/* https://cirosantilli.com/linux-kernel-module-cheat#uio */

#if 1

/* Adapted from: https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt */

#define _XOPEN_SOURCE 700
#include <fcntl.h> /* open */
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h> /* write */

#include <assert.h>
#include <sys/mman.h>

int main(int argc, char **argv) {
    char *dev = "/dev/uio0";
    if (argc > 1) {
        dev = argv[1];
        exit(EXIT_FAILURE);
    }
    int fd = open(dev, O_RDWR);
    if (fd < 0) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    /* TODO not supported by this kernel module? */
#if 0
    int *addr = mmap(NULL, sysconf(_SC_PAGE_SIZE), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (addr == MAP_FAILED) {
        perror("mmap");
        assert(0);
    }
    *addr = 0x12345678;
#endif

    while (1) {
        uint32_t info = 1;
        size_t nb = write(fd, &info, sizeof(info));
        if (nb < sizeof(info)) {
            perror("write");
            close(fd);
            exit(EXIT_FAILURE);
        }
        nb = read(fd, &info, sizeof(info));
        if (nb == sizeof(info)) {
            printf(__FILE__ " read = %u\n", info);
        }
    }
}

#else

/* Ripped from the kernel docs. */

#define _XOPEN_SOURCE 700
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <unistd.h>

int main(void) {
    int uiofd;
    int configfd;
    int err;
    int i;
    unsigned icount;
    unsigned char command_high;

    uiofd = open("/dev/uio0", O_RDONLY);
    if (uiofd < 0) {
        perror("uio open:");
        return errno;
    }
    configfd = open("/sys/class/uio/uio0/device/config", O_RDWR);
    if (configfd < 0) {
        perror("config open:");
        return errno;
    }
    err = pread(configfd, &command_high, 1, 5);
    if (err != 1) {
        perror("command config read:");
        return errno;
    }
    command_high &= ~0x4;
    for(i = 0;; ++i) {
        fprintf(stderr, "Interrupts: %d\n", icount);
        err = pwrite(configfd, &command_high, 1, 5);
        if (err != 1) {
            perror("config write:");
            break;
        }
        err = read(uiofd, &icount, 4);
        if (err != 4) {
            perror("uio read:");
            break;
        }

    }
    return errno;
}

#endif