#include
#include
#include
#include
#include

/* baudrate settings are defined in , which is included by */
// 波特率的设置定义在 . 包含在 里
#define BAUDRATE B38400      

/* change this definition for the correct port */
// 定义您所需要的串口号
#define MODEMDEVICE "/dev/ttyS1"

#define _POSIX_SOURCE 1 /*POSIX compliant source POSIX系统兼容*/

#define FALSE 0
#define TRUE 1

volatile int STOP=FALSE;

main() {
 int fd,c, res;
 struct termios oldtio,newtio;
 char buf[255];
 /* Open modem device for reading and writing and not as controlling
 tty because we don't want to get killed if linenoise sends CTRL-C.
 开启设备用于读写，但是不要以控制 tty 的模式，因为我们并不希望在发送 Ctrl-C
 后结束此进程
 */
 fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
 if (fd <0) {perror(MODEMDEVICE); exit(-1); }
 tcgetattr(fd,&oldtio); /* save current serial port settings */
           // 储存当前的串口设置
 bzero(&newtio, sizeof(newtio)); /* clear struct for new port settings */
                                      // 清空新的串口设置结构体
 /*
      BAUDRATE: Set bps rate. You could also use cfsetispeed and cfsetospeed.
      CRTSCTS : output hardware flow control (only used if the cable has all
             ecessary lines. See sect. 7 of Serial-HOWTO)
   CS8     : 8n1 (8bit,no parity,1 stopbit)
   CLOCAL  : local connection, no modem contol
   CREAD   : enable receiving characters
   BAUDRATE: 设置串口的传输速率bps, 也可以使用 cfsetispeed 和 cfsetospeed 来设置
   CRTSCTS : 输出硬件流控(只能在具完整线路的缆线下工作，参考 Serial-HOWTO 第七节)
   CS8     : 8n1 (每一帧8比特数据,无奇偶校验位,1 比特停止位)
   CLOCAL  : 本地连接，无调制解调器控制
   CREAD   : 允许接收数据
 */
 newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;

    /*
 IGNPAR  : ignore bytes with parity errors
 ICRNL   : map CR to NL (otherwise a CR input on the other computer will not
        terminate input) otherwise make device raw (no other input processing)
 IGNPAR  : 忽略奇偶校验出错的字节
 ICRNL   : 把 CR 映像成 NL (否则从其它机器传来的 CR 无法终止输入)或者就把设备设
     为 raw 状态（没有额外的输入处理）
 */
 newtio.c_iflag = IGNPAR | ICRNL;
 
 /*
 Raw output.  Raw 模式输出
 */
 newtio.c_oflag = 0;
 
 /*
 ICANON  : enable canonical input
 disable all echo functionality, and don't send signals to calling program
 ICANON : 启动 标准输出， 关闭所有回显echo 功能，不向程序发送信号
 */
 newtio.c_lflag = ICANON;
 
 /*
 initialize all control characters
 default values can be found in /usr/include/termios.h, and
 are given in the comments, but we don't need them here
 初始化所有的控制字符， 默认值可以在 /usr/include/termios.h 找到，
 并且做了注解，不过这里我们并不需要考虑这些
 */
 newtio.c_cc[VINTR]    = 0;     /* Ctrl-c */
 newtio.c_cc[VQUIT]    = 0;     /* Ctrl-/ */
 newtio.c_cc[VERASE]   = 0;     /* del */
 newtio.c_cc[VKILL]    = 0;     /* @ */
 newtio.c_cc[VEOF]     = 4;     /* Ctrl-d */
 newtio.c_cc[VTIME]    = 0;     /* inter-character timer unused */
                                /* 不使用字符间的计时器 */
 newtio.c_cc[VMIN]     = 1;     /* blocking read until 1 character arrives */
                                   /* 阻塞，直到读取到一个字符 */
 newtio.c_cc[VSWTC]    = 0;     /* '/0' */
 newtio.c_cc[VSTART]   = 0;     /* Ctrl-q */
 newtio.c_cc[VSTOP]    = 0;     /* Ctrl-s */
 newtio.c_cc[VSUSP]    = 0;     /* Ctrl-z */
 newtio.c_cc[VEOL]     = 0;     /* '/0' */
 newtio.c_cc[VREPRINT] = 0;     /* Ctrl-r */
 newtio.c_cc[VDISCARD] = 0;     /* Ctrl-u */
 newtio.c_cc[VWERASE]  = 0;     /* Ctrl-w */
 newtio.c_cc[VLNEXT]   = 0;     /* Ctrl-v */
 newtio.c_cc[VEOL2]    = 0;     /* '/0' */
 
 /*
 now clean the modem line and activate the settings for the port
 清空数据线，启动新的串口设置
 */
 tcflush(fd, TCIFLUSH);
 tcsetattr(fd,TCSANOW,&newtio);
 
