#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <termios.h>
#include <unistd.h>


/*
*    Send NULL bytes to serial port.
*
*    Copyright (C) 2018, 2019 R.J. van der Putten, Leiden, Holland, 
*    rob at sput dot nl.
* 
*    This program is free software; you can redistribute it and/or modify
*    it under the terms of the GNU General Public License version 3 as
*    published by the Free Software Foundation.
* 
*    This program is distributed in the hope that it will be useful,
*    but WITHOUT ANY WARRANTY; without even the implied warranty of
*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*    GNU General Public License for more details.
*/


void hlp(void)
{
	fprintf(stderr, \
		"This program sends null chars to a serial port at 115200 bps.\n");
	fprintf(stderr, "Usage: sndnul -d Device [-t Seconds]\n");
	fprintf(stderr, \
		"Seconds should be 0 ... 10 and defaults to 1.\n");
}


int main(int argc, char **argv)
{
	int fd, i, j, len, opt, secs, wlen;
	struct termios newtio, oldtio;
	char ttysn[256];

	len = 11520;
	char nulchrs[len];

	fd = 0;
	i = 0;
	j = 0;
	opt = 0;
	secs = 1;
	wlen = 0;
	memset(&newtio, 0, sizeof(newtio));
	memset(&oldtio, 0, sizeof(oldtio));
	memset(nulchrs, 0, len);
	memset(ttysn, 0, 256);

        while ((opt = getopt(argc, argv, "d:ht:")) != -1) {
                switch (opt) {
			case 'd':
				strncpy(ttysn, optarg, 255);
				break;
                        case 'h':
                                hlp();
                                exit(0);
			case 't':
				secs = atoi(optarg);
				break;
                        default:
                                hlp();
                                exit(1);
                }
        }
	if (secs < 0 || secs > 10) {
		hlp();
		exit(1);
	}
	if (ttysn[0] == 0 || strncmp(ttysn, "/dev/", 5) != 0) {
		hlp();
		exit(1);
	}

	/*   Open tty   */
	if ((fd = open(ttysn, O_RDWR | O_NOCTTY)) < 0) {
		perror(ttysn);
		exit(1);
	}
	/*  Force blocking IO  */
	fcntl(fd, F_SETFL, 0);

	/*   save current serial port settings   */
	if (tcgetattr(fd, &oldtio) < 0) {
		perror("tcgetattr() failed");
		close(fd);
		exit(1);
	}

	/*
	*   Control flags;
	*   115200 bps, 8 bits, drop DTR when done,
	*   Ignore modem control lines
	*/
	newtio.c_cflag = B115200 | CS8 | HUPCL | CLOCAL;

	/*   Input flags   */
	newtio.c_iflag = IGNPAR;

	/*   Output flags   */
	newtio.c_oflag = 0;

	/*   Local flags   */
	newtio.c_lflag = 0;

	/*   initialise all control characters   */
	newtio.c_cc[VINTR]	= 0;	/* Ctrl-C */
	newtio.c_cc[VQUIT]	= 0;	/* Ctrl-\ */
	newtio.c_cc[VERASE]	= 0;	/* del */
	newtio.c_cc[VKILL]	= 0;	/* Ctrl-U */
	newtio.c_cc[VEOF]	= 0;	/* Ctrl-D */
	newtio.c_cc[VTIME]	= 0;	/* inter-character timer unused */
	newtio.c_cc[VMIN]	= 1;	/* blocking read until 1 character arrives */
	newtio.c_cc[VSWTC]	= 0;	/* '\0' */
	newtio.c_cc[VSTART]	= 0;	/* Ctrl-Q */
	newtio.c_cc[VSTOP]	= 0;	/* Ctrl-S */
	newtio.c_cc[VSUSP]	= 0;	/* Ctrl-Z */
	newtio.c_cc[VEOL]	= 0;	/* '\0' */
	newtio.c_cc[VREPRINT]	= 0;	/* Ctrl-R */
	newtio.c_cc[VDISCARD]	= 0;	/* Ctrl-O */
	newtio.c_cc[VWERASE]	= 0;	/* Ctrl-W */
	newtio.c_cc[VLNEXT]	= 0;	/* Ctrl-V */
	newtio.c_cc[VEOL2]	= 0;	/* '\0' */

	/*   now clean the tty and activate the settings for the port  */
	tcflush(fd, TCIFLUSH);
	tcsetattr(fd, TCSANOW, &newtio);

	/*  Write null chars to serial port  */
	while (secs > 0) {
		i = 0;
		j = len;	/*  Bytes in one second  */
		while (j > 0 && fd > 0) {
			wlen = write(fd, nulchrs + i, j);
			if (j > 0 && wlen < 1 && errno != EINTR) {
				perror("Cant' write to serial port");
				secs = 0;
				break;
			} else {
				i = i + wlen;	/*  Already written  */
				j = len - i;	/*  Still to write   */
			}
		}
		secs--;
	}

	/*   restore the old port settings   */
	tcflush(fd, TCIFLUSH);
	tcsetattr(fd, TCSADRAIN, &oldtio);
	close(fd);

	return(0);
}