功能實現背景介紹

本項目中，需要使用STM32的USART6串口與FPGA板（下位機）通信，需要發送和接收數據，有報文應答機制。

使用的報文規則如表格所示

板間報文的通信協議，校驗使用的是和校驗

U8 TX_CheckSum(U8 *buf, U8 len) //buf為數組，len為數組長度
{ 
    U8 i, ret = 0;
    for(i=0; i< len; i++)
    {
        ret += *(buf++);
    }
     ret = ~ret;
    return ret;
}
U8 RX_CheckSum(U8 *buf, U8 len) //buf為數組，len為數組長度
{ 
    U8 i, ret = 0;
     for(i=0; i< len; i++)
    {
        ret += *(buf++);
    }
    ret = ret;
    return ret+1;
}

發送和接收的報文要滿足不定長

HAL庫的中斷接收函數

如果要直接使用HAL庫的中斷接收函數，也就是HAL_UART_Receive_IT()函數

HAL_UART_Receive_IT(&huart6,UART6_RxBuffer,5);              //下位機FPGA

在使用時，選擇串口，選擇接收的緩沖區，選擇接收長度。

/**
  * @brief  Receives an amount of data in non blocking mode.
  * @note   When UART parity is not enabled (PCE = 0), and Word Length is configured to 9 bits (M1-M0 = 01),
  *         the received data is handled as a set of u16. In this case, Size must indicate the number
  *         of u16 available through pData.
  * @param  huart Pointer to a UART_HandleTypeDef structure that contains
  *               the configuration information for the specified UART module.
  * @param  pData Pointer to data buffer (u8 or u16 data elements).
  * @param  Size  Amount of data elements (u8 or u16) to be received.
  * @retval HAL status
  */
HAL_StatusTypeDef HAL_UART_Receive_IT(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size)
{
  /* Check that a Rx process is not already ongoing */
  if (huart- >RxState == HAL_UART_STATE_READY)
  {
    if ((pData == NULL) || (Size == 0U))
    {
      return HAL_ERROR;
    }

    /* Process Locked */
    __HAL_LOCK(huart);

    huart- >pRxBuffPtr = pData;
    huart- >RxXferSize = Size;
    huart- >RxXferCount = Size;

    huart- >ErrorCode = HAL_UART_ERROR_NONE;
    huart- >RxState = HAL_UART_STATE_BUSY_RX;

    /* Process Unlocked */
    __HAL_UNLOCK(huart);

    /* Enable the UART Parity Error Interrupt */
    __HAL_UART_ENABLE_IT(huart, UART_IT_PE);

    /* Enable the UART Error Interrupt: (Frame error, noise error, overrun error) */
    __HAL_UART_ENABLE_IT(huart, UART_IT_ERR);

    /* Enable the UART Data Register not empty Interrupt */
    __HAL_UART_ENABLE_IT(huart, UART_IT_RXNE);

    return HAL_OK;
  }
  else
  {
    return HAL_BUSY;
  }
}

這個函數本質上其實不是中斷接收函數，只是配置函數，配置開啟中斷的信息，并且接收多少定長的數據結束本數據接收，串口的中斷接收還是在中斷中進行。

我們本次的長度雖然也是定長，但是有兩種長度數據的接收，所以還是從設計接收不定長的數據為最終效果。

狀態機的運用

對于不定長數據的接收，使用了狀態機，分兩次中斷來接收數據

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
	if(huart- >Instance == USART6)	                                 // 判斷是由哪個串口觸發的中斷
	{
		if(StateMachine_USART6)                                      //狀態機為1，都接收完畢，準備校驗
		{	
      if(re_flag6 == 1)
			{
				UART6_RxCounter = 6;
				re_flag6 = 0;
			}	
      else
			{
				len_counter6 = 2+5+UART6_RxBuffer[2]+(UART6_RxBuffer[3]< 8);  
			  if(UART6_RxBuffer[len_counter6 - 1] == 0x55 && UART6_RxBuffer[0] == 0xAA)	
			  {
				  UART6_RxCounter = len_counter6;
			  }	
        else
			  {
				  memset(UART6_RxBuffer,0,0x400);
					UART6_RxCounter = 0;
			  }		
			}				
      		
			StateMachine_USART6 = 0;                                   //狀態機為0
      len_counter6 = 0;			
			HAL_UART_Receive_IT(&huart6,UART6_RxBuffer,5);		
		}
		else                                                         //狀態機為0，只接受到了前五個字節，繼續接收后面的字節
		{					
			if(UART6_RxBuffer[0] == 0xAA)
			{
				StateMachine_USART6 = 1;
				UART6_RxCounter = 5;
				if(UART6_RxBuffer[2] == 0 && UART6_RxBuffer[3] == 0)
			  {
				  HAL_UART_Receive_IT(&huart6,(uint8_t*)&UART6_RxBuffer[5], 1);
					re_flag6 = 1;
			  }
			  else
			    HAL_UART_Receive_IT(&huart6,(uint8_t*)&UART6_RxBuffer[5], 2 + UART6_RxBuffer[2] + (UART6_RxBuffer[3] < < 8));
			}
			else
			{
				memset(UART6_RxBuffer,0,0x400);
				UART6_RxCounter = 0;
				HAL_UART_Receive_IT(&huart6,UART6_RxBuffer,5);
			}
			
		}
	}
}