串口采用DMA方式收發數據有兩種不同的方式，第一種方式：采用DMA傳輸完成中斷進行發送和接收；第二種方式：采用串口總線空閑方式收發數據。這兩種方式第二種方式更好一些，因為第二種方式可以收發不定長度的數據幀，然而第一種方式不能。但是第二種方式的邏輯復雜一些，收發過程之前都要判斷總線是否是空閑。

在此，以USART2的DMA收發方式舉例：

一、使用DMA傳輸完成中斷收發

整體思路：上位機發送四個字節的數據，STM32接收完成后進入DMA中斷中，發送下位機STM32定義好的數據給上位機并且清除DMA傳輸完成中斷標志位，最后進入發送完成中斷，關閉發送通道，清除DMA發送完成標志位。

在上述思路之前，要進行的自然是串口配置、DMA配置以及中斷配置。此處的配置函數如下：

/****************************************** 

**函數名稱：UpperUsart2Init 

**函數參數：baudRate 波特率 

**函數作用：初始化與上位機通訊的串口Usart2 

**硬件引腳：TX--PD5  RX--PD6  

******************************************/  

void UpperUsart2Init(int baudRate)  

/****************************************** 

**函數名稱：UpperUsart2Init 

**函數參數：baudRate 波特率 

**函數作用：初始化與上位機通訊的串口Usart2 

**硬件引腳：TX--PD5  RX--PD6  

******************************************/  

void UpperUsart2Init(int baudRate)  

{  

//開啟串口時鐘、DMA時鐘以及相應GPIO時鐘  

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);    

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA1, ENABLE);   

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);    

    GPIO_PinAFConfig(GPIOD,GPIO_PinSource5,GPIO_AF_USART2);  

    GPIO_PinAFConfig(GPIOD,GPIO_PinSource6,GPIO_AF_USART2);   

    //PD8(TX)設置成復用推挽輸出  

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5; //| GPIO_Pin_9;  

    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;  

    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;  

    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;  

    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;  

    GPIO_Init(GPIOD, &GPIO_InitStructure);  

    //PD9(RX)設置成浮空輸入  

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;  

    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;  

    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;  

    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;  

    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;  

    GPIO_Init(GPIOD, &GPIO_InitStructure);    

    // USART2_DMA_RX DMA1_Stream5 DMA_Channel_4   

    DMA_DeInit(DMA1_Stream5);  

    DMA_InitStructure.DMA_Channel = DMA_Channel_4;  

    DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&(USART2->DR);  

    DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)&upperRxBuffer;  

    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;  

    DMA_InitStructure.DMA_BufferSize = UPPERRBSIZE;  

    DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;  

    DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;  

    DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;  

    DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;  

    DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;//如果是Normal只能接受一次，故采用循環模式  

     DMA_InitStructure.DMA_Priority = DMA_Priority_High;  

     DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;           

     DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;  

     DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;  

     DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;  

    DMA_Init(DMA1_Stream5, &DMA_InitStructure);  

    // USART2_DMA_TX DMA1_Stream6 DMA_Channel_4   

    DMA_DeInit(DMA1_Stream6);  

    DMA_InitStructure.DMA_Channel = DMA_Channel_4;  

    DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t) &(USART2->DR);  

    DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)&upperTxBuffer;  

    DMA_InitStructure.DMA_DIR = DMA_DIR_MemoryToPeripheral;  

    DMA_InitStructure.DMA_BufferSize = UPPERTBSIZE;  

    DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;  

    DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;  

    DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;  

    DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;  

    DMA_InitStructure.DMA_Mode =  DMA_Mode_Normal;   //DMA_Mode_Circular;  

    DMA_InitStructure.DMA_Priority = DMA_Priority_High;  

    DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;           

    DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;  

    DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;  

    DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;  

    DMA_Init(DMA1_Stream6, &DMA_InitStructure);  

    //USART2設置 115200 8 1 0 NONE  

    USART_InitStructure.USART_BaudRate = baudRate;  

    USART_InitStructure.USART_WordLength = USART_WordLength_8b;  

