BW16 module PA15 not working as a GPIO - suspect External 32k oscillator is grabbing it

FreeRTOS Peripherals
4

I have now tested PA15 using Arduino rather than the SDK.

PA15 is called Pin 9 in the Arduino world

I find that if I write a simple sketch which sets pinMode(9,OUTPUT); and toggling it slowly, I can see the pin changing from 0 to 3.3V and back.

So it is usable as an output.

However, if I now change it to 'pinMode(9,INPUT_PULLUP), I find that once again, the standing voltage on the pin is 1.6V.