Hardfault (FORCED, IMPRECISERR) when erasing flash page. [STM32WB55]

[TomC]

Hi there,

I am receiving a hardfault when erasing pages of flash, seemingly randomly. I can recreate the issue somewhat consistently if I rapidly erase flash pages. I have followed the example project from the STM32WB firmware package (erase flash example). 

This is my function for erasing flash.

flash_status_t user_flash_erase_page(uint8_t page_number, uint8_t number_of_pages)
{
//  static FLASH_EraseInitTypeDef EraseInitStruct = {0};
  static FLASH_EraseInitTypeDef EraseInitStruct = {0};

  if(HAL_FLASH_Unlock()!= HAL_OK)
  {
    return FLASH_ERROR;
  }

  /* Clear OPTVERR bit set on virgin samples */
  __HAL_FLASH_CLEAR_FLAG(FLASH_FLAG_OPTVERR);

  EraseInitStruct.TypeErase = FLASH_TYPEERASE_PAGES;
  EraseInitStruct.Page = page_number;
  EraseInitStruct.NbPages = number_of_pages;

  uint32_t page_error = 0;

  if (HAL_FLASHEx_Erase(&EraseInitStruct, &page_error) != HAL_OK)
  {
    HAL_FLASH_Lock();
    return FLASH_ERROR;
  }
  else
  {
    HAL_FLASH_Lock();
    return FLASH_OK;
  }

  return FLASH_OK;
}

Specifically I will hardfault when trying to perform HAL_FLASH_Lock( ) when HAL_FLASHEx_Erase fails (line 23 in the code snippet above)

if (HAL_FLASHEx_Erase(&EraseInitStruct, &page_error) != HAL_OK)
{
  HAL_FLASH_Lock();
  return FLASH_ERROR;
}

 
From the reference manual (RM0434 - Section 3.10.5 FLASH_CR) for the STM32WB I see that 

"This register (FLASH_CR) must not be modified when CFGBSY in Flash memory status register
(FLASH_SR) is set. This would result in... a bus error, if CFGBSY is set due to a double-word programming sequence and the write to FLASH_CR is performed after the first word is sent for programming and before
the second."

The hardfault I receive is a bus error

Further, when I inspect the CFGBSY bit in the FLASH_SR register I find that it is set

So I figure the fault occurs because the program tries to modify the FLASH_CR register when the CFGBSY bit is set in the HAL_FLASH_Lock( ) function

/**
  * @brief  Lock the FLASH control register access.
  * @retval HAL Status
  */
HAL_StatusTypeDef HAL_FLASH_Lock(void)
{
  HAL_StatusTypeDef status = HAL_OK;

  /* Set the LOCK Bit to lock the FLASH Registers access */
  /* @Note  The lock and unlock procedure is done only using CR registers even from CPU2 */
  SET_BIT(FLASH->CR, FLASH_CR_LOCK);

  /* verify Flash is locked */
  if (READ_BIT(FLASH->CR, FLASH_CR_LOCK) == 0U)
  {
    status = HAL_ERROR;
  }

  return status;
}

The specific pages of flash that I am modifying (erasing) are 167 - 170. According to the memory map for the STM32WB55 this is okay

[TDK · Accepted solution]

Why is HAL_FLASHEx_Erase failing? By that I mean what is in pFlash.ErrorCode and what address is in page_error when the call returns HAL_ERROR?

[Joe WILLIAMS]

Hi TomC

Your case is being reviewed through the online support portal.

Thank you for your patience.

Kind Regards

Joe WILLIAMS

STMicro Support

[TomC]

Hi TDK,

Thank you for your response, I believe the problem was caused by me overwritting some memory with memcpy() somewhere else hence the IMPRECISERR. I will keep in mind to check the error code next time this happens.

[TomC]

Hi Joe,

I believe I caused this problem by overwritting memory with a memcpy () elsewhere in my program. Thank you for your response.