Jetson Nano Pinmux Questions

I am attempting to access the Jetson Nano Developer Kit’s 40 pin header pins through DMA and am running into strange issues on many of the pins. I am trying to read from board pins 27, 28, 5, 3, 35, 38, 40, and 12. I have flashed the Nano with a custom pinmux which I have attached. Strangely, only pins 27, 28, 5, and 3 are working properly. All other pins seem to be receiving incorrect voltages from my peripheral devices. The modifications I have made to pinmux are listed (here). Additionally, I have set the Ext. pull-up value for pins 27, 28, 5, and 3 to 0 (blank cell). Does this have something to do with why only these pins are working? I am also confused as to what the purpose of the 3.3V tolerance enable and the external pull-up value columns are in the spreadsheet. Is the external pull-up meant to be a resistor outside the board or is it configured internally? Also, Column AA gives each pin a set pu, pd, or z value, but column AU allows these states to be selected through a dropdown list. Is it an issue of the values for a pin in columns AA and AU differ? As a final note, my attempts to get internal pullup resistors working through pinmux was not successful so I am using external pullup resistors on all input pins. Could this be contributing to the voltage issue on all pins besides 27, 28, 5, and 3?

hello ian.strothers,

please note there’re some pins with “Alternate Function”, you may access Jetson Nano Module Data Sheet, please check [3.3 GPIO Pins] for reference.
there’s level shifter with resistor. please also access Application Note for the 40-Pin expansion header GPIO usage considerations for details.

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