STM32串口通信原理及HAL库代码stm32f1xx

发表于 2023-9-20 14:52

STM32串口通信原理及HAL库代码stm32f1xx_hal_uart.c阅读分析
原理性说明：
//参考网址：https://blog.csdn.net/u010561799/article/details/89526266

在USART的发送端有2个寄存器，一个是程序可以看到的USART_DR寄存器,另一个是程序看不到的移位寄存器,对应USART数据发送有两个标志，一个是TXE=发送数据寄存器空(单字节)，另一个是TC=发送结束(多字节)。

当USART_DR中的1字节数据传送到移位寄存器后，TXE被置位，此时移位寄存器开始向TX信号线按位传输数据，但因为TDR已经变空，程序可以把下一个要发送的1字节数据(操作USART_DR)写入TDR中，而不必等到移位寄存器中所有位(共8位)发送结束，所有多个字节均发送结束时(最后1字节中送出停止位后)硬件会将TC标志置位。

　　另一方面，在刚刚初始化好USART还没有发送任何数据时，也会有TXE标志，因为这时发送数据寄存器是空的(故通常程序串口初始化时不打开此中断，否则频繁进入TXE中断)。而发送完成TCIE和IDLEIE则必须等发送1次数据后，才会有此中断产生，故一开始打开TCIE和IDLEIE中断没有关系。当然一开始必须要打开RXNEIE中断（接收数据），TXEIE和TCIE的意义很简单，TXEIE允许在TXE标志为'1'时产生中断，而TCIE允许在TC标志为'1'时产生中断。

发表于 2023-9-20 14:52

至于什么时候使用哪个标志，需要根据你的需要自己决定。但我认为TXE允许程序有更充裕的时间填写TDR寄存器，保证发送的数据流不间断。TC可以让程序知道发送结束的确切时间，有利于程序控制外部数据流的时序。

TXE--写寄存器DR清零

RXNE--读寄存器DR清零，也可软件手动清零

TC-- 读/写寄存器DR清零，也可软件手动清零

IDLE--需要软件清除，__HAL_UART_CLEAR_IDLEFLAG[HAL]

串口收发数据都是以1个字节为单位，如果是阻塞轮询模式，是while多少字节数，如果是中断，则每收发1个字节，则进入1次中断；

发表于 2023-9-20 14:52

HAL库代码分析：
HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)
{//阻塞串口发送函数
  uint16_t* tmp;
  uint32_t tickstart = 0U;

  /* Check that a Tx process is not already ongoing */
  if(huart->gState == HAL_UART_STATE_READY)
  {
if((pData == NULL) || (Size == 0U))
{
   return  HAL_ERROR;
}

/* Process Locked */
__HAL_LOCK(huart);

huart->ErrorCode = HAL_UART_ERROR_NONE;
huart->gState = HAL_UART_STATE_BUSY_TX;

/* Init tickstart for timeout managment */
tickstart = HAL_GetTick();

huart->TxXferSize = Size;//发送的数据量(多少字节)
huart->TxXferCount = Size;//还剩余的要发送的数据量
while(huart->TxXferCount > 0U)//阻塞模式,while循环
{
   huart->TxXferCount--;//每发完1个字节，剩余要发送数据量减1
   if(huart->Init.WordLength == UART_WORDLENGTH_9B)
   {//带有校验
      if(UART_WaitOnFlagUntilTimeout(huart, UART_FLAG_TXE, RESET, tickstart, Timeout) != HAL_OK)
      {
      return HAL_TIMEOUT;
      }
      tmp = (uint16_t*) pData;
      huart->Instance->DR = (*tmp & (uint16_t)0x01FF);
      if(huart->Init.Parity == UART_PARITY_NONE)
      {//校验正确
      pData +=2U;
      }

发表于 2023-9-20 14:52

else
      {
      pData +=1U;
      }
   }
   else
   {//不带校验
      if(UART_WaitOnFlagUntilTimeout(huart, UART_FLAG_TXE, RESET, tickstart, Timeout) != HAL_OK)
      {//上面函数作用是保证发送寄存器里的数据为空(UART_FLAG_TXE置位)
      return HAL_TIMEOUT;
      }
      huart->Instance->DR = (*pData++ & (uint8_t)0xFF);//发送寄存器写入数据，UART_FLAG_TXE复位【待数据全部移到发送移位寄存器时，UART_FLAG_TXE置位，故前面超时等待】
   }
}

if(UART_WaitOnFlagUntilTimeout(huart, UART_FLAG_TC, RESET, tickstart, Timeout) != HAL_OK)
{//上面函数作用是保证全部传输完成，UART_FLAG_TC置1，否则也认为传输失败，双重保证！
   return HAL_TIMEOUT;
}

