前言

最近在實(shí)現(xiàn)利用上位機(jī)通過串口發(fā)送指令給下位機(jī)執(zhí)行操作的實(shí)驗(yàn)，在之前學(xué)習(xí)串口的過程中我就一直有一個(gè)疑惑，那就是為什么在串口中斷回調(diào)函數(shù)內(nèi)除了要加上自己的操作以外還要在末尾再執(zhí)行一次接收中斷，在查閱了一些資料后我才發(fā)現(xiàn)原來和中斷服務(wù)函數(shù)有關(guān)

中斷服務(wù)流程

我們可以從這張圖看出串口收發(fā)數(shù)據(jù)的大致流程：

?串口收發(fā)的寄存器原理

我所使用的F1的串口收發(fā)是通過數(shù)據(jù)寄存器USART_DR來實(shí)現(xiàn)的，其內(nèi)部分為TDR(發(fā)送)和RDR(接收)，當(dāng)向寄存器寫入數(shù)據(jù)時(shí)串口會(huì)自動(dòng)發(fā)送，當(dāng)收到數(shù)據(jù)時(shí)會(huì)將數(shù)據(jù)存入該寄存器，對(duì)應(yīng)到HAL庫的API如下

HAL_StatusTypeDef HAL_UART_Receive(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)
HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout)

當(dāng)我們調(diào)用了中斷服務(wù)入口函數(shù)時(shí)，向函數(shù)傳遞一個(gè)句柄，然后我們就會(huì)跳轉(zhuǎn)到真正的中斷服務(wù)函數(shù)，在這里它會(huì)判斷需要進(jìn)入的是哪種類型的中斷(接收&傳輸)，具體源代碼如下

void HAL_UART_IRQHandler(UART_HandleTypeDef *huart)
{
  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)
  {
    /* UART in mode Receiver -------------------------------------------------*/
    if (((isrflags & USART_SR_RXNE) != RESET) && ((cr1its & USART_CR1_RXNEIE) != RESET))
    {
      UART_Receive_IT(huart);
      return;
    }
  }

  /* 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))
    {
      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;
    }

    /* 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) && (((cr1its & USART_CR1_RXNEIE) != 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);
      }

      /* 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);
            }
          }
          else
          {
            /* Call user error callback */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
            /*Call registered error callback*/
            huart->ErrorCallback(huart);
#else
            /*Call legacy weak error callback*/
            HAL_UART_ErrorCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
          }
        }
        else
        {
          /* Call user error callback */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
          /*Call registered error callback*/
          huart->ErrorCallback(huart);
#else
          /*Call legacy weak error callback*/
          HAL_UART_ErrorCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
        }
      }
      else
      {
        /* Non Blocking error : transfer could go on.
           Error is notified to user through user error callback */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
        /*Call registered error callback*/
        huart->ErrorCallback(huart);
#else
        /*Call legacy weak error callback*/
        HAL_UART_ErrorCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */

        huart->ErrorCode = HAL_UART_ERROR_NONE;
      }
    }
    return;
  } /* End if some error occurs */

  /* Check current reception Mode :
     If Reception till IDLE event has been selected : */
  if (  (huart->ReceptionType == HAL_UART_RECEPTION_TOIDLE)
      &&((isrflags & USART_SR_IDLE) != 0U)
      &&((cr1its & USART_SR_IDLE) != 0U))
  {
    __HAL_UART_CLEAR_IDLEFLAG(huart);

    /* Check if DMA mode is enabled in UART */
    if (HAL_IS_BIT_SET(huart->Instance->CR3, USART_CR3_DMAR))
    {
      /* DMA mode enabled */
      /* Check received length : If all expected data are received, do nothing,
         (DMA cplt callback will be called).
         Otherwise, if at least one data has already been received, IDLE event is to be notified to user */
      uint16_t nb_remaining_rx_data = (uint16_t) __HAL_DMA_GET_COUNTER(huart->hdmarx);
      if (  (nb_remaining_rx_data > 0U)
          &&(nb_remaining_rx_data < huart->RxXferSize))
      {
        /* Reception is not complete */
        huart->RxXferCount = nb_remaining_rx_data;

