RS 232, CentOS 5.6, gcc 3.4.9

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Old 06-24-2011
RS 232, CentOS 5.6, gcc 3.4.9

Can somebody help me with one problem. I write driver for I/o from COM port.
That's the main code:

#include <stdio.h> // standard input / output functions
#include <string.h> // string function definitions
#include <unistd.h> // UNIX standard function definitions
#include <fcntl.h> // File control definitions
#include <errno.h> // Error number definitions
#include <termios.h> // POSIX terminal control definitionss
#include <time.h>   // time calls
#include <sys/ioctl.h>
#include <linux/serial.h>			// Здесь описана serial_icount_struct

int	fd;
int open_port(void)
int	iret;
int	fl_flags;

	fd = open("/dev/ttyS0", O_NONBLOCK | O_RDWR);
	if(fd == -1) // if open is unsucessful
		printf("open_port: Unable to open /dev/ttyS0. \n");
		return -1;
		fl_flags = fcntl(fd,F_GETFL);
		iret = fcntl(fd, F_SETFL, FNDELAY);
//		iret = fcntl(fd, F_SETFL, fl_flags & ~O_NONBLOCK);
		if (iret)
			printf("Error fcntl %s\n", strerror(errno));
		printf("port is open.\n");

	// Переведем устройство в exclusive mode
	iret = ioctl(fd, TIOCEXCL, 0);
	if (iret < 0) {
		return -1;

		return 0;


int configure_port()
int	iret;
	struct termios port_settings;      // structure to store the port settings in
	iret = tcgetattr(fd, &port_settings);
	if (iret) 
		printf("Error tcgetattr %s\n", strerror(errno));
	cfsetispeed(&port_settings, B110);   // set baud rates
	cfsetospeed(&port_settings, B110);
/*	cfsetispeed(&port_settings, B9600);    // set baud rates
	cfsetospeed(&port_settings, B9600);

    	port_settings.c_cflag     &= ~(CSIZE | CSTOPB | PARENB | CLOCAL);
    	port_settings.c_cflag     |= CS8 | CREAD | HUPCL;

    	port_settings.c_iflag      = IGNBRK | IGNPAR;
    	port_settings.c_oflag      = 0;
    	port_settings.c_lflag      = 0;
    	port_settings.c_cc[VMIN]   = 1;
    	port_settings.c_cc[VTIME]  = 10;
	port_settings.c_iflag      = IGNBRK | IGNPAR;
	port_settings.c_oflag      = 0;
	port_settings.c_lflag      = 0;
	port_settings.c_cc[VMIN]   = 1;
	port_settings.c_cc[VTIME]  = 10;

	port_settings.c_cflag &= ~PARENB;    // set no parity, stop bits, data bits

	port_settings.c_cflag &= ~CSTOPB;

	port_settings.c_cflag &= ~CSIZE;

	port_settings.c_cflag |= CS8;
	port_settings.c_cflag |= (CLOCAL | CREAD); 

	iret = tcsetattr(fd, TCSANOW, &port_settings);    // apply the settings to the port

	return 0;

int read_write()

	unsigned char send_bytes[] = {'h','e','l','l','o'};
	char buffer[5];

	int n_write = write(fd, send_bytes, 5);  //Send data
	printf("Wrote the bytes. \n");
	int n_read=read(fd,buffer,1);
	if (n_read == -1)
		printf("Error read %s\n", strerror(errno));

	printf("read %d bytes. \n", n_read);
//	bufptr=buffer;
//	while((n_read=read(fd, bufptr, buffer+sizeof(buffer)-bufptr-1))>0)	
//	bufptr+=n_read;

	return 0;



int main(void)







The problem is - when I return n_read, I get -1 and the error is - Port is temporarily unavaible...

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