一、前言

        使用DMA通信的好处是，不占用单片机资源（不像普通串口中断，发送一个字节触发一次中断，发送100个字节触发100次中断；接收一个字节触发一次中断，接收200个字节触发200次中断），数据接收完毕触发一次DMA中断；发送数据完毕触发一次DMA中断。

        下图是STM32F103单片机DMA通道关系图。

从上表可以观察到，串口使用DMA的对应关系如下：

                  USART1-RX使用DMA1的channel5

                USART1-TX使用DMA1的channel4

                USART2-RX使用DMA1的channel6

                USART2-TX使用DMA1的channel7

                USART3-RX使用DMA1的channel3

                USART3-TX使用DMA1的channel2

                UART4-RX使用DMA2的channel3

                UART4-TX使用DMA2的channel5

#define UART4_DMA_RX_BUFFER_MAX_LENGTH		(255)
#define UART4_DMA_TX_BUFFER_MAX_LENGTH		(255)
uint8_t UART4_DMA_RX_Buffer[UART4_DMA_RX_BUFFER_MAX_LENGTH];
uint8_t UART4_DMA_TX_Buffer[UART4_DMA_TX_BUFFER_MAX_LENGTH];

 1、UART4  TX DMA初始化程序

void UART4_DMA_Tx_Configuration(void)
{DMA_InitTypeDef  DMA_InitStructure;RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA2 , ENABLE);						//DMA2时钟使能DMA_DeInit(DMA2_Channel5);DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&UART4->DR;		//DMA外设地址DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)UART4_DMA_TX_Buffer;	//发送缓存指针DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;						//传输方向DMA_InitStructure.DMA_BufferSize = UART4_DMA_TX_BUFFER_MAX_LENGTH;		//传输长度DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;		//外设递增DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable; 				//内存递增DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;	//外设数据宽度：BYTEDMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;			//内存数据宽度：BYTEDMA_InitStructure.DMA_Mode = DMA_Mode_Normal;							//循环模式：否//（注：DMA_Mode_Normal为正常模式，DMA_Mode_Circular为循环模式）DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh; 				//优先级：高DMA_InitStructure.DMA_M2M = DMA_M2M_Disable; 							//内存：内存（都）DMA_Init(DMA2_Channel5 , &DMA_InitStructure);							//初始化DMA2_Channel5DMA_ClearFlag(DMA2_FLAG_GL5);DMA_Cmd(DMA2_Channel5 , DISABLE); 										//开启DMA传输
}

2、UART4  RX DMA初始化程序

void UART4_DMA_Rx_Configuration(void)
{DMA_InitTypeDef  DMA_InitStructure;RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA2 , ENABLE);						//DMA2时钟使能DMA_DeInit(DMA2_Channel3);  		DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)(&UART4->DR);DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)UART4_DMA_RX_Buffer;	//接收缓存指针DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;                    DMA_InitStructure.DMA_BufferSize = UART4_DMA_RX_BUFFER_MAX_LENGTH;		//缓冲大小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;							//（注：DMA_Mode_Normal为正常模式，DMA_Mode_Circular为循环模式）                           DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;               DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;                           DMA_Init(DMA2_Channel3, &DMA_InitStructure);            DMA_ClearFlag(DMA2_FLAG_GL3);                              DMA_Cmd(DMA2_Channel3 , ENABLE);  
}

3、UART  启动DMA发送初始化程序

void UART4_DMA_Begin_Send(uint8_t *send_buffer , uint16_t nSendBytes)
{		if (nSendBytes < UART4_DMA_TX_BUFFER_MAX_LENGTH){memcpy(UART4_DMA_TX_Buffer , send_buffer , nSendBytes);DMA_Cmd(DMA2_Channel5 , DISABLE);                    				//关闭DMA传输DMA_SetCurrDataCounter(DMA2_Channel5 , nSendBytes);  				//数据传输量DMA_Cmd(DMA2_Channel5 , ENABLE);               						//开启DMA传输}
}

