When I set the AF to 5 on GPIO PB4 of my STM32F769 it hangs. Why?

Oliver Sedlacek · ‎2017-03-17

Posted on March 17, 2017 at 14:34

As per the title, setting the AF of GPIO PB4 to 5 on my STM32F769 hangs the micro. The code was generated by the STM32Cube tool, and all the other GPIO pins get configured fine. I tried changing the code to set the AF to 8 and that hangs, but 'changing' it to 0 (the default) works fine? I've checked the datasheet and AF=5 is what I want because I want to use PB4 for SPI1_MISO.

Any clues?

S.Ma · ‎2017-03-17

Posted on March 17, 2017 at 18:20

Is it a custom board or a Nucleo/Discovery? The alternate 0 is the JTAG reset input signal.

Wonder if the JTAG pin should be disabled first prior to using different alternate, or if there is a specific sequence for this? It might be the same as when developpers want to reuse SWD debug pins for the application (and no longer be able to debug)

Oliver Sedlacek · ‎2017-03-18

Posted on March 18, 2017 at 12:13

It's a custom board. I think you've put your finger on it regarding the JTAG TRST. The debug pods don't seem to need TRST, so I didn't try and hook it up to anything and promptly forgot about it. The STMCube32 tool also didn't throw up any warnings...