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


/******************************************************************/

static unsigned char *xdio_start;
static unsigned char *xdio_r0;
static unsigned char *xdio_r1;
static unsigned char *xdio_r2;
static unsigned char *xdio_r3;
static unsigned short *ptr16;

#define TV_ELAPSED_US(x, y)     ((((x).tv_sec - (y).tv_sec) * 1000000) + \
        ((x).tv_usec - (y).tv_usec))

/*********************************************************************/

long calc_dif(long count, long last)
{
  if (last > count)
  {
    // Ok, we rolled over
    return count + 65536 - last;
  }
  else
  {
    return count - last;
  }
}

/*********************************************************************/


/******************************************************************/

int main(int argc, char *argv[]) 
{
  int fd = open("/dev/mem", O_RDWR|O_SYNC);
  //xdio at 0x12c00000-0x12c00003
  xdio_start = (unsigned char *) mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0x12C00000);
  xdio_r0 = (unsigned char *) (xdio_start + 0);
  xdio_r1 = (unsigned char *) (xdio_start + 1);
  xdio_r2 = (unsigned char *) (xdio_start + 2);
  xdio_r3 = (unsigned char *) (xdio_start + 3);

  ptr16 = (unsigned short *) xdio_r2;

  *xdio_r0 = 0x40; // ?? give me the value to write here
  *xdio_r1 = 0x00; // ?? give me the value to write here
/***
  *xdio_r0 = 0x82;
  *xdio_r1 = 0x00;
   for discrete outputs
  *xdio_r0 = 0x00; 
  *xdio_r1 = 0xFF; 
****/

  printf("Wrote, r0 = 0x43, r1 = 0x00\n");
 
  struct timeval now;
  struct timeval last_time;
  gettimeofday(&last_time, NULL);
  unsigned short last_count = *ptr16; 
  while (1)
  {
    sleep(1);
    gettimeofday(&now, NULL);
    unsigned short count16 = *ptr16; 
    int elapsed_time = TV_ELAPSED_US(now, last_time);
    long n_pulses = calc_dif((long) count16, (long) last_count);
    double frequency = ((double) n_pulses) / (((double) elapsed_time) / 1000000);
    unsigned char byte0 = *xdio_r2; 
    unsigned char byte1 = *xdio_r3; 
    printf("--- %02hhx %02hhx %02hhx %02hhx -  %hx %hu  %d %d %0.0lf\n", 
         xdio_r0, *xdio_r1, byte0, byte1, count16, count16, n_pulses, elapsed_time, frequency);
    
    last_count = count16;
    last_time = now;
  }
}

/******************************************************************/