STM32CubeMX generates incorrect code for GPIO initialisation with LL-libraries (STM32F1xx)

I beleive that I have discovered a bug where CubeMX v4.27.0 generates incorrect code for GPIO initialisation.

Here is the story:

Pins have been preconfigured via Pin Configuration menu in the CubeMX app the following way:

• PC14 as Input with Pull-Up
• PC15 as Output (push-pull) with Low Initial State

Here is the code generated for MX_GPIO_Init() function with my comments added:

 /**/
 LL_GPIO_ResetOutputPin(GPIOC, DO_5V_ENABLE_Pin); // DO_5V_ENABLE_Pin is set to be LOW here
 
 /* ... skipped ... */
 
 /**/
 GPIO_InitStruct.Pin = DI_5V_FUSE_STAT_Pin;
 GPIO_InitStruct.Mode = LL_GPIO_MODE_INPUT;
 GPIO_InitStruct.Pull = LL_GPIO_PULL_UP;
 LL_GPIO_Init(DI_5V_FUSE_STAT_GPIO_Port, &GPIO_InitStruct);
 
 /**/
 GPIO_InitStruct.Pin = DO_5V_ENABLE_Pin;
 GPIO_InitStruct.Mode = LL_GPIO_MODE_OUTPUT;
 GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_LOW;
 GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
 LL_GPIO_Init(DO_5V_ENABLE_GPIO_Port, &GPIO_InitStruct); // DO_5V_ENABLE_Pin goes HIGH after initialisation

As you see, the DO_5V_ENABLE_Pin ends up HIGH after initialisation although STM-code tried setting it LOW in the beginning.

Why?

Because the GPIO_InitStruct structure is re-used for each pin being configured but not all fields are initialised all the time.

It is obvious that line 9​ sets the 'Pull' field to HIGH and later, when another pin is configured as Output, the 'Pull' field is never updated but still gets written to the corresponding ODR-register by the LL_GPIO_SetPinPull() function called by the LL_GPIO_Init() function (file 'stm32f1xx_ll_gpio.c'):

 /* Pull-up Pull-down resistor configuration*/
 LL_GPIO_SetPinPull(GPIOx, currentpin, GPIO_InitStruct->Pull);

That's how the pin set to have its initial value to be LOW ends up being HIGH as a result.

The solution is either to initialise all fields of the structure explicitly OR update the LL_GPIO_Initi() function so it only calls LL_GPIO_SetPinPull() function when we the pin Mode is set to Input, i.e. change this code in the 'stm32f1xx_ll_gpio.c' file:

 /* Pull-up Pull-down resistor configuration*/
 LL_GPIO_SetPinPull(GPIOx, currentpin, GPIO_InitStruct->Pull);

to this code:

 /* Pull-up Pull-down resistor configuration - ONLY FOR INPUTS (STM bug fix) */
 if (GPIO_InitStruct->Mode == LL_GPIO_MODE_INPUT)
 {
 	 LL_GPIO_SetPinPull(GPIOx, currentpin, GPIO_InitStruct->Pull);
 }

Hope it saves time someone ;)

Cheers.

#[STM32 MCUs]​ #STM32CubeMX​ #Ll-gpio​