#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <stdint.h>
#include <unistd.h>

#define	GPIO_REG_MAP            0xFF634000
#define GPIOX_FSEL_REG_OFFSET   0x116
#define GPIOX_OUTP_REG_OFFSET   0x117
#define GPIOX_INP_REG_OFFSET    0x118
#define BLOCK_SIZE              (4*1024)

static volatile uint32_t *gpio;

int main(int argc, char **argv) {
    int fd;

    if ((fd = open("/dev/gpiomem", O_RDWR | O_SYNC | O_CLOEXEC)) < 0) {
        printf("Unable to open /dev/gpiomem\n");
        return -1;
    }

    gpio = mmap(0, BLOCK_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, GPIO_REG_MAP);
    if (gpio < 0) {
        printf("Mmap failed.\n");
        return -1;
    }

    // Print GPIOX FSEL register
    printf("GPIOX_FSEL register : 0x%08x\n",
           *(unsigned int *)(gpio + (GPIOX_FSEL_REG_OFFSET)));

    // Set direction of GPIOX.4 register to out
    *(gpio + (GPIOX_FSEL_REG_OFFSET)) &= ~(1 << 4);
    printf("GPIOX_FSEL register : 0x%08x\n",
           *(unsigned int *)(gpio + (GPIOX_FSEL_REG_OFFSET)));
    // Set GPIOX.4 to high
    *(gpio + (GPIOX_OUTP_REG_OFFSET)) |= (1 << 4);
    printf("GPIOX_INP register : 0x%08x\n",
           *(unsigned int *)(gpio + (GPIOX_INP_REG_OFFSET)));

    usleep(1000000);

    // Set GPIOX.4 to low
    *(gpio + (GPIOX_OUTP_REG_OFFSET)) &= ~(1 << 4);
    printf("GPIOX_INP register : 0x%08x\n",
           *(unsigned int *)(gpio + (GPIOX_INP_REG_OFFSET)));

    return 0;
}