Unexpected PB3 behavior with connected st-link

[shiawasenapluto]

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Hello! During project debugging i encountered with follow situation. I have a led connected to PB3 pin (configured as output push-pull with low level by default) on STM32F103 and it turns on during debugger connecting and programming (i program empty flash) process and before the main program entering. I full erased flash then with STM32CubeProgrammer, but PB3 still raises high while debugger(ST-Link V2) is connected.
After power toggling i downloaded under IAR debug with st-link other firmware and the pin behaves as expected (stays low).

I also generated empty project with CubeMx (only external oscillator and SWD enabled) to see how PB3 would behave. After IAR debug session started it stays low. So, i suppose the problem is in firmware, but i can't understand where i should search it.  All projects are generated in CubeMx 6.13 and debugged with IAR 9.60, HAL drivers version is V1.8.5

[Andrew Neil]

Welcome to the forum.

Please see How to write your question to maximize your chances to find a solution for best results; in particular:

• What board are you using - if a custom board, show schematics;
• Are you sure this is a genuine STM32, and a genuine ST-Link?

[shiawasenapluto]

Hello! Thanks for answering. I don't think i could share schematics of my board (the developer is not me). I'm sure about controller genuineness and can't say the same about debugger.

[TDK]

PB3 is SWO by default. Makes sense that it may not be idle.

Once you set it to output, it should behave as an output. With flash erased, it will remain as SWO.

[shiawasenapluto]

Hello! Thanks for answering. The point is that PB3 remains high even when configured as output and brought low. I checked generated GPIO initialization function and it seems to be correct. Also, still strange for me, that if PB3 is JTDO by default, i don't observe same behavior with another firmware while using the same drivers version on the same board and with the same debugger.

[TDK]

Show contents of the GPIOB registers when the pin is configured as output low and stays high.