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

int main(int argc, char *argv[]) {

    int fd = open("/sys/bus/pci/devices/0000:17:00.0/resource0", O_RDWR | O_SYNC);
    void* base_address = (void*)0xfbff0000;
    size_t size = 4; 
    void* void_memory = mmap(base_address,
                         size,
                         PROT_READ | PROT_WRITE,
                         MAP_SHARED,
                         fd,
                         0);
    char* memory = (char*)void_memory;

    printf("memory[0] before: %d\n", (int)memory[0]);
    memory[0] = 255;
    sleep(1);
    printf("memory[0] after : %d\n", (int)memory[0]);

}

memory[0] before: 6
memory[0] after : 6