We're developing a compute module board, and added the undervoltage circuit.
Unfortunately, I cannot find where to PWR_LOW_N is actually connected. I have found some saying it's connected to GPIO 35 and GPIO 135 (which seemed to be a typo to me).
Where should we connect the undervoltage detection so the kernel can work directly with it? Or is it something that isn't needed?
Thanks and with best regards, Tom
What did you decide to do, Tomas?
I believe that the schematic of the Under Voltage Detect function was provided by RPi (here: https://www.raspberrypi.org/documentation/hardware/computemodule/schematics.md) simply to show how the detection was done on RPi modules. I suppose the idea of putting the circuit with the CM schematics was that you could do something similar with a CM... so your question about where you should connect it is reasonable given that PWR_LOW_N isn't available on the SODIMM. The function doesn't appear to be on the CMIO development board (though with reduced schematics nothing's certain) and isn't mentioned in the datasheet (https://www.raspberrypi.org/documentation/hardware/computemodule/RPI-CM-DATASHEET-V1_0.pdf) either. Presumably you could use the circuit (or a multi-rail monitor device eg LTC132 if your application is multi-rail), and connect to a GPIO pin.
