#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>

int main(int argc, char *argv[])
{
    char *dev_mem = "/dev/mem";

    int fd = open(dev_mem, O_RDWR | O_SYNC);
    if (fd == -1) {
	fprintf(stderr,
	    "error opening >%s<.\n%s\n",
	    dev_mem, strerror(errno));
	exit(1);
    }

    uint32_t cmv_base = 0x80000000;
    uint32_t cmv_size = 0x00001000;
    uint32_t cmv_addr = 0x00000000;

    void *cmvb = mmap((void *)cmv_addr, cmv_size,
	PROT_READ | PROT_WRITE, MAP_SHARED,
	fd, cmv_base);
    if (cmvb == (void *)-1) {
	fprintf(stderr,
	    "error mapping 0x%08lX+0x%08lX @0x%08lX.\n%s\n",
	    (long)cmv_base, (long)cmv_size, (long)cmv_addr,
	    strerror(errno));
	exit(2);
    } else
	cmv_addr = (uint32_t)cmvb;

    uint32_t volatile * volatile cmv = cmvb;

    fprintf(stderr,
	"mapped 0x%08lX+0x%08lX to 0x%08lX.\n",
	(long unsigned)cmv_base, (long unsigned)cmv_size,
	(long unsigned)cmv_addr);

    uint32_t cnt = 0;

    while (1) { /* some condition here */
	uint32_t val = cmv[127];
	if (!(++cnt & 0xFFFF)) {
	    printf("%08X %d\r", cnt, val);
	    fflush(stdout);
	}
    }

    exit(EXIT_SUCCESS);
}