/* Copyright 2018 Raptor Engineering, LLC
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <time.h>
#include <assert.h>
#include <inttypes.h>

#define GPIO_BASE	0x1e780000
#define GPIO_DATA	0x0
#define GPIO_DIR	0x4

#define GPIO_BANK_MNOP	0x78
#define GPIO_N7_MASK	0x00008000

static void *gpio_reg = NULL;
static int mem_fd = 0;

inline void timespec_diff(struct timespec *start, struct timespec *stop, struct timespec *result) {
	if ((stop->tv_nsec - start->tv_nsec) < 0) {
		result->tv_sec = stop->tv_sec - start->tv_sec - 1;
		result->tv_nsec = stop->tv_nsec - start->tv_nsec + 1000000000;
	}
	else {
		result->tv_sec = stop->tv_sec - start->tv_sec;
		result->tv_nsec = stop->tv_nsec - start->tv_nsec;
	}

	return;
}

void delay_for_interval(uint32_t interval) {
	uint32_t abort_count = 0;
	uint64_t delay_ns = interval * 1000;

	struct timespec start_time = {.tv_sec=0,.tv_nsec=0};
	struct timespec current_time = {.tv_sec=0,.tv_nsec=0};
	struct timespec difference_time = {.tv_sec=0,.tv_nsec=0};

	abort_count = 0;
	while (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time) < 0) {
		abort_count++;
		if (abort_count > 10) {
			return;
		}
	}
	while (1) {
		current_time.tv_sec = 0;
		current_time.tv_nsec = 0;
		if (clock_gettime(CLOCK_MONOTONIC_RAW, &current_time) < 0) {
			continue;
		}
		timespec_diff(&start_time, &current_time, &difference_time);
		if (difference_time.tv_nsec > delay_ns) {
			break;
		}
	}

	if (difference_time.tv_nsec > (delay_ns * 2)) {
		printf("OVERRAN timer (wanted %lld, got %lld, start: %lld.%lld end: %lld.%lld)\n", delay_ns, difference_time.tv_nsec, start_time.tv_sec, start_time.tv_nsec, current_time.tv_sec, current_time.tv_nsec);
	}
}

int main(void) {
	uint32_t run_cycles;
	uint32_t frequency = 1000;
	uint32_t period = 1000000 / frequency;
	uint32_t halfperiod = period / 2;
	uint32_t duration_ms = 100;
	uint32_t num_cycles = (duration_ms * frequency) / 1000;

	// Open physical memory device
	if (!mem_fd) {
		mem_fd = open("/dev/mem", O_RDWR | O_SYNC);
		if (mem_fd < 0) {
			perror("Unable to open /dev/mem");
			exit(1);
		}
	}

	// Map GPIO registers into virtual memory
	gpio_reg = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE, MAP_SHARED, mem_fd, GPIO_BASE);
	if (gpio_reg == MAP_FAILED) {
		perror("Unable to map GPIO register memory");
		exit(-1);
	}

	// Elevate priority
	if (setpriority(PRIO_PROCESS, 0, -20) < 0) {
		perror("Unable to set priority");
		exit(-1);
	}

	// Set GPIO N7 to OUTPUT
	uint32_t *offset = gpio_reg + GPIO_BANK_MNOP + GPIO_DIR;
	*offset |= GPIO_N7_MASK;

	// Set up GPIO N7 access
	offset = gpio_reg + GPIO_BANK_MNOP + GPIO_DATA;
	for (run_cycles = 0; run_cycles < 100; run_cycles++) {
		delay_for_interval(halfperiod);
		*offset |= GPIO_N7_MASK;
		delay_for_interval(halfperiod);
		*offset &= ~GPIO_N7_MASK;
	}

	return 0;
}