/* At end of Tx process, restore huart->gState to Ready */
huart->gState = HAL_UART_STATE_READY;

/* Process Unlocked */
__HAL_UNLOCK(huart);

return HAL_OK;
  }
  else
  {
return HAL_BUSY;
  }
}

发表于 2023-9-20 14:53

HAL_StatusTypeDef HAL_UART_Transmit_IT(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size)
{//串口中断方式发送数据
  /* Check that a Tx process is not already ongoing */
  if(huart->gState == HAL_UART_STATE_READY)
  {
if((pData == NULL) || (Size == 0U))
{
   return HAL_ERROR;
}
/* Process Locked */
__HAL_LOCK(huart);

huart->pTxBuffPtr = pData;//指向待发送缓冲区首地址
huart->TxXferSize = Size;//发送的数据量(多少字节)
huart->TxXferCount = Size;//还剩余的要发送的数据量

huart->ErrorCode = HAL_UART_ERROR_NONE;
huart->gState = HAL_UART_STATE_BUSY_TX;

/* Process Unlocked */
__HAL_UNLOCK(huart);

/* Enable the UART Transmit data register empty Interrupt */
__HAL_UART_ENABLE_IT(huart, UART_IT_TXE);//此处仅仅打开TXE中断，【此时还未开始发送数据，发送缓冲区TDR为空，将进入到串口中断函数-stm32f1xx_it.c的void USARTx_IRQHandler(void) x=1,2,3...】

return HAL_OK;
  }
  else
  {
return HAL_BUSY;
  }
}

发表于 2023-9-20 14:53

void HAL_UART_IRQHandler(UART_HandleTypeDef *huart)
{//串口中断函数回调函数
uint32_t isrflags = READ_REG(huart->Instance->SR);
uint32_t cr1its    = READ_REG(huart->Instance->CR1);
uint32_t cr3its    = READ_REG(huart->Instance->CR3);
uint32_t errorflags = 0x00U;
uint32_t dmarequest = 0x00U;

  /* If no error occurs */
  errorflags = (isrflags & (uint32_t)(USART_SR_PE | USART_SR_FE | USART_SR_ORE | USART_SR_NE));
  if(errorflags == RESET)
  {//无任何串口错误时
/* UART in mode Receiver -------------------------------------------------*/
if(((isrflags & USART_SR_RXNE) != RESET) && ((cr1its & USART_CR1_RXNEIE) != RESET))
{//接收中断标志置位且中断使能
   UART_Receive_IT(huart);//串口中断接收处理函数
   return;
}
  }

发表于 2023-9-20 14:53

/* If some errors occur */
  if((errorflags != RESET) && (((cr3its & USART_CR3_EIE) != RESET) || ((cr1its & (USART_CR1_RXNEIE | USART_CR1_PEIE)) != RESET)))
  {
/* UART parity error interrupt occurred ----------------------------------*/
if(((isrflags & USART_SR_PE) != RESET) && ((cr1its & USART_CR1_PEIE) != RESET))
{//校验出错且校验中断使能
   huart->ErrorCode |= HAL_UART_ERROR_PE;
}

/* UART noise error interrupt occurred -----------------------------------*/
if(((isrflags & USART_SR_NE) != RESET) && ((cr3its & USART_CR3_EIE) != RESET))
{
   huart->ErrorCode |= HAL_UART_ERROR_NE;
}

发表于 2023-9-20 14:53

/* UART frame error interrupt occurred -----------------------------------*/
if(((isrflags & USART_SR_FE) != RESET) && ((cr3its & USART_CR3_EIE) != RESET))
{
   huart->ErrorCode |= HAL_UART_ERROR_FE;
}

