9. Example code

Here's a piece of simple example code for I/O port access:

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/*
 * example.c: very simple example of port I/O
 *
 * This code does nothing useful, just a port write, a pause,
 * and a port read. Compile with `gcc -O2 -o example example.c',
 * and run as root with `./example'.
 */

#include <stdio.h>
#include <unistd.h>
#include <asm/io.h>

#define BASEPORT 0x378 /* lp1 */

int main()
{
  /* Get access to the ports */
  if (ioperm(BASEPORT, 3, 1)) {perror("ioperm"); exit(1);}
  
  /* Set the data signals (D0-7) of the port to all low (0) */
  outb(0, BASEPORT);
  
  /* Sleep for a while (100 ms) */
  usleep(100000);
  
  /* Read from the status port (BASE+1) and display the result */
  printf("status: %d\n", inb(BASEPORT + 1));

  /* We don't need the ports anymore */
  if (ioperm(BASEPORT, 3, 0)) {perror("ioperm"); exit(1);}

  exit(0);
}

/* end of example.c */

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