Example Use Case

The following demo program including the complete process of opening a UART device, listening on it, and printing when readable data is detected.

#include <sys/types.h> 
#include <sys/stat.h>
#include <fcntl.h>  /*File control definition*/
#include <termios.h>  /*PPSIX Terminal operating system definition*/
#include <stdio.h>  /*Standard input and output definition*/
#include <unistd.h> /*UNIX standard function definition*/

#define BAUDRATE        115200
#define UART_DEVICE     "/dev/ttyS3"
 
#define FALSE  -1
#define TRUE   0
 
/**
*@brief  Set communication speed for UART
*@param  fd     Type int  Open UART file
*@param  speed  Type int  UART speed
*@return  void
*/
int speed_arr[] = {B115200, B38400, B19200, B9600, B4800, B2400, B1200, B300,
          		   B115200, B38400, B19200, B9600, B4800, B2400, B1200, B300, };
int name_arr[] = {115200, 38400, 19200, 9600, 4800, 2400, 1200,  300, 
		  		  115200, 38400, 19200, 9600, 4800, 2400, 1200,  300, };
void set_speed(int fd, int speed){
  int   i; 
  int   status; 
  struct termios   Opt;
  tcgetattr(fd, &Opt); 
  for ( i= 0;  i < sizeof(speed_arr) / sizeof(int);  i++) { 
    if  (speed == name_arr[i]) {     
      tcflush(fd, TCIOFLUSH);     
      cfsetispeed(&Opt, speed_arr[i]);  
      cfsetospeed(&Opt, speed_arr[i]);   
      status = tcsetattr(fd, TCSANOW, &Opt);  
      if  (status != 0) {        
        perror("tcsetattr fd1");  
        return;     
      }    
      tcflush(fd,TCIOFLUSH);   
    }  
  }
}
 
/**
*@brief   Set data bit, stop bit and parity check bit
*@param  fd     Type  int  OPEN UART file
*@param  databits Type  int data bit   Value 7 or 8
*@param  stopbits Type  int stop bit   Value 1 or 2
*@param  parity  Type  int  parity check Type Value N,E,O,,S
*/
int set_Parity(int fd,int databits,int stopbits,int parity)
{ 
	struct termios options; 
	if  ( tcgetattr( fd,&options)  !=  0) { 
		perror("SetupSerial 1");     
		return(FALSE);  
	}
	options.c_cflag &= ~CSIZE; 
	switch (databits) /*Set dataa bit count*/
	{   
	case 7:		
		options.c_cflag |= CS7; 
		break;
	case 8:     
		options.c_cflag |= CS8;
		break;   
	default:    
		fprintf(stderr,"Unsupported data size\n"); return (FALSE);  
	}
	switch (parity) 
	{   
		case 'n':
		case 'N':    
			options.c_cflag &= ~PARENB;   /* Clear parity enable */
			options.c_iflag &= ~INPCK;     /* Enable parity checking */ 
			break;  
		case 'o':   
		case 'O':     
			options.c_cflag |= (PARODD | PARENB); /* Set as odd parity check*/  
			options.c_iflag |= INPCK;             /* Disable parity check */ 
			break;  
		case 'e':  
		case 'E':   
			options.c_cflag |= PARENB;     /* Enable parity */    
			options.c_cflag &= ~PARODD;   /* Set as even parity check*/     
			options.c_iflag |= INPCK;       /* Disable parity check */
			break;
		case 'S': 
		case 's':  /*as no parity*/   
			options.c_cflag &= ~PARENB;
			options.c_cflag &= ~CSTOPB;break;  
		default:   
			fprintf(stderr,"Unsupported parity\n");    
			return (FALSE);  
		}  
	/* Set stop bit*/  
	switch (stopbits)
	{   
		case 1:    
			options.c_cflag &= ~CSTOPB;  
			break;  
		case 2:    
			options.c_cflag |= CSTOPB;  
		   break;
		default:    
			 fprintf(stderr,"Unsupported stop bits\n");  
			 return (FALSE); 
	} 
	/* Set input parity option */ 
	if (parity != 'n')   
		options.c_iflag |= INPCK; 
	tcflush(fd,TCIFLUSH);
	options.c_cc[VTIME] = 150; /* Set to more than 15 seconds*/   
	options.c_cc[VMIN] = 0; /* Update the options and do it NOW */
	if (tcsetattr(fd,TCSANOW,&options) != 0)   
	{ 
		perror("SetupSerial 3");   
		return (FALSE);  
	} 
	options.c_lflag  &= ~(ICANON | ECHO | ECHOE | ISIG);  /*Input*/
	options.c_oflag  &= ~OPOST;   /*Output*/
	return (TRUE);  
}
 
int main(int argc, char *argv[])
{
 
    int    fd, c=0, res;
    char *dev;
 
    char  buf[256];
 
    printf("Start...\n");
    if (argc == 2)
    	dev = argv[1];
    else 
    	dev = UART_DEVICE;
    fd = open(dev, O_RDWR);
 
    if (fd < 0) {
        perror(UART_DEVICE);
        exit(1);
    }
 
    printf("Open...\n");
	printf("bandrate %d...\n",BAUDRATE);
    set_speed(fd,BAUDRATE);
	if (set_Parity(fd,8,1,'N') == FALSE)  {
		printf("Set Parity Error\n");
		exit (0);
	}
 
    printf("Reading...\n");
    while(1) {
        res = read(fd, buf, 255);
 
        if(res==0)
            continue;
        buf[res]=0;
 
        printf("%s", buf);
        
        if (buf[0] == 0x0d)
        	printf("\n");
	write(fd,buf,res);
        
        if (buf[0] == '@') break;
    }
 
    printf("Close...\n");
    close(fd);
 
    return 0;
}