1. 基本的串口通信程序。先读取内容，再将内容写回串口。

#include     <stdio.h>
#include     <stdlib.h> 
#include     <unistd.h>  
#include     <sys/types.h>
#include     <sys/stat.h>
#include     <fcntl.h> 
#include     <termios.h>
#include     <errno.h>
   
main()
{
    int fd;
    int i;
    int len;
    int n = 0;      
    char read_buf[256];
    char write_buf[256];
    struct termios opt; 
    
    fd = open("/dev/ttyATH0", O_RDWR|O_NOCTTY|O_NDELAY);
    if(fd == -1)
    {
        perror("open serial 0\n");
        exit(0);
    }

    tcgetattr(fd, &opt);      
	bzero(&opt, sizeof(opt));
    
	tcflush(fd, TCIOFLUSH);

	cfsetispeed(&opt, B115200);
    cfsetospeed(&opt, B115200);
    
    opt.c_cflag &= ~CSIZE;  
    opt.c_cflag |= CS8;   
    opt.c_cflag &= ~CSTOPB; 
    opt.c_cflag &= ~PARENB; 
    opt.c_cflag &= ~CRTSCTS;
    opt.c_cflag |= (CLOCAL | CREAD);
 
    opt.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
 
    opt.c_oflag &= ~OPOST;
    
    opt.c_cc[VTIME] = 0;
    opt.c_cc[VMIN] = 0;
    
    tcflush(fd, TCIOFLUSH);
 
    printf("configure complete\n");
	
    if(tcsetattr(fd, TCSANOW, &opt) != 0)
    {
        perror("serial error");
        return -1;
    }

    printf("start send and receive data\n");

	while(1)
    {    
        n = 0;
        len = 0;
        bzero(read_buf, sizeof(read_buf)); 
        bzero(write_buf, sizeof(write_buf));
 
        while( (n = read(fd, read_buf, sizeof(read_buf))) > 0 )
        {
            for(i = len; i < (len + n); i++)
            {
                write_buf[i] = read_buf[i - len];
            }
            len += n;
        }
        write_buf[len] = '\0';
              
        printf("Len %d \n", len);
        printf("%s \n", write_buf);
 
        n = write(fd, write_buf, len);
        printf("write %d chars\n",n);
        
        sleep(2);
    }
	
}

2. 注意

    opt.c_cc[VTIME] = 0;
    opt.c_cc[VMIN] = 0;

在这两个值均为0 的情况下，read不管有没有数据都会立即返回。详细情况在linux下man tcsetattr.

如果不设定这两个值，那么read只有收到回车后才会读取缓存中的数据。

程序大部分转载自：http://www.cnblogs.com/lovemo1314/archive/2010/10/29/1864327.html

该链接的程序部分有误。