// User space program for reading the impulse count and frequency.
// Source: http://linuxdevices.com/articles/AT9847654820.html
//
// Tested from 0 to 270 kHz.
// Enhaced 2005-6 by Rolf Freitag

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

#define FIFO_W "/dev/rtf0"
#define FIFO_R "/dev/rtf1"

int
main ()
{
  int fd1, fd2, r;
  unsigned long long int dat[2];
  const char zero = 0, one = 1;

  mlockall(MCL_CURRENT|MCL_FUTURE);
  fd1 = open (FIFO_W, O_WRONLY);
  fd2 = open (FIFO_R, O_RDONLY);
  assert (fd1 > 2);
  assert (fd2 > 2);

  for (;;)
  {
    write (fd1, &zero, 1);
    r = read (fd2, dat, sizeof (dat[0]));
    assert (r == sizeof (dat[0]));
    write (fd1, &one, 1);
    r = read (fd2, &dat[1], sizeof (dat[0]));
    assert (r == sizeof (dat[0]));
    printf ("Interrupt count = %llu, actual frequency = %llu Hz\n", dat[0], dat[1]);
    sleep (1);
  }
  close (fd1);
  close (fd2);
  return (0);
}