blink.c

#include <stdio.h>
#include <stdint.h>
#include <signal.h>
#include <time.h>
#include <sys/time.h>
#include <semaphore.h>

#include "gpio.h"
#include "done.h"
#include "blink.h"

#define NANOSECOND 1000000000l

#ifndef TIMESPEC_TO_TIMEVAL
#define TIMESPEC_TO_TIMEVAL(tv, ts) { \
	(tv)->tv_sec = (ts)->tv_sec; \
	(tv)->tv_usec = (ts)->tv_nsec / 1000; \
}
#endif

static sem_t block;

void blink_unblock(int signo) { 
    sem_post(&block); 
}

void *blink_at_frequency(void * _)
{
    enum Direction led1_dir = gpio_get_dir(LED1);
    enum Direction led2_dir = gpio_get_dir(LED2);
    gpio_set_dir(LED1, OUT);
    gpio_set_dir(LED2, OUT);
    gpio_set_value(LED1, OFF);
    gpio_set_value(LED2, OFF);

    int sem_good = 1;
    struct sigaction act; {
        act.sa_handler = blink_unblock;
        act.sa_flags = 0;
        sigfillset(&act.sa_mask);
    }

    if (sem_init(&block, 0, 0) < 0) {
        sem_good = 0;
        perror("Could not initialize semaphore");
        done = 1;
    } else {
        sigaction(SIGALRM, &act, NULL);
    }

    struct timespec sleeptime;
    struct itimerval timeout = {0};
    double duty;

    while (!done) {
        duty = (1.0 / frequency) * NANOSECOND;
        sleeptime.tv_sec = (uint32_t)(duty / NANOSECOND);
        sleeptime.tv_nsec = ((uint64_t)duty) % NANOSECOND;

        enum Value d1 = gpio_get_value(LED1);
        enum Value d1_next = d1 == OFF ? ON : OFF;
        enum Value d2_next = d1 == OFF ? OFF : ON;

        gpio_set_value(LED1, d1_next);
        gpio_set_value(LED2, d2_next);

        TIMESPEC_TO_TIMEVAL(&timeout.it_value, &sleeptime);
        setitimer(ITIMER_REAL, &timeout, NULL);
        sem_wait(&block);
    }

    if (sem_good) {
        sem_destroy(&block);
    }

    gpio_set_value(LED1, OFF);
    gpio_set_value(LED2, OFF);

    gpio_set_dir(LED1, led1_dir);
    gpio_set_dir(LED2, led2_dir);

    return NULL;
}