ERROR: Get data of the DMA_SxNDTR register

Question

I'm using Discovery kit with STM32F407VG and I want to receive data via the USART2 with DMA mode. I set DMA to the circular mode. In the DMA peripheral, It has a register to handle number of data items to transfer. I access it via uint16_t pointer(pNumberData) with casting method, and then get the value of this register base on the pNumberData pointer, the MCU has a IRQ(HardFault exception). If I use 32-bit type of the pointer instead of 16-bit type of the pointer, the MCU has not problem.

I have debug run-time in the stm32cube IDE, I see that the FORCED bit of HSFR register was been enable to 1.

Refer ARM Documentation but I don't know what reason.

This code is the configuration for DMA:

/**
 * @brief UART MSP Initialization
 * This function configures the hardware resources used in this example
 * @param huart: UART handle pointer
 * @retval None
 */
void HAL_UART_MspInit(UART_HandleTypeDef* huart)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  if(huart->Instance==UART4)
  {
  /* USER CODE BEGIN UART4_MspInit 0 */

  /* USER CODE END UART4_MspInit 0 */
    /* Peripheral clock enable */
    __HAL_RCC_UART4_CLK_ENABLE();

    __HAL_RCC_GPIOA_CLK_ENABLE();
    __HAL_RCC_GPIOC_CLK_ENABLE();
    /**UART4 GPIO Configuration
    PA1     ------> UART4_RX
    PC10     ------> UART4_TX
    */
    GPIO_InitStruct.Pin = GPIO_PIN_1;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF8_UART4;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = GPIO_PIN_10;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF8_UART4;
    HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);

  /* USER CODE BEGIN UART4_MspInit 1 */

  /* USER CODE END UART4_MspInit 1 */
  }
  else if(huart->Instance==USART2)
  {
  /* USER CODE BEGIN USART2_MspInit 0 */

  /* USER CODE END USART2_MspInit 0 */
    /* Peripheral clock enable */
    __HAL_RCC_USART2_CLK_ENABLE();

    __HAL_RCC_GPIOA_CLK_ENABLE();
    /**USART2 GPIO Configuration
    PA2     ------> USART2_TX
    PA3     ------> USART2_RX
    */
    GPIO_InitStruct.Pin = GPIO_PIN_2|GPIO_PIN_3;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF7_USART2;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

    /* USART2 DMA Init */
    /* USART2_RX Init */
    hdma_usart2_rx.Instance = DMA1_Stream5;
    hdma_usart2_rx.Init.Channel = DMA_CHANNEL_4;
    hdma_usart2_rx.Init.Direction = DMA_PERIPH_TO_MEMORY;
    hdma_usart2_rx.Init.PeriphInc = DMA_PINC_DISABLE;
    hdma_usart2_rx.Init.MemInc = DMA_MINC_ENABLE;
    hdma_usart2_rx.Init.PeriphDataAlignment = DMA_PDATAALIGN_BYTE;
    hdma_usart2_rx.Init.MemDataAlignment = DMA_MDATAALIGN_BYTE;
    hdma_usart2_rx.Init.Mode = DMA_CIRCULAR;
    hdma_usart2_rx.Init.Priority = DMA_PRIORITY_LOW;
    hdma_usart2_rx.Init.FIFOMode = DMA_FIFOMODE_DISABLE;
    if (HAL_DMA_Init(&hdma_usart2_rx) != HAL_OK)
    {
      Error_Handler();
    }

    __HAL_LINKDMA(huart,hdmarx,hdma_usart2_rx);

    /* USART2_TX Init */
    hdma_usart2_tx.Instance = DMA1_Stream6;
    hdma_usart2_tx.Init.Channel = DMA_CHANNEL_4;
    hdma_usart2_tx.Init.Direction = DMA_MEMORY_TO_PERIPH;
    hdma_usart2_tx.Init.PeriphInc = DMA_PINC_DISABLE;
    hdma_usart2_tx.Init.MemInc = DMA_MINC_ENABLE;
    hdma_usart2_tx.Init.PeriphDataAlignment = DMA_PDATAALIGN_BYTE;
    hdma_usart2_tx.Init.MemDataAlignment = DMA_MDATAALIGN_BYTE;
    hdma_usart2_tx.Init.Mode = DMA_NORMAL;
    hdma_usart2_tx.Init.Priority = DMA_PRIORITY_LOW;
    hdma_usart2_tx.Init.FIFOMode = DMA_FIFOMODE_DISABLE;
    if (HAL_DMA_Init(&hdma_usart2_tx) != HAL_OK)
    {
      Error_Handler();
    }

    __HAL_LINKDMA(huart,hdmatx,hdma_usart2_tx);

  /* USER CODE BEGIN USART2_MspInit 1 */

  /* USER CODE END USART2_MspInit 1 */
  }

}

The main code:

uint16_t *pNumberData = NULL;
uint8_t buff[BUFF_SIZE] = { 0U };

.... 

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{
  /* USER CODE BEGIN 1 */
    uint16_t tmp = 0x00U;
  /* USER CODE END 1 */

  /* MCU Configuration--------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* USER CODE BEGIN Init */

  /* USER CODE END Init */

  /* Configure the system clock */
  SystemClock_Config();

  /* USER CODE BEGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_USART2_UART_Init();
  MX_UART4_Init();
  /* USER CODE BEGIN 2 */
  HAL_UART_Receive_DMA(&huart2, buff, BUFF_SIZE);
  pNumberData = (uint16_t *)&hdma_usart2_rx.Instance->NDTR;
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
      tmp = *pNumberData;
      printf("*pNumberData %d\r\n", *pNumberData);
      printf("tmp %d\r\n", tmp);
      HAL_Delay(500);
  }
  /* USER CODE END 3 */
}

What is the reason of the behavior in 16-bit case? Thanks for taking your time to read this!

Answer 1

According to the reference manual [RM0090 Rev 19, page 325]:

The DMA registers have to be accessed by words (32 bits).

I don't know the reason behind this constraint, but why not just honor it?