linux 串口通信

串口的操作一般都通过四个步骤来完成：
1、打开串口

2、配置串口：对串口的波特率、数据位、停止位、校验码、等进行设置。

3、读写串口

4、关闭串口

1打开串口：

 #include 
 #include 
 #include 

函数原型： int open(const char *pathname, int flags);
       int open(const char *pathname, int flags, mode_t mode);

int open_port(void)  
{  
    int fd;  
          
    fd=open("/dev/ttyS2",O_RDWR | O_NOCTTY | O_NONBLOCK);//O_NONBLOCK设置为非阻塞模式，在read时不会阻塞住，在读的时候将read放在while循环中
  
    if(fd==-1)  
 {  
	 perror("Can't Open SerialPort");     
    }     
       return fd; 
 }  

可以利用fcntl函数来恢复串口为阻塞状态。

#include 
#include 

fcntl(fd,F_SETFL,0);	//恢复串口阻塞状态，等待串口数据的读入，返回-1代表出错

if(isatty(STDIN_FILENO)==0)
 	printf("isatty success");
	//测试文件描述符是否引用一个终端设备，进一步确认串口是否正确打开。
else
	printf("standard input is not a terminal device\n");

2、配置串口：对串口的波特率、数据位、停止位、校验码、等进行设置。

函数声明：

nt32_t serial_port_open_full(const char *device, uint32_t baud_rate, uint32_t databits, 
 uint32_t stopbits, uint32_t parity, uint32_t flow_ctrl);

kbinfo->tty_fd = serial_port_open_full(tty_dev, 4800, 8, 1, 2, 0);  //函数调用
    
    if (kbinfo->tty_fd  < 0)
    {
        log_error("failed to open %s, %s", tty_dev, strerror(errno));
        exit (1);
    }

int32_t serial_port_open_full(const char *device, uint32_t baud_rate, uint32_t databits,
    uint32_t stopbits, uint32_t parity, uint32_t flow_ctrl)
{
    int32_t comfd;
    struct termios setting;	//

    if (NULL == device)
    {
        log_error("tty device is null");
        return -1;
    }

    if ((comfd = open(device, O_RDWR | O_NOCTTY | O_NONBLOCK)) < 0)
    {
        log_warn("Can not open serial port %s", device);
        return -1;
    }
    
    tcgetattr(comfd, &setting);		//初始化一个终端对应的termios结构

    setting.c_cflag &= ~(CBAUD | CSIZE | CSTOPB | PARENB); //control flag
    setting.c_iflag = 0;    //input flag
    setting.c_oflag = 0;    //output flag
    setting.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); //local flag

    switch (baud_rate)		//波特率
    {
    case 300:
        baud_rate = B300;
        break;
    case 600:
        baud_rate = B600;
        break;
    case 1200:
        baud_rate = B1200;
        break;
    case 2400:
        baud_rate = B2400;
        break;
    case 4800:
        baud_rate = B4800;
        break;
    case 9600:
        baud_rate = B9600;
        break;
    case 19200:
        baud_rate = B19200;
        break;
    case 38400:
        baud_rate = B38400;
        break;
    case 57600:
        baud_rate = B57600;
        break;
    case 115200:
        baud_rate = B115200;
        break;
    case 230400:
        baud_rate = B230400;
        break;
    default:
        log_warn("Invalid baud rate %d.\n", baud_rate);
        goto ERR;
    }

    switch (databits)	//数据位
    {
    case 5:
        databits = CS5;
        break;
    case 6:
        databits = CS6;
        break;
    case 7:
        databits = CS7;
        break;
    case 8:
        databits = CS8;
        break;
    default:
        log_warn("Invalid data bits %d.\n", databits);
        goto ERR;
    }

    switch (stopbits)		//停止位
    {
    case 1:
        stopbits = 0;
        break;
    case 2:
        stopbits = CSTOPB;
        break;
    default:
        log_warn("Invalid stop bits %d.\n", stopbits);
        goto ERR;
    }

    switch (parity)	//校验码
    {
    case 0:
        parity = 0;
        break;
    case 1: //odd
        parity = PARENB|PARODD;
        break;
    case 2: //even
        parity = PARENB;
        break;
    default:
        log_warn("Invalid parity.\n");
        goto ERR;
    }

    switch (flow_ctrl)  //流量控制
    {
    case 0:
        flow_ctrl = 0;
        break;
    case 1: //hardware
        flow_ctrl = CRTSCTS;
        break;
    case 2: //software
        flow_ctrl = 0;
        setting.c_iflag |= (IXON | IXOFF | IXANY);
        break;
    default:
        log_warn("Invalid flow ctrl.\n");
        goto ERR;
    }

    setting.c_cflag |= (baud_rate| databits | stopbits | parity | flow_ctrl | CREAD | CLOCAL);

    cfsetspeed(&setting, baud_rate);
    if (tcsetattr(comfd, TCSAFLUSH, &setting))
    {
        goto ERR;
    }

    return comfd;

ERR:
    close(comfd);
    return -1;
}

最小的termios结构的经典定义如下：

#inlcude
struct termios  
{  
           unsigned char c_iflag;   //输入模式
           unsigned char  c_oflag;  //输出模式
           unsigned char  c_cflag;  //控制模式
           unsigned char  c_lflag;  //本地模式
           unsigned char c_cc[NCC];  //特殊控制模式
}; 

3.读写串口

读串口

#include       
ssize_t read(int fd, void *buf, size_t count);  

nread=read(fd,buff,8);//读串口   
printf("nread=%d,%s\n",nread,buff); 

写串口

#include   
ssize_t write(int fd, const void *buf, size_t count);  

fd:文件描述符

buf:读数据缓存

count:请求读取字节数

4.关闭串口

#include    
int close(int fd);