STM32CubeIDE – Why Does the Debugger Always Stop on HAL_Init()?

I found the problem of one of the questions, so I added it for other people's reference, since it is a non-trivial default:

When using the STM32CubeMX which I do, whenever a project is made, by default the following item is selected:

• SYS, Debug: No Debug

This causes that the following code is generated in HAL_MspInit:

__HAL_AFIO_REMAP_REMAP_SWJ_DISABLE();

As soon as the debugger passes this command (which is one of the first commands in HAL_Init which is called in main(), the debugger loses connection and even a new debug session cannot be started.

It can be easily fixed with setting to

• SYS, Debug: Serial Wire

(which is also called SWD: Serial Wire Debug, and is supported by ST Link 2).

This causes that the following code is generated in HAL_MspInit:

__HAL_AFIO_REMAP_SWJ_NOJTAG();

And debugging works as usual.

I have witnessed this on other STM32 devices I have used. The basic issue is that in some cases there is a read-modify-write operation to I2C control register which ends up setting STOP and START bits simultaneously. ST HAL has had similar bugs for years, it is not 100% reliable, and must be fixed by accessing the I2C peripheral registers correctly in every situation (according to Reference Manual and Errata). This error gets triggered more often if there is other stuff happening as well (interrupts at critical moment or other tasks running under RTOS). They never seem to get it right, and each time they make changes to fix something, it works a bit differently, but it is never completetly fixed. For this reason it's best to make your own I2C handling code that fits your needs, even if it means to use the existing HAL as a base for your modifications.