4、UART4  DMA方式端口初始化程序（包含DMA配置）

//
//DMA中断方式
//
void UART4_Configuration(void)
{GPIO_InitTypeDef GPIO_InitStructure;USART_InitTypeDef USART_InitStructure;// config USART4 clock RCC_APB1PeriphClockCmd(RCC_APB2Periph_GPIOC | RCC_APB1Periph_UART4, ENABLE);// Configure USART4 Tx (PC.10) as alternate function push-pull GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;GPIO_Init(GPIOC, &GPIO_InitStructure);    				//	PC.10// Configure USART4 Rx (PC.11) as input floating GPIO_InitStructure.GPIO_Pin = GPIO_Pin_11;GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;GPIO_Init(GPIOC, &GPIO_InitStructure);					//	PC.11// USART4 mode configUSART_InitStructure.USART_BaudRate = 115200;USART_InitStructure.USART_WordLength = USART_WordLength_8b;USART_InitStructure.USART_StopBits = USART_StopBits_1;USART_InitStructure.USART_Parity = USART_Parity_No ;USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;USART_Init(UART4, &USART_InitStructure);//CPU的小缺陷：串口配置好，如果直接Send，则第1个字节发送不出去如下语句解决第1个字节无法正确发送出去的问题//USART_ClearFlag(UART4, USART_FLAG_TC);     				//清发送完成标志，Transmission Complete flag  	//USART_ITConfig(UART4, USART_IT_RXNE, ENABLE);//USART_Cmd(UART4, ENABLE);USART_Cmd(UART4, ENABLE);USART_ClearFlag(UART4, USART_FLAG_TC); //清除发送完成标志	while (USART_GetFlagStatus(UART4, USART_FLAG_TC) == RESET);//等待空闲帧发送完成后再清零发送完成标志（警告：如果不使能USART_Mode_Tx，会导致单片机在这里死机）USART_ClearFlag(UART4, USART_FLAG_TC);	//清除发送完成标志USART_ITConfig(UART4, USART_IT_RXNE, DISABLE);USART_ITConfig(UART4, USART_IT_TXE, DISABLE);USART_ITConfig(UART4, USART_IT_IDLE, ENABLE);USART_ITConfig(UART4, USART_IT_TC, ENABLE);USART_DMACmd(UART4 ,  USART_DMAReq_Tx,ENABLE);USART_DMACmd(UART4 ,  USART_DMAReq_Rx,ENABLE);//错误：
//1、以下情况初始化STM32F013VC单片机串口4，则单片机会死机
//	USART_ClearFlag(UART4, USART_FLAG_TC); //清除发送完成标志	
//	while (USART_GetFlagStatus(UART4, USART_FLAG_TC) == RESET);	//等待空闲帧发送完成后再清零发送完成标志（警告：如果不使能USART_Mode_Tx，会导致单片机在这里死机）
//	USART_ClearFlag(UART4, USART_FLAG_TC);	//清除发送完成标志
//	USART_Cmd(UART4, ENABLE);
//正确：
//2、以下情况初始化STM32F013VC单片机串口4，则正常运行
//	USART_Cmd(UART4, ENABLE);
//	USART_ClearFlag(UART4, USART_FLAG_TC); //清除发送完成标志	
//	while (USART_GetFlagStatus(UART4, USART_FLAG_TC) == RESET);	//等待空闲帧发送完成后再清零发送完成标志（警告：如果不使能USART_Mode_Tx，会导致单片机在这里死机）
//	USART_ClearFlag(UART4, USART_FLAG_TC);	//清除发送完成标志
//总结：
//3、因此USART_Cmd(UART4, ENABLE);必须放在while (USART_GetFlagStatus(UART4, USART_FLAG_TC) == RESET);前面执行}

5、UART4   DMA中断接收和DMA中断发送

//
//DMA中断方式
//
void UART4_IRQHandler(void)
{uint16_t ch;
//	uint8_t Buffer[10];	//BaseType_t xHigherPriorityTaskWoken = pdFALSE;if (USART_GetITStatus(UART4,USART_IT_IDLE) != RESET){		USART_ClearITPendingBit(UART4 , USART_IT_IDLE);	//必须先清除总线空闲中断标识，然后读一下数据寄存器，DMA接收才会正确（先读SR，然后读DR才能清除空闲中断标识）注意：这句必须要，否则不能够清除中断标志位。ch =  USART_ReceiveData(UART4);					//必须先清除总线空闲中断标识，然后读一下数据寄存器，DMA接收才会正确（先读SR，然后读DR才能清除空闲中断标识）注意：这句必须要，否则不能够清除中断标志位。				//关闭DMA ，防止干扰DMA_Cmd(DMA2_Channel3 , DISABLE); //关闭DMA,防止处理其间有数据//清DMA标志位DMA_ClearFlag(DMA2_FLAG_GL3 | DMA2_FLAG_TC3 | DMA2_FLAG_HT3 | DMA2_FLAG_TE3);//获取接收到的数据长度 单位为字节ch = UART4_DMA_RX_BUFFER_MAX_LENGTH - DMA_GetCurrDataCounter(DMA2_Channel3);if (ch > 0){MB_UART4.Outtime_mark = TRUE;MB_UART4.receCount = ch;memcpy(MB_UART4.mscomm_buffer , UART4_DMA_RX_Buffer , MB_UART4.receCount);//MB_UART4.mscomm_buffer[ch] = '\0';			//自动添加结束符//WriteBufferTo_ringBuffer(GPS_ring , UART4_DMA_RX_Buffer , ch);}//重新赋值计数值，必须大于等于最大可能接收到的数据帧数目DMA_SetCurrDataCounter(DMA2_Channel3 , UART4_DMA_RX_BUFFER_MAX_LENGTH);DMA_Cmd(DMA2_Channel3, ENABLE);//-----------------------------------------------//由于UART4使用DMA通信，所以不需要3.5字符静止时间//-----------------------------------------------//TIM_Cmd(TIM1, DISABLE);//TIM_SetCounter(TIM1, 0x00);//TIM_Cmd(TIM1, ENABLE);//xSemaphoreGiveFromISR(xSemaphoreGPS, &xHigherPriorityTaskWoken);//发送同步信号//如果xHigherPriorityTaskWoken = pdTRUE，那么退出中断后切到当前最高优先级任务执行//portYIELD_FROM_ISR(xHigherPriorityTaskWoken);	//Buffer[0] = 1;//xQueueSendToBackFromISR(xQueue , Buffer , &xHigherPriorityTaskWoken);//portYIELD_FROM_ISR(xHigherPriorityTaskWoken); 		}else if (USART_GetITStatus(UART4,USART_IT_TC)!= RESET) {USART_ClearITPendingBit(UART4, USART_IT_TC);				DMA_ClearFlag(DMA2_FLAG_GL5 | DMA2_FLAG_TC5 | DMA2_FLAG_HT5 | DMA2_FLAG_TE5);DMA_SetCurrDataCounter(DMA2_Channel5 , 0);}	
} 

6、主程序

void main(void)
{UART4_Configuration();UART4_DMA_Tx_Configuration();UART4_DMA_Rx_Configuration();while (1){//在合适的时候调用UART4_DMA_Begin_Send(uint8_t *send_buffer , uint16_t nSendBytes)// 通过DMA中断方式将数据发送出去}
} 

本程序经过多款产品验证OK