/* UART Over-Run interrupt occurred --------------------------------------*/
if(((isrflags & USART_SR_ORE) != RESET) && ((cr3its & USART_CR3_EIE) != RESET))
{
   huart->ErrorCode |= HAL_UART_ERROR_ORE;
}

/* Call UART Error Call back function if need be --------------------------*/
if(huart->ErrorCode != HAL_UART_ERROR_NONE)
{
   /* UART in mode Receiver -----------------------------------------------*/
   if(((isrflags & USART_SR_RXNE) != RESET) && ((cr1its & USART_CR1_RXNEIE) != RESET))
   {
      UART_Receive_IT(huart);
   }

发表于 2023-9-20 14:53

/* If Overrun error occurs, or if any error occurs in DMA mode reception,
      consider error as blocking */
   dmarequest = HAL_IS_BIT_SET(huart->Instance->CR3, USART_CR3_DMAR);
   if(((huart->ErrorCode & HAL_UART_ERROR_ORE) != RESET) || dmarequest)
   {
      /* Blocking error : transfer is aborted
         Set the UART state ready to be able to start again the process,
         Disable Rx Interrupts, and disable Rx DMA request, if ongoing */
      UART_EndRxTransfer(huart);

      /* Disable the UART DMA Rx request if enabled */
      if(HAL_IS_BIT_SET(huart->Instance->CR3, USART_CR3_DMAR))
      {
      CLEAR_BIT(huart->Instance->CR3, USART_CR3_DMAR);

      /* Abort the UART DMA Rx channel */
      if(huart->hdmarx != NULL)
      {
         /* Set the UART DMA Abort callback :
            will lead to call HAL_UART_ErrorCallback() at end of DMA abort procedure */
         huart->hdmarx->XferAbortCallback = UART_DMAAbortOnError;
         if(HAL_DMA_Abort_IT(huart->hdmarx) != HAL_OK)
         {
            /* Call Directly XferAbortCallback function in case of error */
            huart->hdmarx->XferAbortCallback(huart->hdmarx);
         }
      }

发表于 2023-9-20 14:54

  else
      {
         /* Call user error callback */
         HAL_UART_ErrorCallback(huart);//异常回调函数可增加提示
      }
      }
      else
      {
      /* Call user error callback */
      HAL_UART_ErrorCallback(huart);
      }
   }
   else
   {
      /* Non Blocking error : transfer could go on.
         Error is notified to user through user error callback */
      HAL_UART_ErrorCallback(huart);
      huart->ErrorCode = HAL_UART_ERROR_NONE;
   }
}

发表于 2023-9-20 14:54

return;
  } /* End if some error occurs */

  /* UART in mode Transmitter ------------------------------------------------*/
  if(((isrflags & USART_SR_TXE) != RESET) && ((cr1its & USART_CR1_TXEIE) != RESET))
  {//接回上面提到的TXEIE中断被触发，接着执行到此处【每发1个字节执行到此处】，下面有UART_Transmit_IT详细分析
UART_Transmit_IT(huart);
return;
  }

发表于 2023-9-20 14:54

/* UART in mode Transmitter end --------------------------------------------*/
  if(((isrflags & USART_SR_TC) != RESET) && ((cr1its & USART_CR1_TCIE) != RESET))
  {//如果上面的多个字节都发送完毕，则此刻TC标志被置位，如果中断使能，将进入到下面函数执行
UART_EndTransmit_IT(huart);//__HAL_UART_DISABLE_IT(huart, UART_IT_TC);关闭TC中断,还有个回调空白函数-发送完成函数HAL_UART_TxCpltCallback供用户增加想要的功能
return;
  }
}

发表于 2023-9-20 14:55

static HAL_StatusTypeDef UART_Transmit_IT(UART_HandleTypeDef *huart)
{
  uint16_t* tmp;

  /* Check that a Tx process is ongoing */
  if(huart->gState == HAL_UART_STATE_BUSY_TX)
  {
if(huart->Init.WordLength == UART_WORDLENGTH_9B)
{//带有校验处理
   tmp = (uint16_t*) huart->pTxBuffPtr;
   huart->Instance->DR = (uint16_t)(*tmp & (uint16_t)0x01FF);
   if(huart->Init.Parity == UART_PARITY_NONE)
   {
      huart->pTxBuffPtr += 2U;
   }
   else
   {
      huart->pTxBuffPtr += 1U;
   }
}

