freebsd_pwm.c

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/time.h>

#include <sys/gpio.h>

#define ONE_SECOND 1000000

int gpio_write(int fd, int pin, int value)
{
    int ret;
    struct gpio_req req;

    req.gp_pin = pin;
    req.gp_value = value;
    ret = ioctl(fd, GPIOSET, &req);
    if (ret < 0) {
        perror("ioctl(GPIOSET)");
        exit(2);
    }
    return ret;
}

void plus_usec(struct timeval *timeval, long usec)
{
    timeval->tv_usec += usec;
    while (timeval->tv_usec >= ONE_SECOND) {
        timeval->tv_usec -= ONE_SECOND;
        timeval->tv_sec += 1;
    }
}

int after_now(struct timeval *timeval)
{
    struct timeval now;

    gettimeofday(&now, NULL);
    if (now.tv_sec > timeval->tv_sec) {
        return 1;
    } else if (now.tv_sec == timeval->tv_sec && now.tv_usec > timeval->tv_usec) {
        return 1;
    }
    return 0;
}

long angle_to_pulse_width(int angle)                                                                                              
{
    if (angle < 0 || 180 < angle) {
        perror("0 <= angle <= 180");
        exit(3);
    }
    return 500 + ((int)(angle * 1900 / 180));
}

int main(int argc, char **argv)
{
    int fd;
    int on;
    struct timeval end;
    struct timeval next_cycle;
    struct timeval next_pulse_end;
    long cycle_usec;
    long pulse_width_usec;
    int angle;

    fd = open("/dev/gpioc0", O_RDONLY);
    if (fd < 0) {
        perror("open");
        exit(1);
    }

    angle = 0;
    if (argc > 1) {
        angle = atoi(argv[1]);
    }

    cycle_usec = 20 * 1000;
    pulse_width_usec = angle_to_pulse_width(angle);                                                                               
    gettimeofday(&end, NULL);
    plus_usec(&end, ONE_SECOND / 6);
    gettimeofday(&next_cycle, NULL);
    on = 0;
    while (1) {
        if (!on && after_now(&next_cycle)) {
            next_pulse_end = next_cycle;
            plus_usec(&next_pulse_end, pulse_width_usec);
            plus_usec(&next_cycle, cycle_usec);
            gpio_write(fd, 18, 1);
            on = 1;
        } else if (on && after_now(&next_pulse_end)) {
            gpio_write(fd, 18, 0);
            on = 0;
        }
        usleep(1);
        if (after_now(&end)) {
            break;
        }
    }

    close(fd);

    return 0;
}

Makefile

all: freebsd_pwm

freebsd_pwm: freebsd_pwm.o
        clang freebsd_pwm.o -o freebsd_pwm

freebsd_pwm.o: freebsd_pwm.c
        clang -c freebsd_pwm.c

clean:
        rm freebsd_pwm freebsd_pwm.o