I designed it, it would have had a graceful shutdown
procedure…
Technically this is already in place. You just need a $2USD battery.
But anyway, I’ve given this a lot of though, as my buddy forcing me to talk about this in great detail several times. Until he understood what I could do with an external MCU in software.
For a long time, he though he would be able to get away with using an external watch dog. And then he though that we could do all this solely using the PMIC + BBB interrupts. Which is partially true. But the “cant reset because I’m stuck in an odd power state” issue never occurred to him. Something that I’ve personally experienced first hand, several times. Now, after we’ve talked A LOT, and about the various potential situations, we think we’ve got it 100% bullet proof covered.
My own personal preference would be to have an external battery powering the 5V power in, and an external power supply charging that. With again, and MCU ( MSP430G2553 ) communicating back to the BBB. When it’s time to shut down. Really similar to UPS. but my buddy does not like that, he says the cost is too hight. And he is right, it would be.