/*
 * Copyright (c) 2022 Marcus Glocker <marcus@nazgul.ch>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <sys/gpio.h>
#include <sys/ioctl.h>

#define PIN_LATCH_MEM	12
#define PIN_CLOCK	23
#define PIN_LATCH	24
#define PIN_DATA	25
#define DELAY 100000000 /* 100ms */
#define LOW 0
#define HIGH 1

int	fd_gpio;

void	usage(void);
void	delay(void);
void	setpin(int, int);
void	shiftbit(int);
void	shiftword(uint16_t);
void	latch_shift(void);
void	latch_mem(void);

void
usage(void)
{
	extern char *__progname;

	printf("usage: %s <binary filename>\n", __progname);

	exit(1);
}

void
delay(void)
{
	struct timespec timeout;

	timeout.tv_nsec = DELAY;
	timeout.tv_sec = 0;
	nanosleep(&timeout, NULL);
}

void
setpin(int pin, int state)
{
	struct gpio_pin_op op;

	memset(&op, 0, sizeof(op));
	op.gp_pin = pin;
	if (state == LOW)
		op.gp_value = GPIO_PIN_LOW;
	else
		op.gp_value = GPIO_PIN_HIGH;
	if (ioctl(fd_gpio, GPIOPINWRITE, &op) == -1)
		err(1, "ioctl");
}

void
shiftbit(int state)
{
	/* make sure clock is low */
	setpin(PIN_CLOCK, LOW);

	/* set data bit */
	if (state == LOW)
		setpin(PIN_DATA, LOW);
	else
		setpin(PIN_DATA, HIGH);

	/* clock in data bit */
	setpin(PIN_CLOCK, HIGH);
	delay();
	setpin(PIN_CLOCK, LOW);
	delay();
}

void
shiftword(uint16_t word)
{
	int i;
	uint8_t bit;

	for (i = 0; i < 16; i++) {
		bit = (word >> i & 1);
		if (bit)
			shiftbit(HIGH);
		else
			shiftbit(LOW);
		//latch_shift();
	}
}

void
latch_shift(void)
{
	setpin(PIN_LATCH, HIGH);
	delay();
	setpin(PIN_LATCH, LOW);
}

void
latch_mem(void)
{
	setpin(PIN_LATCH_MEM, LOW);
	delay();
	setpin(PIN_LATCH_MEM, HIGH);
}

int
main(int argc, char **argv)
{
	uint8_t low;
	uint8_t high;
	uint16_t word;
	int i, n;
	int fd_binary;

	if (argc < 2)
		usage();

	fd_binary = open(argv[1], O_RDONLY);
	if (fd_binary == -1)
		err(1, "open binary");

	fd_gpio = open("/dev/gpio0", O_RDWR);
	if (fd_gpio == -1)
		err(1, "open gpio");

	/* init */
	setpin(PIN_CLOCK, LOW);
	setpin(PIN_DATA, LOW);
	setpin(PIN_LATCH, LOW);
	setpin(PIN_LATCH_MEM, HIGH);

	/* program 8-bit computer */
	for (i = 0; i < 16; i++) {
		low = (uint8_t)i;
		n = read(fd_binary, &high, 1);
		if (n < 1)
			break;
		word = (high << 8 | low);
		printf("Memory Addr %d: Memory value=0x%02x (%d)\n",
		    i, high, high);
		shiftword(word);
		latch_shift();
		latch_mem();
	}

	close(fd_binary);
	close(fd_gpio);

	return 0;
}