    USART_InitStructure.USART_StopBits = USART_StopBits_1;  

    USART_InitStructure.USART_Parity = USART_Parity_No ;  

    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;  

    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;  

    USART_Init(USART2,&USART_InitStructure);  

    // Configure one bit for preemption priority   

    NVIC_PriorityGroupConfig(NVIC_PriorityGroup_0);  

    // Enable DMA1_Stream5 Interrupt   

    NVIC_InitStructure.NVIC_IRQChannel = DMA1_Stream5_IRQn;  

     NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;  

    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 4;  

    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;  

    NVIC_Init(&NVIC_InitStructure);  

    // Enable DMA1_Stream6 Interrupt   

    NVIC_InitStructure.NVIC_IRQChannel = DMA1_Stream6_IRQn;  

    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;  

    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 3;  

    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;  

    NVIC_Init(&NVIC_InitStructure);  

    // Enable USART2 Interrupt   

    NVIC_InitStructure.NVIC_IRQChannel = USART2_IRQn;  

    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;  

    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 5;  

    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;  

    NVIC_Init(&NVIC_InitStructure);    

    //開啟串口、DMA和串口總線空閑中斷  

    DMA_Cmd(DMA1_Stream5,ENABLE);  

    DMA_Cmd(DMA1_Stream6,DISABLE);  

    USART_DMACmd(USART2,USART_DMAReq_Tx,ENABLE);  

    USART_DMACmd(USART2,USART_DMAReq_Rx,ENABLE);    

    DMA_ITConfig(DMA1_Stream5, DMA_IT_TC, ENABLE);  

    DMA_ITConfig(DMA1_Stream6, DMA_IT_TC, ENABLE);  

    DMA_ClearITPendingBit(DMA1_Stream5, DMA_IT_TCIF5); //標志位設置為默認值  

    DMA_ClearITPendingBit(DMA1_Stream6, DMA_IT_TCIF6);        

    USART_ITConfig(USART2,USART_IT_IDLE,ENABLE);   

//  USART_ITConfig(USART2, USART_IT_RXNE, ENABLE);  

    USART_Cmd(USART2, ENABLE);    

}  

上述程序段功能是配置串口、DMA以及相應中斷。（一定要注意開啟時鐘）

在本程序中STM32發送給上位機的數據為uint8_t data[4] = {0x01,0x03,0x04,0x06};

下面這個中斷是DMA接收完成中斷，完成功能是：清除接收完成標志位，并且向上位機發送預定義數據。

/****************************************** 

**函數名稱：DMA1_Stream5_IRQHandler 

**函數參數：無 

**函數作用：串口2 DMA接受完成時發送數據給上位機 

******************************************/  

void DMA1_Stream5_IRQHandler(void)  

{  

if(SET ==  DMA_GetITStatus(DMA1_Stream5, DMA_IT_TCIF5))  

{   

    DMA_Cmd(DMA1_Stream5,DISABLE);  

    DMA_ClearFlag(DMA1_Stream5,DMA_FLAG_TCIF5);  

    DMA_Cmd(DMA1_Stream5,ENABLE);  

    DMA_SetCurrDataCounter(DMA1_Stream6,UPPERTBSIZE);   

    memcpy(upperTxBuffer,data,UPPERTBSIZE);        

    DMA_Cmd(DMA1_Stream6,ENABLE);      

}  

}  

 下面這個中斷是DMA傳輸完成中斷，完成功能是：清除發送完成標志位。

/****************************************** 

**函數名稱：DMA1_Stream6_IRQHandler 

**函數參數：無 

**函數作用：串口2發送完成時中斷入口函數，關閉傳輸通道并且清除標志 

******************************************/  

void DMA1_Stream6_IRQHandler(void) //UART2_TX  

{  

    if(SET == DMA_GetITStatus(DMA1_Stream6,DMA_IT_TCIF6))  

    {  

        DMA_Cmd(DMA1_Stream6,DISABLE);  

        DMA_ClearFlag(DMA1_Stream6, DMA_FLAG_TCIF6);  

    }  

}