发表于 2023-9-20 14:55

else
{//不带校验发送
huart->Instance->DR = (uint8_t)(*huart->pTxBuffPtr++ & (uint8_t)0x00FF);//TDR发送寄存器写入数据，TXE标志被清零，待发送寄存器中的1字节数据被全部转移到发送移位寄存器中，此刻发送寄存器又为空，TXE中断再次被触发，由再次进入到串口中断函数，进入到此处执行，故而实现数据连续不间断发送【pTxBuffPtr++指向待发送下1字节数据】
}

发表于 2023-9-20 14:55

if(--huart->TxXferCount == 0U)
{//待发送的字节数为0时，表示数据发送完毕
   /* Disable the UART Transmit Complete Interrupt */
   __HAL_UART_DISABLE_IT(huart, UART_IT_TXE);//必须关闭TXE中断，否则会一直进入，毕竟没数据发送时，TDR一直为空

   /* Enable the UART Transmit Complete Interrupt */
   __HAL_UART_ENABLE_IT(huart, UART_IT_TC);//打开发送完成中断，因为数据发送完毕，TC标志将置位，将再次进入到串口中断函数里执行，此时执行到前面的UART_EndTransmit_IT函数
}
return HAL_OK;
  }
  else
  {
return HAL_BUSY;
  }
}

发表于 2023-9-20 14:55

HAL_StatusTypeDef HAL_UART_Receive(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)
{//串口阻塞接收函数【中断未打开】
  uint16_t* tmp;
  uint32_t tickstart = 0U;

  /* Check that a Rx process is not already ongoing */
  if(huart->RxState == HAL_UART_STATE_READY)
  {
if((pData == NULL) || (Size == 0U))
{
   return  HAL_ERROR;
}

发表于 2023-9-20 14:56

/* Process Locked */
__HAL_LOCK(huart);

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

/* Init tickstart for timeout managment */
tickstart = HAL_GetTick();

huart->RxXferSize = Size;//接收的最大数据量字节数【因是阻塞模式，故事先知道接收多少字节数据】
huart->RxXferCount = Size;//还剩余的要接收的数据量字节数

/* Check the remain data to be received */
while(huart->RxXferCount > 0U)

发表于 2023-9-20 14:56

{
   huart->RxXferCount--;//每接收完1字节，则减1
   if(huart->Init.WordLength == UART_WORDLENGTH_9B)
   {//带有校验
      if(UART_WaitOnFlagUntilTimeout(huart, UART_FLAG_RXNE, RESET, tickstart, Timeout) != HAL_OK)
      {
      return HAL_TIMEOUT;
      }
      tmp = (uint16_t*)pData;
      if(huart->Init.Parity == UART_PARITY_NONE)
      {
      *tmp = (uint16_t)(huart->Instance->DR & (uint16_t)0x01FF);
      pData +=2U;
      }
      else
      {
      *tmp = (uint16_t)(huart->Instance->DR & (uint16_t)0x00FF);
      pData +=1U;
      }

发表于 2023-9-20 14:56

}
   else
   {//不带校验的接收处理
      if(UART_WaitOnFlagUntilTimeout(huart, UART_FLAG_RXNE, RESET, tickstart, Timeout) != HAL_OK)
      {//等待RXNE标志置位，等待时间Timeout【特别说明，如果传递的Size大于实际收到的数据，则肯定会超时】，如果被置位，表示接收寄存器RDR收到数据
      return HAL_TIMEOUT;//如果未被置位，则超时退出
      }
      if(huart->Init.Parity == UART_PARITY_NONE)
      {
      *pData++ = (uint8_t)(huart->Instance->DR & (uint8_t)0x00FF);//从DR读取数据，该操作会将RXNE标志复位，前面置位，故而形成循环，保证数据正确接收
      }

发表于 2023-9-20 14:56

  else
      {
      *pData++ = (uint8_t)(huart->Instance->DR & (uint8_t)0x007F);
      }

   }
}

/* At end of Rx process, restore huart->RxState to Ready */
huart->RxState = HAL_UART_STATE_READY;

/* Process Unlocked */
__HAL_UNLOCK(huart);

return HAL_OK;
  }
  else
  {
return HAL_BUSY;
  }
}

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