功能实现背景介绍

本项目中，需要使用STM32的USART6串口与FPGA板（下位机）通信，需要发送和接收数据，有报文应答机制。

使用的报文规则如表格所示

板间报文的通信协议，校验使用的是和校验

U8 TX_CheckSum(U8 *buf, U8 len) //buf为数组，len为数组长度
{ 
    U8 i, ret = 0;
    for(i=0; i< len; i++)
    {
        ret += *(buf++);
    }
     ret = ~ret;
    return ret;
}
U8 RX_CheckSum(U8 *buf, U8 len) //buf为数组，len为数组长度
{ 
    U8 i, ret = 0;
     for(i=0; i< len; i++)
    {
        ret += *(buf++);
    }
    ret = ret;
    return ret+1;
}

发送和接收的报文要满足不定长

HAL库的中断接收函数

如果要直接使用HAL库的中断接收函数，也就是HAL_UART_Receive_IT()函数

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

在使用时，选择串口，选择接收的缓冲区，选择接收长度。

/**
  * @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;
  }
}

这个函数本质上其实不是中断接收函数，只是配置函数，配置开启中断的信息，并且接收多少定长的数据结束本数据接收，串口的中断接收还是在中断中进行。

我们本次的长度虽然也是定长，但是有两种长度数据的接收，所以还是从设计接收不定长的数据为最终效果。

状态机的运用

对于不定长数据的接收，使用了状态机，分两次中断来接收数据

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
	if(huart- >Instance == USART6)	                                 // 判断是由哪个串口触发的中断
	{
		if(StateMachine_USART6)                                      //状态机为1，都接收完毕，准备校验
		{	
      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;                                   //状态机为0
      len_counter6 = 0;			
			HAL_UART_Receive_IT(&huart6,UART6_RxBuffer,5);		
		}
		else                                                         //状态机为0，只接受到了前五个字节，继续接收后面的字节
		{					
			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);
			}
			
		}
	}
}