/* parad.c: A very simple linux user space program for the simple one bit ADC via
            the Parallel Port and 8 330 Ohm resitors between every data pin and the
            input.
            See also parda.c.

Parameter: I/O-Address (usually 888 for standard parallel port).

Measured frequency with Linux version 2.6.8-24.11-smp (SuSE 9.2) and the onboard port:
delay with usleep frequency/Hz (onboard port)
10000000          0.05
1000000           0.4988
248000            2.00
100000            4.9
10000             41,6
1000              166
1 ... 100         249,9
0                 499,9
0 without udelay approx. 200 kHz

The same was measured with a parallel port PCI card.

Rolf Freitag Feb. 2005, nobodyo@web.de

*/

#include <stdio.h>
#include <sys/io.h>                               // or asm/io.h; for inb, ioperm, iopl  ...
#include <stdlib.h>                               // atoi
#include <unistd.h>                               // getuid(), usleep
#include <errno.h>                                // EPERM

int
main (int argc, char *argv[])                     /* Caution: A wrong parameter value can cause serious damage! */
{
  int base;                                       // base address of the parallel port
  int value = 0;                                  // bit pattern of the data pins (0 = off, 255 = all high)

  if (2 != argc)
  {
    printf ("Usage: %s <parallel port base>\n", argv[0]);
    exit (-1);
  }
  base = strtol (argv[1],  (char **)NULL, 0);
  if (geteuid () != 0)
  {
    printf ("\a\n\nError: $EUID==%d!=0 (you are not a superuser, port access would be denied from the kernel), exiting.\n\n", getuid ());
    exit (-EPERM);
  }
  iopl (3);                                       // unlimited I/O access permission, nessesary above the 0x3ff limit e. g. at 0x9800=38912

  outb (0x2b, base + 2);                          // read mode
  for (;;)
  {
    value = inb (base);
    printf ("Parallel port data: %d\n", value);
    sleep (1);
  }
  iopl (0);                                       // no I/O permission
  exit (0);
};