Serial Programming Example based on http://xanthium.in/Serial-Port-Programming-on-Linux

serial.c

/* Serial Port Programming
 * Base on the tutorial from
 * http://xanthium.in/Serial-Port-Programming-on-Linux
 */

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

#define BUFFSIZE 100

void settermopt(struct termios *termopt);
void write_serial(int fd, char *buffer);
void read_serial(int fd);

int main(int argc, char *argv[]){
	int fd;
	struct termios termopt;
	char buffer[BUFFSIZE];

	fd = open(argv[1], O_RDWR | O_NOCTTY);

	if(fd == -1){
		fprintf(stderr, "Error opening port: %s\n", argv[1]);
		exit(1);
	}

	fprintf(stdout, "Successfully opened port %s! FD: %d\n", argv[1], fd);

	/* set termios options for tty */
	tcgetattr(fd, &termopt);
	settermopt(&termopt);
	tcsetattr(fd, TCSANOW, &termopt);

	strcpy(buffer, argv[2]);
	write_serial(fd, buffer);

	fprintf(stdout, "Reading...\n\n");
	read_serial(fd);

	close(fd);

	return 0;
}

void settermopt(struct termios *termopt){
	/* Control Option */

	termopt->c_cflag &= ~CRTSCTS;				/* Turn off hardware based flow control */

	termopt->c_cflag |= CREAD | CLOCAL;			/* 
												 * Turn on the receiver(CREAD) and
												 * dont change owner of the port(CLOCAL)
												 */

	termopt->c_cflag &= ~(IXON | IXOFF | IXANY); 	/* Turnoff software based flow control */

	termopt->c_cflag &= ~(ICANON | ECHO | ECHOE | ISIG);	/* Non canonical mode */

	/* Data stream setttings - baud, parity etc */

	cfsetispeed(termopt, B9600);	/* Input baud rate */
	cfsetospeed(termopt, B9600);	/* Output baud rate */

	termopt->c_cflag &= ~PARENB;	/* No Parity */
	termopt->c_cflag &= ~CSTOPB;	/* 1 stop bit */
	termopt->c_cflag &= ~CSIZE;		/* Clear bit Mask for data bits */
	termopt->c_cflag |= CS8;		/* 8 data bit */

	termopt->c_cc[VMIN] = 10;
	termopt->c_cc[VTIME] = 0;
}

void write_serial(int fd, char *buffer){
	int nbytes;

	nbytes = write(fd, buffer, strlen(buffer));

	fprintf(stdout, "%d bytes written!\n", nbytes);
}

void read_serial(int fd){
	char readBuff[BUFFSIZE];
	int nbytes, i;

	tcflush(fd, TCIFLUSH);
	while((nbytes = read(fd, readBuff, BUFFSIZE)) > 0){

		for(i = 0; i < nbytes; i++){
			fprintf(stdout, "%c", readBuff[i]);
		}
	}
	
	fprintf(stdout, "\n");
}