 /*
 terminal settings done, now handle input
 In this example, inputting a 'z' at the beginning of a line will
 exit the program.
 终端设置完成，现在就可以处理数据了
 在本程序中，在一行的开始输入一个 'z' 会终止该程序
 */
 while (STOP==FALSE) {     /* loop until we have a terminating condition */
         // 循环直到满足终止条件
 /* read blocks program execution until a line terminating character is
 input, even if more than 255 chars are input. If the number
 of characters read is smaller than the number of chars available,
 subsequent reads will return the remaining chars. res will be set
 to the actual number of characters actually read
 即使输入超过 255 个字节，读取的程序段还是会一直等到行结束符出现才会停止。
    如果读到的字符少于应刚获得的字符数，则剩下的字符串会在下一次读取时读到。
 res 用来获得每次真正读到的字节数
 */
 res = read(fd,buf,255);
 buf[res]=0;             /* set end of string, so we can printf */
                           // 设置字符串结束符，从而可以顺利使用 printf
 printf(":%s:%d/n", buf, res);
 if (buf[0]=='z') STOP=TRUE;
 }
 /* restore the old port settings 恢复旧的串口设置 */
 tcsetattr(fd,TCSANOW,&oldtio);
}

#include    
#include      
#include      
#include      
#include     
#include      
      
#define BAUDRATE B38400     
#define MODEMDEVICE "/dev/ttyS1"     

#define _POSIX_SOURCE 1 /* POSIX compliant source */     
#define FALSE 0     
#define TRUE 1     

volatile int STOP=FALSE;
void signal_handler_IO (int status);   /* definition of signal handler */ 
                                     // 定义信号处理程序
int wait_flag=TRUE;                   /* TRUE while no signal received */    
                                    // TRUE 代表没有受到信号，正在等待中  
main()   {       
 int fd,c, res;  
 struct termios oldtio,newtio; 
 struct sigaction saio;        
 /* definition of signal action */      
 // 定义信号处理的结构
 char buf[255];       
 
 /* open the device to be non-blocking (read will return immediatly) */    
 // 是用非阻塞模式打开设备 read 函数立刻返回，不会阻塞   
    fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NONBLOCK);   
    if (fd <0) {perror(MODEMDEVICE); exit(-1); }       
 
 /* install the signal handler before making the device asynchronous */   
    // 在进行设备异步传输前，安装信号处理程序   
    saio.sa_handler = signal_handler_IO;    
 saio.sa_mask = 0; 
 saio.sa_flags = 0;    
 saio.sa_restorer = NULL;   
    sigaction(SIGIO,&saio,NULL);  

 /* allow the process to receive SIGIO */
 // 允许进程接收 SIGIO 信号     
 fcntl(fd, F_SETOWN, getpid());   
    /* Make the file descriptor asynchronous (the manual page says only 
 O_APPEND and O_NONBLOCK, will work with F_SETFL...) */  
 // 设置串口的文件描述符为异步，man上说，只有 O_APPEND 和 O_NONBLOCK 才能使用F_SETFL
 fcntl(fd, F_SETFL, FASYNC);       
 tcgetattr(fd,&oldtio); /* save current port settings */  
 
    /* set new port settings for canonical input processing */  
 // 设置新的串口为标准输入模式     
 newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;     
 newtio.c_iflag = IGNPAR | ICRNL;    
 newtio.c_oflag = 0;     
 newtio.c_lflag = ICANON; 
 newtio.c_cc[VMIN]=1;   
    newtio.c_cc[VTIME]=0;   
    tcflush(fd, TCIFLUSH);    
 tcsetattr(fd,TCSANOW,&newtio);    
 
 /* loop while waiting for input. normally we would do something     
 useful here 循环等待输入，通常我们会在这里做些其它的事情 */
 while (STOP==FALSE) {      
  printf("./n");usleep(100000);       
  /* after receiving SIGIO, wait_flag = FALSE, input is availableand can be read */
  // 在收到 SIGIO 信号后，wait_flag = FALSE, 表示有输入进来，可以读取了
  if (wait_flag==FALSE) {        
   res = read(fd,buf,255);    
   buf[res]=0;       
   printf(":%s:%d/n", buf, res); 
   if (res==1) STOP=TRUE; /* stop loop if only a CR was input */   
   wait_flag = TRUE;      /* wait for new input 等待新的输入*/  
       }     
  }      
 /* restore old port settings */    
 tcsetattr(fd,TCSANOW,&oldtio); 
}           

/***************************************************************************   
 * signal handler. sets wait_flag to FALSE, to indicate above loop that    *
 * characters have been received.                                          *
***************************************************************************/  

// 信号处理函数，设置 wait_flag 为 FALSE, 以告知上面的循环函数串口收到字符了 
void signal_handler_IO (int status)   {  
 printf("received SIGIO signal./n");    
 wait_flag = FALSE; 
}