// send.c .......................................... 
 #include  <stdio.h> 
 #include  <string.h> 
 #include  <sys/types.h> 
 #include  <sys/stat.h> 
 #include  <fcntl.h> 
 #include  <unistd.h> 
 #include  <termios.h> 
 #include  <assert.h> 
 #include  <errno.h> 
 #include  <stdlib.h> 
  
  
 #define TTYS0 /dev/ttyS0 
 #define TTYS1 /dev/ttyS1 
  
  
 #define MAX_BUF_SIZE 1024*20    // define maxinum buffer length 
  
 int open_serial_port(int device) 
 { 
     int serial_port; 
     if (0 == device) 
     { 
         if (serial_port = open("dev/ttyS0",O_RDWR | O_NOCTTY | O_NDELAY)  < 0) 
         { 
             perror("open /dev/ttyS0 encouter an error\n"); 
             exit(1); 
         } 
         printf("open /dev/ttyS0 success.serial_port is %d..\n",serial_port); 
     } 
     else 
     { 
         if (serial_port = open("/dev/ttyS1",O_RDWR | O_NOCTTY | O_NDELAY)  < 0 ) 
         { 
             perror("open /dev/ttyS1 encouter an error\n"); 
             exit(1); 
         } 
         printf("open /dev/ttyS1 success.serial_port is %d..\n",serial_port); 
     } 
     return serial_port; 
 } 
  
  
 int main(int argc,char *argv[]) 
 { 
     char *msg = "hi,everyone..."; 
     int sendlen = strlen(msg); 
     int serial_port = open_serial_port(1);  // open /dev/ttyS0 
     struct termios opt; 
     tcgetattr(serial_port,&opt); 
     cfmakeraw(&opt);// sets the structure specified by opt to raw mode. 
                     // there is no effect on the hardware until a subsequent successful call to tcsetattr()... 
     cfsetispeed(&opt,B38400);   // set input baud as 38400 bps 
     cfsetospeed(&opt,B38400);  
     opt.c_cc[VMIN] = 1; 
     opt.c_cc[VTIME] = 1; 
     tcsetattr(serial_port,TCSANOW,&opt); //change attr as soon as possible 
     while (1) 
     { 
         int ret_val = write(serial_port,msg,sendlen); 
         assert(ret_val != -1); 
         printf("write %d bytes to serial_port %d successfully...\n",ret_val,serial_port); 
         sleep(3); 
     } 
     if (close(serial_port) == -1) 
     { 
         printf("close serial_port error\n"); 
         (1); 
     } 
     printf("leave...\n"); 
     return 0; 
 }