I was able to reproduce your results. I tried A0 thru A10 (skipping A2/A3 since those are are REPL UART) and on all of them except A9, the pullup seemed to work fine.
Since A9 is used for VBUS sensing, I theorized that some USB circuitry was being connected.
I modified your mpconfigbord.h file and commented out the
line, but that didn't seem to make any difference.
Code: Select all
#define MICROPY_HW_USB_VBUS_DETECT_PIN (pin_A9)
You may need to completely disable the USB device completely (which IIRC is non-trivial with the current codebase) in order to get the internal A9 pullup to behave properly.