        /* In Normal mode, end DMA xfer and HAL UART Rx process*/
        if (huart->hdmarx->Init.Mode != DMA_CIRCULAR)
        {
          /* Disable PE and ERR (Frame error, noise error, overrun error) interrupts */
          CLEAR_BIT(huart->Instance->CR1, USART_CR1_PEIE);
          CLEAR_BIT(huart->Instance->CR3, USART_CR3_EIE);

          /* Disable the DMA transfer for the receiver request by resetting the DMAR bit
             in the UART CR3 register */
          CLEAR_BIT(huart->Instance->CR3, USART_CR3_DMAR);

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

          CLEAR_BIT(huart->Instance->CR1, USART_CR1_IDLEIE);

          /* Last bytes received, so no need as the abort is immediate */
          (void)HAL_DMA_Abort(huart->hdmarx);
        }
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
        /*Call registered Rx Event callback*/
        huart->RxEventCallback(huart, (huart->RxXferSize - huart->RxXferCount));
#else
        /*Call legacy weak Rx Event callback*/
        HAL_UARTEx_RxEventCallback(huart, (huart->RxXferSize - huart->RxXferCount));
#endif
      }
      return;
    }
    else
    {
      /* DMA mode not enabled */
      /* Check received length : If all expected data are received, do nothing.
         Otherwise, if at least one data has already been received, IDLE event is to be notified to user */
      uint16_t nb_rx_data = huart->RxXferSize - huart->RxXferCount;
      if (  (huart->RxXferCount > 0U)
          &&(nb_rx_data > 0U) )
      {
        /* Disable the UART Parity Error Interrupt and RXNE interrupts */
        CLEAR_BIT(huart->Instance->CR1, (USART_CR1_RXNEIE | USART_CR1_PEIE));

        /* Disable the UART Error Interrupt: (Frame error, noise error, overrun error) */
        CLEAR_BIT(huart->Instance->CR3, USART_CR3_EIE);

        /* Rx process is completed, restore huart->RxState to Ready */
        huart->RxState = HAL_UART_STATE_READY;
        huart->ReceptionType = HAL_UART_RECEPTION_STANDARD;

        CLEAR_BIT(huart->Instance->CR1, USART_CR1_IDLEIE);
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
        /*Call registered Rx complete callback*/
        huart->RxEventCallback(huart, nb_rx_data);
#else
        /*Call legacy weak Rx Event callback*/
        HAL_UARTEx_RxEventCallback(huart, nb_rx_data);
#endif
      }
      return;
    }
  }

  /* UART in mode Transmitter ------------------------------------------------*/
  if (((isrflags & USART_SR_TXE) != RESET) && ((cr1its & USART_CR1_TXEIE) != RESET))
  {
    UART_Transmit_IT(huart);
    return;
  }

  /* UART in mode Transmitter end --------------------------------------------*/
  if (((isrflags & USART_SR_TC) != RESET) && ((cr1its & USART_CR1_TCIE) != RESET))
  {
    UART_EndTransmit_IT(huart);
    return;
  }
}

我們只需要挑關(guān)鍵的地方來看：在代碼的最開頭定義了幾個(gè)標(biāo)志位，用于判斷是否為接收類型的中斷，如果是的話則調(diào)用接收中斷函數(shù)，代碼如下

static HAL_StatusTypeDef UART_Receive_IT(UART_HandleTypeDef *huart)
{
  uint8_t  *pdata8bits;
  uint16_t *pdata16bits;

  /* Check that a Rx process is ongoing */
  if (huart->RxState == HAL_UART_STATE_BUSY_RX)
  {
    if ((huart->Init.WordLength == UART_WORDLENGTH_9B) && (huart->Init.Parity == UART_PARITY_NONE))
    {
      pdata8bits  = NULL;
      pdata16bits = (uint16_t *) huart->pRxBuffPtr;
      *pdata16bits = (uint16_t)(huart->Instance->DR & (uint16_t)0x01FF);
      huart->pRxBuffPtr += 2U;
    }
    else
    {
      pdata8bits = (uint8_t *) huart->pRxBuffPtr;
      pdata16bits  = NULL;

