HAL库——UART的DMA发送（对比接收）

前面讲到的UART接收执行过程：

• 启动UART的DMA接收（这里面还定义了DMA回调函数）：HAL_UART_Receive_DMA
• 接收完成后，请求DMA中断（判断中断的类型）：HAL_DMA_IRQHandler
• 调用DMA接收完成回调函数（同时关闭了DMA接收）：UART_DMAReceiveCplt
• 调用UART接收回调函数（处理数据，启动DMA接收）：HAL_UART_RxCpltCallback

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 UART的DMA发送和接收的过程类似，部分细节不同，DMA的发送执行过程如下：

• 启动UART的DMA发送（其中定义了发送的回调函数）：HAL_UART_Transmit_DMA
• 发送完成，请求DMA中断（判断中断的类型）：HAL_DMA_IRQHandler
• 调用DMA发送完成回调函数：UART_DMATransmitCplt

到这一步还是一样的，执行到 UART_DMATransmitCplt里面时，开始不一样了。看一下UART_DMATransmitCplt说了啥：

static void UART_DMATransmitCplt(DMA_HandleTypeDef *hdma)
{
  UART_HandleTypeDef *huart = (UART_HandleTypeDef *)((DMA_HandleTypeDef *)hdma)->Parent;
  /* DMA Normal mode*/                                //看这里1
  if ((hdma->Instance->CR & DMA_SxCR_CIRC) == 0U)
  {
    huart->TxXferCount = 0x00U;

    /* Disable the DMA transfer for transmit request by setting the DMAT bit
       in the UART CR3 register */
    CLEAR_BIT(huart->Instance->CR3, USART_CR3_DMAT);

    /* Enable the UART Transmit Complete Interrupt */
    SET_BIT(huart->Instance->CR1, USART_CR1_TCIE);

  }
  /* DMA Circular mode */                             //看这里2
  else
  {
#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
    /*Call registered Tx complete callback*/
    huart->TxCpltCallback(huart);
#else
    /*Call legacy weak Tx complete callback*/
    HAL_UART_TxCpltCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */
  }
}

程序不长，看着好像和UART_DMAReceiveCplt没啥区别，不过还是不一样的，说明如下：

• DMA发送的回调函数处理需要区分DMA传输的模式（即区分normal和circular）
• 看这里1：如果DMA配置为normal模式，那么就会置位UART_CR1_TCIE，查用户手册可以知道，这是使能了UART的传送完成中断，生成UART中断，便进入了UART的中断请求，后面再说具体内容
• 看这里2：如果DMA配置为circular模式，那么就和接收模式下的处理过程类似了，如果没有动态配置回调函数，就会直接调用HAL_UART_TxCpltCallback

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那么DMA配置成normal模式，进了UART的中断请求，后面发生了什么那，说明如下：

• 首先进UART的中断请求：HAL_UART_IRQHandler 

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) && ((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 stream */
          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 */

  /* 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);                          //看这里
    return;
  }
}

 和DMA的中断请求一样的套路，根据状态寄存器的值判断中断的种类，不过和DMA中断请求不同的是，UART中断请求没有直接调用回调函数，而是先进对应的中断处理函数。本例发送完成中断便会调用程序最后的UART_EndTransmit_IT。 

• 调用发送完成中断处理函数：UART_EndTransmit_IT

static HAL_StatusTypeDef UART_EndTransmit_IT(UART_HandleTypeDef *huart)
{
  /* Disable the UART Transmit Complete Interrupt */
  __HAL_UART_DISABLE_IT(huart, UART_IT_TC);

  /* Tx process is ended, restore huart->gState to Ready */
  huart->gState = HAL_UART_STATE_READY;

#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
  /*Call registered Tx complete callback*/
  huart->TxCpltCallback(huart);
#else
  /*Call legacy weak Tx complete callback*/
  HAL_UART_TxCpltCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */

  return HAL_OK;
}

 这部分程序很简短，首先是失能了UART的发送完成中断，后面就是熟悉的套路了——UART的回调函数，之后便进入HAL_UART_TxCpltCallback，和上面就类似了，不多说了。

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总结：以上就是UART的DMA发送啦，主要对比了上篇的接收过程，好像把UART的普通中断模式发送也说了~~