【NanoPi NEO/Armbian】PWMでLチカならぬLフワ？

verbosity=1
bootlogo=false
#console=serial
disp_mode=1920x1080p60
overlay_prefix=sun8i-h3
overlays=usbhost1 usbhost2 pwm
rootdev=UUID=4898d57e-5d6d-4c9c-8e8a-96f3009f5fb5
rootfstype=ext4
usbstoragequirks=0x2537:0x1066:u,0x2537:0x1068:u

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

int main()
{
    int fd = -1;
    int ret;
    struct stat st = { 0 };
    unsigned long periodValue;
    unsigned long dutyValue;
    char valueStr[16];
    int strSize;
    const struct timespec tms = { 0U, 22U * 1000U * 1000U };    // 22ms

    // Unexport pwm0 if it exists.
    ret = stat("/sys/class/pwm/pwmchip0/pwm0", &st);
    if(ret == 0) {
        fd = open("/sys/class/pwm/pwmchip0/unexport",O_WRONLY);
        if(write(fd, "0", 1) != 1) {
            perror("write-1");
            exit(EXIT_FAILURE);
        }
        close(fd);
    }

    // Export pwm0.
    fd = open("/sys/class/pwm/pwmchip0/export",O_WRONLY);
    if(write(fd, "0", 1) != 1) {
        perror("write-2");
        exit(EXIT_FAILURE);
    }
    close(fd);

    // Set polarity to normal.
    fd = open("/sys/class/pwm/pwmchip0/pwm0/polarity",O_WRONLY);
    if(write(fd, "normal", 6) != 6) {
        perror("write-3");
        exit(EXIT_FAILURE);
    }
    close(fd);

    // Set period value.
    fd = open("/sys/class/pwm/pwmchip0/pwm0/period",O_RDWR);
    periodValue = 1000000;    // 1kHz
    strSize = snprintf(valueStr ,16, "%lu", periodValue);
    if(write(fd, valueStr, strSize) != strSize) {
        perror("write-4");
        exit(EXIT_FAILURE);
    }
    close(fd);

    // Set initial duty cycle value.
    fd = open("/sys/class/pwm/pwmchip0/pwm0/duty_cycle",O_RDWR);
    dutyValue = 100000;     // 10%
    strSize = snprintf(valueStr, 16, "%lu", dutyValue);
    if(write(fd, valueStr, strSize) != strSize) {
        perror("write-5");
        exit(EXIT_FAILURE);
    }
    close(fd);

    // Set pwm0 enable.
    fd = open("/sys/class/pwm/pwmchip0/pwm0/enable",O_WRONLY);
    if(write(fd, "1", 1) != 1) {
        perror("write-6");
        exit(EXIT_FAILURE);
    }
    close(fd);

    while(1) {
        // duty 10%->100%
        do {
            nanosleep(&tms, NULL);
            //
            fd = open("/sys/class/pwm/pwmchip0/pwm0/duty_cycle",O_RDWR);
            dutyValue += 20000;     // +2%
            strSize = snprintf(valueStr ,16, "%lu", dutyValue);
            if(write(fd, valueStr, strSize) != strSize) {
                perror("write-7");
                exit(EXIT_FAILURE);
            }
            close(fd);
        } while(dutyValue < 1000000);

        // duty 100%->10%
        do {
            nanosleep(&tms, NULL);
            //
            fd = open("/sys/class/pwm/pwmchip0/pwm0/duty_cycle",O_RDWR);
            dutyValue -= 20000;     // -2%
            strSize = snprintf(valueStr, 16, "%lu", dutyValue);
            if(write(fd, valueStr, strSize) != strSize) {
                perror("write-8");
                exit(EXIT_FAILURE);
            }
            close(fd);
        } while(dutyValue > 100000);
    }

    exit(EXIT_SUCCESS);
}