串口采用DMA方式收发数据有两种不同的方式，第一种方式：采用DMA传输完成中断进行发送和接收；第二种方式：采用串口总线空闲方式收发数据。这两种方式第二种方式更好一些，因为第二种方式可以收发不定长度的数据帧，然而第一种方式不能。但是第二种方式的逻辑复杂一些，收发过程之前都要判断总线是否是空闲。

在此，以USART2的DMA收发方式举例：

一、使用DMA传输完成中断收发

整体思路：上位机发送四个字节的数据，STM32接收完成后进入DMA中断中，发送下位机STM32定义好的数据给上位机并且清除DMA传输完成中断标志位，最后进入发送完成中断，关闭发送通道，清除DMA发送完成标志位。

在上述思路之前，要进行的自然是串口配置、DMA配置以及中断配置。此处的配置函数如下：

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

**函数名称：UpperUsart2Init 

**函数参数：baudRate 波特率 

**函数作用：初始化与上位机通讯的串口Usart2 

**硬件引脚：TX--PD5  RX--PD6  

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

void UpperUsart2Init(int baudRate)  

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

**函数名称：UpperUsart2Init 

**函数参数：baudRate 波特率 

**函数作用：初始化与上位机通讯的串口Usart2 

**硬件引脚：TX--PD5  RX--PD6  

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

void UpperUsart2Init(int baudRate)  

{  

//开启串口时钟、DMA时钟以及相应GPIO时钟  

    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)设置成复用推挽输出  

    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)设置成浮空输入  

    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，故采用循环模式  

     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设置 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);    

    //开启串口、DMA和串口总线空闲中断  

    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); //标志位设置为默认值  

    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以及相应中断。（一定要注意开启时钟）

在本程序中STM32发送给上位机的数据为uint8_t data[4] = {0x01,0x03,0x04,0x06};

下面这个中断是DMA接收完成中断，完成功能是：清除接收完成标志位，并且向上位机发送预定义数据。

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

**函数名称：DMA1_Stream5_IRQHandler 

**函数参数：无 

**函数作用：串口2 DMA接受完成时发送数据给上位机 

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

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);      

}  

}  

 下面这个中断是DMA传输完成中断，完成功能是：清除发送完成标志位。

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

**函数名称：DMA1_Stream6_IRQHandler 

**函数参数：无 

**函数作用：串口2发送完成时中断入口函数，关闭传输通道并且清除标志 

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

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);  

    }  

}