The AXP209 used on the pcDuino3 has a pin (30) for connecting a backup battery for the RTC. I have successfully soldered on a 3V rechargeable battery to that pin and it is correctly allowing the internal RTC of the A20 to keep ticking – left it overnight unplugged and the time was correct this morning (no network connection).
There is however a problem. The default value for the backup battery register (0x35) is set to disable charging of the battery. I need to enable it by writing the value 0xA3 to this register.
Does anyone know how to write to a registers on the PMU?
sudo apt-get install i2c-tools sudo i2cset -f -y 0 0x34 0x35 0xA3
Just a follow up. This is still working fine.
I’ve attached a picture of how I attached the battery to the board. It’s a tad fiddly, but do-able.