      if ((huart->Init.WordLength == UART_WORDLENGTH_9B) || ((huart->Init.WordLength == UART_WORDLENGTH_8B) && (huart->Init.Parity == UART_PARITY_NONE)))
      {
        *pdata8bits = (uint8_t)(huart->Instance->DR & (uint8_t)0x00FF);
      }
      else
      {
        *pdata8bits = (uint8_t)(huart->Instance->DR & (uint8_t)0x007F);
      }
      huart->pRxBuffPtr += 1U;
    }

    if (--huart->RxXferCount == 0U)
    {
      /* Disable the UART Data Register not empty Interrupt */
      __HAL_UART_DISABLE_IT(huart, UART_IT_RXNE);

      /* Disable the UART Parity Error Interrupt */
      __HAL_UART_DISABLE_IT(huart, UART_IT_PE);

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

      /* Rx process is completed, restore huart->RxState to Ready */
      huart->RxState = HAL_UART_STATE_READY;

      /* Check current reception Mode :
         If Reception till IDLE event has been selected : */
      if (huart->ReceptionType == HAL_UART_RECEPTION_TOIDLE)
      {
        /* Set reception type to Standard */
        huart->ReceptionType = HAL_UART_RECEPTION_STANDARD;

        /* Disable IDLE interrupt */
        CLEAR_BIT(huart->Instance->CR1, USART_CR1_IDLEIE);

        /* Check if IDLE flag is set */
        if (__HAL_UART_GET_FLAG(huart, UART_FLAG_IDLE))
        {
          /* Clear IDLE flag in ISR */
          __HAL_UART_CLEAR_IDLEFLAG(huart);
        }

#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
        /*Call registered Rx Event callback*/
        huart->RxEventCallback(huart, huart->RxXferSize);
#else
        /*Call legacy weak Rx Event callback*/
        HAL_UARTEx_RxEventCallback(huart, huart->RxXferSize);
#endif
      }
      else
      {
       /* Standard reception API called */
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)		  
       /*Call registered Rx complete callback*/
       huart->RxCpltCallback(huart);
#else
       /*Call legacy weak Rx complete callback*/
       HAL_UART_RxCpltCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
      }

      return HAL_OK;
    }
    return HAL_OK;
  }
  else
  {
    return HAL_BUSY;
  }
}

可以看到這個(gè)函數(shù)的作用是將每次中斷接收到的字符保存在串口的緩存指針中，同時(shí)計(jì)數(shù)器變量自減1，當(dāng)計(jì)數(shù)器為0時(shí)調(diào)用回調(diào)函數(shù)實(shí)現(xiàn)用戶處理邏輯

串口句柄具體定義如下

typedef struct __UART_HandleTypeDef
{
  USART_TypeDef                 *Instance;        /*!< UART registers base address        */

  UART_InitTypeDef              Init;             /*!< UART communication parameters      */

  uint8_t                       *pTxBuffPtr;      /*!< Pointer to UART Tx transfer Buffer */

  uint16_t                      TxXferSize;       /*!< UART Tx Transfer size              */

  __IO uint16_t                 TxXferCount;      /*!< UART Tx Transfer Counter           */

  uint8_t                       *pRxBuffPtr;      /*!< Pointer to UART Rx transfer Buffer */

  uint16_t                      RxXferSize;       /*!< UART Rx Transfer size              */

  __IO uint16_t                 RxXferCount;      /*!< UART Rx Transfer Counter           */

  __IO HAL_UART_RxTypeTypeDef ReceptionType;      /*!< Type of ongoing reception          */

  DMA_HandleTypeDef             *hdmatx;          /*!< UART Tx DMA Handle parameters      */

  DMA_HandleTypeDef             *hdmarx;          /*!< UART Rx DMA Handle parameters      */

  HAL_LockTypeDef               Lock;             /*!< Locking object                     */

  __IO HAL_UART_StateTypeDef    gState;           /*!< UART state information related to global Handle management
                                                       and also related to Tx operations.
                                                       This parameter can be a value of @ref HAL_UART_StateTypeDef */

  __IO HAL_UART_StateTypeDef    RxState;          /*!< UART state information related to Rx operations.
                                                       This parameter can be a value of @ref HAL_UART_StateTypeDef */

