we have a custom carrier board with the gpio388 (GPIO8_ALS_PROX_INT) exposed on an expansion header. Because we want to use 3.3V, we use a similar level shifter as implemented on the devkit (mosfet Q27). Using the gpio as output, everything is working as expected. When configured as input, the voltage on the source pin of the mosfet drops to 0.8V which activates the mosfet. Therefore, the jetson does not recognize any voltage change on the 3.3V side, it always shows value 0.
I also measured the voltage levels on the devkit. Here, I can also see some voltage drop, when configured as input, but the level on the low voltage side is slightly higher than on our custom board (1V > 0.8V, maybe because we use a different mosfet (bss138)) which makes the jetson recognize it as high. Nevertheless, I would assume that the voltage level should be nearly 1.8V at the gpio.
So it seems to be, that the gpio has a small pull down resistor. Can you confirm this? Would you suggest to change the value of the pull up resistor on our carrier board (currently 47k, like on the devkit) or is it possible to change the value of the internal pull down via software?