举个例子：
1、后台数据->USART1-> USART2->其它设备，其它设备数据->USART2-> USART1->后台，这两个数据过程也可能同时进行。
2、由于硬件的限制，USART1和USART2的传输波特率不一样，比如USART1使用GPRS通信，USART2使用短距离无线通信；或者USART1使用以太网通信，USART2使用485总线通信。


现在我把我实现的过程简单描述一下：
1、 初始化设置：USART1_RX DMA1_ Channel5，USART2_RX DMA1_ Channel6，USART1_TX DMA1_ Channel4，USART2_TX DMA1_ Channel7（具体设置请看程序包）
2、 当数据发送给USART1接收完毕时候会引起USART1的串口总线中断，计算DMA1_ Channel5内存数组剩余容量，得到接收的字符长度。将接收的字符复制给DMA1_ Channel4内存数组，启动DMA1_ Channel4通道传输数据，（传输完成需要关闭。）下一次数据接收可以在启动DMA1_ Channel4时候就开始，不需要等待DMA1_ Channel4数据传输完成。但是上一次DMA1_ Channel4完成之前，不可以将数据复制给DMA1_ Channel4内存数组，会冲掉以前数据。
3、 USART2类同USART1。


源程序：
IO口定义：
void GPIO_Configuration(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
/* 第1步：打开GPIO和USART部件的时钟 */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
/* 第2步：将USART Tx的GPIO配置为推挽复用模式 */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* 第3步：将USART Rx的GPIO配置为浮空输入模式
由于CPU复位后，GPIO缺省都是浮空输入模式，因此下面这个步骤不是必须的
但是，我还是建议加上便于阅读，并且防止其它地方修改了这个口线的设置参数
*/
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* 第1步：打开GPIO和USART2部件的时钟 */
//RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);
/* 第2步：将USART2 Tx的GPIO配置为推挽复用模式 */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* 第3步：将USART2 Rx的GPIO配置为浮空输入模式
由于CPU复位后，GPIO缺省都是浮空输入模式，因此下面这个步骤不是必须的
但是，我还是建议加上便于阅读，并且防止其它地方修改了这个口线的设置参数
*/
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/* 第3步已经做了，因此这步可以不做
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
*/
GPIO_Init(GPIOA, &GPIO_InitStructure);
}


串口初始化：
void USART_Configuration(void)
{
USART_InitTypeDef USART_InitStructure;
/* 第4步：配置USART参数
- BaudRate = 115200 baud
- Word Length = 8 Bits
- One Stop Bit
- No parity
- Hardware flow control disabled (RTS and CTS signals)
- Receive and transmit enabled
*/
USART_InitStructure.USART_BaudRate = 19200;
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(USART1, &USART_InitStructure);
//配置USART1空闲中断
USART_ITConfig(USART1, USART_IT_IDLE , ENABLE);
/* 第5步：使能 USART， 配置完毕 */
USART_Cmd(USART1, ENABLE);
/* 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(USART1, USART_FLAG_TC); /* 清发送完成标志，Transmission Complete flag */
USART_InitStructure.USART_BaudRate = 9600;
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(USART2, &USART_InitStructure);
//配置USART2空闲中断
USART_ITConfig(USART2, USART_IT_IDLE , ENABLE);
USART_Cmd(USART2, ENABLE);
/* 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(USART2, USART_FLAG_TC); /* 清发送外城标志，Transmission Complete flag */
}


