主机:WINXP

开发环境:MDK4.23

MCU:STM32F103CBT6

说明:

串口可以配置成用DMA的方式接收数据,不过DMA需要定长才能产生接收中断,如何接收可变长度的数据呢?

方法有以下3种:

1.将RX脚与一路时钟外部引脚相连,当串口一帧发完,即可利用此定时器产生超时中断.这个实时性较高,可以做到1个字节实时监测.

2.不改变硬件,开启一个定时器监控DMA接收,如果超时则产生中断.这个实时性不高,因为超时时间必须要大于需要接收帧的时间,精度不好控制.

3.STM32单片机有的串口可以监测总线是否处于空闲,如果空闲则产生中断.可以用它来监测DMA接收是否完毕.这种方式实时性很高.

本文采用第3种方式.在波特率576000下大数据包冲击证明可行.

源代码:

//串口接收DMA缓存#define UART_RX_LEN		128extern uint8_t Uart_Rx[UART_RX_LEN];

//串口接收DMA缓存uint8_t Uart_Rx[UART_RX_LEN] = {0};

//---------------------串口功能配置---------------------//打开串口对应的外设时钟  RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 , ENABLE); //串口发DMA配置  //启动DMA时钟RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE);//DMA发送中断设置NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel4_IRQn;NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 3;NVIC_InitStructure.NVIC_IRQChannelSubPriority = 2;NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;NVIC_Init(&NVIC_InitStructure);//DMA1通道4配置DMA_DeInit(DMA1_Channel4);//外设地址DMA_InitStructure.DMA_PeripheralBaseAddr = (u32)(&USART1->DR);//内存地址DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)Uart_Send_Buffer;//dma传输方向单向DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;//设置DMA在传输时缓冲区的长度DMA_InitStructure.DMA_BufferSize = 100;//设置DMA的外设递增模式，一个外设DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;//设置DMA的内存递增模式DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;//外设数据字长DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;//内存数据字长DMA_InitStructure.DMA_MemoryDataSize = DMA_PeripheralDataSize_Byte;//设置DMA的传输模式DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;//设置DMA的优先级别DMA_InitStructure.DMA_Priority = DMA_Priority_High;//设置DMA的2个memory中的变量互相访问DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;DMA_Init(DMA1_Channel4,&DMA_InitStructure);DMA_ITConfig(DMA1_Channel4,DMA_IT_TC,ENABLE);//使能通道4//DMA_Cmd(DMA1_Channel4, ENABLE);//串口收DMA配置  //启动DMA时钟RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE);//DMA1通道5配置DMA_DeInit(DMA1_Channel5);//外设地址DMA_InitStructure.DMA_PeripheralBaseAddr = (u32)(&USART1->DR);//内存地址DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)Uart_Rx;//dma传输方向单向DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;//设置DMA在传输时缓冲区的长度DMA_InitStructure.DMA_BufferSize = UART_RX_LEN;//设置DMA的外设递增模式，一个外设DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;//设置DMA的内存递增模式DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;//外设数据字长DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;//内存数据字长DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;//设置DMA的传输模式DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;//设置DMA的优先级别DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;//设置DMA的2个memory中的变量互相访问DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;DMA_Init(DMA1_Channel5,&DMA_InitStructure);//使能通道5DMA_Cmd(DMA1_Channel5,ENABLE);//初始化参数  //USART_InitStructure.USART_BaudRate = DEFAULT_BAUD;  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_InitStructure.USART_BaudRate = DEFAULT_BAUD; //初始化串口 USART_Init(USART1,&USART_InitStructure);  //TXE发送中断,TC传输完成中断,RXNE接收中断,PE奇偶错误中断,可以是多个   //USART_ITConfig(USART1,USART_IT_RXNE,ENABLE);//中断配置USART_ITConfig(USART1,USART_IT_TC,DISABLE);USART_ITConfig(USART1,USART_IT_RXNE,DISABLE);USART_ITConfig(USART1,USART_IT_IDLE,ENABLE);  //配置UART1中断  NVIC_PriorityGroupConfig(NVIC_PriorityGroup_3);NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;               //通道设置为串口1中断  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;       //中断占先等级0  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;              //中断响应优先级0  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;                 //打开中断  NVIC_Init(&NVIC_InitStructure);   //采用DMA方式发送USART_DMACmd(USART1,USART_DMAReq_Tx,ENABLE);//采用DMA方式接收USART_DMACmd(USART1,USART_DMAReq_Rx,ENABLE);//启动串口  USART_Cmd(USART1, ENABLE); 

//串口1接收中断   void USART1_IRQHandler(void)                               {   uint32_t temp = 0;uint16_t i = 0;if(USART_GetITStatus(USART1, USART_IT_IDLE) != RESET){//USART_ClearFlag(USART1,USART_IT_IDLE);temp = USART1->SR;temp = USART1->DR; //清USART_IT_IDLE标志DMA_Cmd(DMA1_Channel5,DISABLE);temp = UART_RX_LEN - DMA_GetCurrDataCounter(DMA1_Channel5);for (i = 0;i < temp;i++){Data_Receive_Usart = Uart_Rx[i];//启动串口状态机usart_state_run(); }//设置传输数据长度DMA_SetCurrDataCounter(DMA1_Channel5,UART_RX_LEN);//打开DMADMA_Cmd(DMA1_Channel5,ENABLE);} __nop(); } 

测试结果:

条件:单片机运行于72M,与PC通信速率为460800.PC每隔100ms发送一个9个字节的包:c5 5c 6 0 6F 10 5 4e f7.

测试:单片机每次收到此包,一个IO作电平跳转,然后处理返回一包.

示波器显示:

放大显示: