Serial programming in C

[oddabd83]

Hi!
I was trying to get my serial port to work by first building a simple program to write and then read data from the same port. The program will keep writing and reading data inside a while loop. However, a problem arises when I tried to put the initialisation of the file descriptors codes outside of the while loop. The serial port will only write and read once, and just blocks there. However, if i place the initialisation codes inside the while loop, and close() the fd whenever I write and read, the problem is gone. Nevertheless I felt that this is very inefficient and there must be something wrong with my codes (or my serial port configurations.)

Here's my codes:

while(1){
	   int fd = open(PIC_BOARD_DEVICE_NAME, O_RDWR | O_NOCTTY | O_NDELAY);
        printf("----------------->PIC board fd: %d\n", fd);
       
	if (fd == -1) {
            printf("CANNOT OPEN FILE DESCRIPTOR.\n");
       
	} else {
            fcntl(fd, F_SETFL, 0); // block serial read and write
	}
	
	// Initialize fd port
	struct termios options;
	
	tcgetattr(fd, &options); // Get the current options for the port.
	cfsetispeed(&options, B2400); // Set the baud rates to B2400.
	cfsetospeed(&options, B2400);
	options.c_cflag |= (CLOCAL | CREAD); // Enable the receiver and set local mode.
	options.c_cflag &= ~PARENB;
	options.c_cflag &= ~CSTOPB;
	options.c_cflag &= ~CSIZE;
	options.c_cflag |= CS8;	
	tcsetattr(fd, TCSANOW, &options); // Set the new options for the port.

	write(fd, &one,1);
	read(fd,&two,1);
	close(fd);
}

[kyku]

Hello, some pointers that you might want to try:
1) What is the reason you do the F_SETFL to 0, I'm not sure if I understand your comment?
2) try using cfmakeraw() on the termios.
3) try memset'ing termios to 0 instead of calling tcgetattr
4) maybe your setup includes control lines, if so enable them (CRTSCTS)
5) for testing purposes don't enable non-blocking mode (O_NDELAY)
6) test the return values of the functions calls: write read tc* if some failed check errno.
7) try setting VTIME and VMIN options