DMA配置：
void DMA_Configuration(void)
{
DMA_InitTypeDef DMA_InitStructure;
/* DMA clock enable */
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE); //开启DMA1外设时钟
/* DMA1 Channel4 (triggered by USART1 Tx event) Config */
DMA_DeInit(DMA1_Channel4);
DMA_InitStructure.DMA_PeripheralBaseAddr = 0x40013804;
DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)USART1_SEND_DATA;
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
DMA_InitStructure.DMA_BufferSize = 512;
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; //循环模式
DMA_InitStructure.DMA_Priority = DMA_Priority_High;
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
DMA_Init(DMA1_Channel4, &DMA_InitStructure);
DMA_ITConfig(DMA1_Channel4, DMA_IT_TC, ENABLE);
DMA_ITConfig(DMA1_Channel4, DMA_IT_TE, ENABLE);
/* Enable USART1 DMA TX request */
USART_DMACmd(USART1, USART_DMAReq_Tx, ENABLE);
DMA_Cmd(DMA1_Channel4, DISABLE);
/* DMA1 Channel5 (triggered by USART2 Tx event) Config */
DMA_DeInit(DMA1_Channel7);
DMA_InitStructure.DMA_PeripheralBaseAddr = 0x40004404;
DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)USART2_SEND_DATA;
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
DMA_InitStructure.DMA_BufferSize = 512;
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;
DMA_InitStructure.DMA_Priority = DMA_Priority_High;
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
DMA_Init(DMA1_Channel7, &DMA_InitStructure);
DMA_ITConfig(DMA1_Channel7, DMA_IT_TC, ENABLE);
DMA_ITConfig(DMA1_Channel7, DMA_IT_TE, ENABLE);
/* Enable USART1 DMA TX request */
USART_DMACmd(USART2, USART_DMAReq_Tx, ENABLE);
DMA_Cmd(DMA1_Channel7, DISABLE);
/* DMA1 Channel5 (triggered by USART1 Rx event) Config */
DMA_DeInit(DMA1_Channel5);
DMA_InitStructure.DMA_PeripheralBaseAddr = 0x40013804;
DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)USART1_RECEIVE_DATA;
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;
DMA_InitStructure.DMA_BufferSize = 512;
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;
DMA_InitStructure.DMA_Priority = DMA_Priority_High;
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
DMA_Init(DMA1_Channel5, &DMA_InitStructure);
DMA_ITConfig(DMA1_Channel5, DMA_IT_TC, ENABLE);
DMA_ITConfig(DMA1_Channel5, DMA_IT_TE, ENABLE);
/* Enable USART1 DMA RX request */
USART_DMACmd(USART1, USART_DMAReq_Rx, ENABLE);
DMA_Cmd(DMA1_Channel5, ENABLE);
/* DMA1 Channel6 (triggered by USART1 Rx event) Config */
DMA_DeInit(DMA1_Channel6);
DMA_InitStructure.DMA_PeripheralBaseAddr = 0x40004404;
DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)USART2_RECEIVE_DATA;
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;
DMA_InitStructure.DMA_BufferSize = 512;
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;
DMA_InitStructure.DMA_Priority = DMA_Priority_Medium;
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
DMA_Init(DMA1_Channel6, &DMA_InitStructure);
DMA_ITConfig(DMA1_Channel6, DMA_IT_TC, ENABLE);
DMA_ITConfig(DMA1_Channel6, DMA_IT_TE, ENABLE);
/* Enable USART2 DMA RX request */
USART_DMACmd(USART2, USART_DMAReq_Rx, ENABLE);
DMA_Cmd(DMA1_Channel6, ENABLE);
}


中断优先级配置：
void NVIC_Configuration(void)
{
NVIC_InitTypeDef NVIC_InitStructure;
/* Configure one bit for preemption priority */
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);
/* Enable the USART1 Interrupt */
NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
/* Enable the USART2 Interrupt */
NVIC_InitStructure.NVIC_IRQChannel = USART2_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 2;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
//Enable DMA Channel4 Interrupt
NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel4_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
//Enable DMA Channel7 Interrupt
NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel7_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 2;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
/*Enable DMA Channel5 Interrupt */
NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel5_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
/*Enable DMA Channel6 Interrupt */
NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel6_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
}


数组定义，含义如题名：
u8 USART1_SEND_DATA[512];
u8 USART2_SEND_DATA[512];
u8 USART1_RECEIVE_DATA[512];
u8 USART2_RECEIVE_DATA[512];
u8 USART1_TX_Finish=1; // USART1发送完成标志量
u8 USART2_TX_Finish=1; // USART2发送完成标志量


USART1中断服务函数
void USART1_IRQHandler(void)
{
u16 DATA_LEN;
u16 i;
if(USART_GetITStatus(USART1, USART_IT_IDLE) != RESET) //如果为空闲总线中断
{
DMA_Cmd(DMA1_Channel5, DISABLE); //关闭DMA,防止处理其间有数据
//USART_RX_STA = USART1->SR; //先读SR，然后读DR才能清除
//USART_RX_STA = USART1->DR;
DATA_LEN=512-DMA_GetCurrDataCounter(DMA1_Channel5);
if(DATA_LEN > 0)
{
while(USART1_TX_Finish==0) //等待数据传输完成才下一次
{
;
}
//将数据送DMA存储地址
for(i=0; i {
USART1_SEND_DATA=https://www.it610.com/article/USART1_RECEIVE_DATA;
}
//USART用DMA传输替代查询方式发送，克服被高优先级中断而产生丢帧现象。
DMA_Cmd(DMA1_Channel4, DISABLE); //改变datasize前先要禁止通道工作
DMA1_Channel4->CNDTR=DATA_LEN; //DMA1,传输数据量
USART1_TX_Finish=0; //DMA传输开始标志量
DMA_Cmd(DMA1_Channel4, ENABLE);
}
//DMA_Cmd(DMA1_Channel5, DISABLE); //关闭DMA,防止处理其间有数据
DMA_ClearFlag(DMA1_FLAG_GL5 | DMA1_FLAG_TC5 | DMA1_FLAG_TE5 | DMA1_FLAG_HT5); //清标志
DMA1_Channel5->CNDTR = 512; //重装填
DMA_Cmd(DMA1_Channel5, ENABLE); //处理完,重开DMA
//读SR后读DR清除Idle
i = USART1->SR;
i = USART1->DR;
}
if(USART_GetITStatus(USART1, USART_IT_PE | USART_IT_FE | USART_IT_NE) != RESET) //出错
{
USART_ClearITPendingBit(USART1, USART_IT_PE | USART_IT_FE | USART_IT_NE);
}
USART_ClearITPendingBit(USART1, USART_IT_TC);
USART_ClearITPendingBit(USART1, USART_IT_IDLE);
}


