I’m working on a design incorporating a Gumstix Overo AirSTORM-Y COM, and I note that it can accommodate a backup battery. I understand that this is handled by the on-board TPS65950 PMIC, which includes a real-time clock module.
However, the Overo documents don’t mention an RTC, so I’m writing to find out if the RTC in the PMIC is functional on the AirSTORM-Y. Is it?
Yes, the RTC in the AirSTORM-Y PMIC is functional. You can connect a backup battery to pin 52 on connector J1.
On the Gumstix Tobi board (https://store.gumstix.com/tobi.html), I've tested the RTC using one of these: https://www.digikey.com/products/en?keywords=ML-621S%2FZTN
To read the RTC clock, you can use the linux userspace command: "sudo hwclock -r"
https://www.gumstix.com/images/overo_signals_latest.pdf
Looking at page 7, the Signal "VBACKUP" is what you're interested in - although, I agree, it's not made that clear it can be used for the RTC backup battery. Rest assured, it can be.
And just to be clear, J1 Pin 52 is directly connected to ball "M14", Signal "BKBAT" on the TPS65950.