  __IO uint32_t                 ErrorCode;        /*!< UART Error code                    */

#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
  void (* TxHalfCpltCallback)(struct __UART_HandleTypeDef *huart);        /*!< UART Tx Half Complete Callback        */
  void (* TxCpltCallback)(struct __UART_HandleTypeDef *huart);            /*!< UART Tx Complete Callback             */
  void (* RxHalfCpltCallback)(struct __UART_HandleTypeDef *huart);        /*!< UART Rx Half Complete Callback        */
  void (* RxCpltCallback)(struct __UART_HandleTypeDef *huart);            /*!< UART Rx Complete Callback             */
  void (* ErrorCallback)(struct __UART_HandleTypeDef *huart);             /*!< UART Error Callback                   */
  void (* AbortCpltCallback)(struct __UART_HandleTypeDef *huart);         /*!< UART Abort Complete Callback          */
  void (* AbortTransmitCpltCallback)(struct __UART_HandleTypeDef *huart); /*!< UART Abort Transmit Complete Callback */
  void (* AbortReceiveCpltCallback)(struct __UART_HandleTypeDef *huart);  /*!< UART Abort Receive Complete Callback  */
  void (* WakeupCallback)(struct __UART_HandleTypeDef *huart);            /*!< UART Wakeup Callback                  */
  void (* RxEventCallback)(struct __UART_HandleTypeDef *huart, uint16_t Pos); /*!< UART Reception Event Callback     */

  void (* MspInitCallback)(struct __UART_HandleTypeDef *huart);           /*!< UART Msp Init callback                */
  void (* MspDeInitCallback)(struct __UART_HandleTypeDef *huart);         /*!< UART Msp DeInit callback              */
#endif  /* USE_HAL_UART_REGISTER_CALLBACKS */

} UART_HandleTypeDef;

因此現(xiàn)在我們可以大致明白為何在回調(diào)函數(shù)內(nèi)還需要再進(jìn)一次中斷了：當(dāng)我們?cè)诨卣{(diào)函數(shù)中調(diào)用

HAL_UART_Receive_IT

其會(huì)跳轉(zhuǎn)到

UART_Start_Receive_IT

更新串口句柄中的具體內(nèi)容，我們緩沖區(qū)的數(shù)據(jù)量也是在這個(gè)時(shí)候被傳入的

而當(dāng)有數(shù)據(jù)傳輸來的時(shí)候，在函數(shù)內(nèi)部就會(huì)對(duì)SR寄存器的位進(jìn)行賦值

?此時(shí)會(huì)產(chǎn)生硬件中斷，進(jìn)入中斷服務(wù)函數(shù)，在服務(wù)函數(shù)內(nèi)部其會(huì)通過前面已經(jīng)寫下的標(biāo)志位判斷到底是要接收還是發(fā)送，而只有當(dāng)真正有數(shù)據(jù)接收到時(shí)接收數(shù)據(jù)標(biāo)志位才會(huì)被賦值，因此在沒有接收到數(shù)據(jù)時(shí)是不會(huì)進(jìn)入中斷的，直到接收到數(shù)據(jù)，然而如果我們不寫這一條語句的話，那么即使我們向串口發(fā)送數(shù)據(jù)，中斷服務(wù)函數(shù)也不會(huì)啟動(dòng)，因?yàn)榇藭r(shí)只有接收數(shù)據(jù)位被賦值。

補(bǔ)充

這里我再補(bǔ)充一下，當(dāng)我們調(diào)用串口接收中斷函數(shù)時(shí)，有可能會(huì)產(chǎn)生發(fā)送數(shù)據(jù)過長(zhǎng)導(dǎo)致終端阻塞的問題，因此我們需要設(shè)置一個(gè)標(biāo)志位重新進(jìn)入中斷

?當(dāng)中斷阻塞時(shí)，timeout就會(huì)被置為1，此時(shí)循環(huán)中的判斷就會(huì)重新再進(jìn)入一次中斷并清除標(biāo)志位直至數(shù)據(jù)全部收完

?文章來源地址http://www.zghlxwxcb.cn/news/detail-693636.html

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