USART2中断服务函数
void USART2_IRQHandler(void)
{
u16 DATA_LEN;
u16 i;
if(USART_GetITStatus(USART2, USART_IT_IDLE) != RESET) //如果为空闲总线中断
{
DMA_Cmd(DMA1_Channel6, DISABLE); //关闭DMA,防止处理其间有数据
//USART_RX_STA = USART1->SR; //先读SR，然后读DR才能清除
//USART_RX_STA = USART1->DR;
DATA_LEN=512-DMA_GetCurrDataCounter(DMA1_Channel6);
if(DATA_LEN > 0)
{
while(USART2_TX_Finish==0) //等待数据完成才下一次
{
;
}
//将数据送DMA存储地址
for(i=0; i {
USART2_SEND_DATA=https://www.it610.com/article/USART2_RECEIVE_DATA;
}
//USART用DMA传输替代查询方式发送，克服被高优先级中断而产生丢帧现象。
DMA_Cmd(DMA1_Channel7, DISABLE); //改变datasize前先要禁止通道工作
DMA1_Channel7->CNDTR=DATA_LEN; //DMA1,传输数据量
USART2_TX_Finish=0; //DMA传输开始标志量
DMA_Cmd(DMA1_Channel7, ENABLE);
}
//DMA_Cmd(DMA1_Channel5, DISABLE); //关闭DMA,防止处理其间有数据
DMA_ClearFlag(DMA1_FLAG_GL6 | DMA1_FLAG_TC6 | DMA1_FLAG_TE6 | DMA1_FLAG_HT6); //清标志
DMA1_Channel6->CNDTR = 512; //重装填
DMA_Cmd(DMA1_Channel6, ENABLE); //处理完,重开DMA
//读SR后读DR清除Idle
i = USART2->SR;
i = USART2->DR;
}
if(USART_GetITStatus(USART2, USART_IT_PE | USART_IT_FE | USART_IT_NE) != RESET) //出错
{
USART_ClearITPendingBit(USART2, USART_IT_PE | USART_IT_FE | USART_IT_NE);
}
USART_ClearITPendingBit(USART2, USART_IT_TC);
USART_ClearITPendingBit(USART2, USART_IT_IDLE);
}


DMA1_Channel5中断服务函数
void DMA1_Channel5_IRQHandler(void)
{
DMA_ClearITPendingBit(DMA1_IT_TC5);
DMA_ClearITPendingBit(DMA1_IT_TE5);
DMA_Cmd(DMA1_Channel5, DISABLE); //关闭DMA,防止处理其间有数据
DMA1_Channel5->CNDTR = 580; //重装填
DMA_Cmd(DMA1_Channel5, ENABLE); //处理完,重开DMA
}


DMA1_Channel6中断服务函数
void DMA1_Channel6_IRQHandler(void)
{
DMA_ClearITPendingBit(DMA1_IT_TC6);
DMA_ClearITPendingBit(DMA1_IT_TE6);
DMA_Cmd(DMA1_Channel6, DISABLE); //关闭DMA,防止处理其间有数据
DMA1_Channel6->CNDTR = 580; //重装填
DMA_Cmd(DMA1_Channel6, ENABLE); //处理完,重开DMA
}


DMA1_Channel4中断服务函数
//USART1使用DMA发数据中断服务程序
void DMA1_Channel4_IRQHandler(void)
{
DMA_ClearITPendingBit(DMA1_IT_TC4);
DMA_ClearITPendingBit(DMA1_IT_TE4);
DMA_Cmd(DMA1_Channel4, DISABLE); //关闭DMA
USART1_TX_Finish=1; //置DMA传输完成
}


DMA1_Channel7中断服务函数
//USART2使用DMA发数据中断服务程序
void DMA1_Channel7_IRQHandler(void)
{
DMA_ClearITPendingBit(DMA1_IT_TC7);
DMA_ClearITPendingBit(DMA1_IT_TE7);
DMA_Cmd(DMA1_Channel7, DISABLE); //关闭DMA
USART2_TX_Finish=1; //置DMA传输完成
【stm32的串口空闲中断接收数据】}

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