USB CDC and FreeRTOS

[MK..1]

Hi

in different posts in forum I read ST's USB library is not thread safe. There are no examples with USB CDC and FreeRTOS.

Is that true?

Thx

[Pavel A.]

Yes. If you don't know why your software works, you have a potential risk.

[FBL]

Hi @MK..1 

Usage of malloc(), free(), or any other function implicitly calling these functions is not safe in multi-threaded systems even in bare metal or RTOS systems. AN5731 provides some guidelines for ensuring thread safety.

[MK..1]

Hi @FBL 

how does AN5731 relate to ST USB library as it is not using malloc()?

I didn't find any malloc or free in the ST USB library!

Is there a specific reason why there is no CDC and FreeRTOS example project?

Thanks

[FBL · Accepted solution]

Hi @MK..1 

ST USB middleware is not explicitly using malloc() and free(), but it is crucial to configure it to use static memory allocation to ensure thread safety.

/**
  * @brief  Static single allocation.
  * @param  size: Size of allocated memory
  * @retval None
  */
void *USBD_static_malloc(uint32_t size)
{
  static uint32_t mem[(sizeof(USBD_CDC_HandleTypeDef)/4)+1];/* On 32-bit boundary */
  return mem;
}

/**
  * @brief  Dummy memory free
  * @param  p: Pointer to allocated  memory address
  * @retval None
  */
void USBD_static_free(void *p)
{

}