programming

programming the parallel port interface in C is very easy.
the example programs work fine for me on a x86 architecture machine with linux. other architectures and operating systems are untested, but may work, too.

the following example shows how to set and read bits from the interface. actually a byte is read and written and - of course - must be encoded/decoded with a binary encoding to obtain the bits.

--- io-example.c ---

/*
 * Compile with `gcc -O2 [...]'.
 */

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

#define BASEPORT 0x278 /* lp2 */
/*#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 (1000 ms) */
  usleep(1000000);
  
  /* 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 io-example.c */

the following command line tool was designed for interactive and non-interactive operation. e.g. a bash script could use

echo "246x" |faco

to toggle the outputs 2, 4 and 6.

--- faco.c ---

/*
 * Compile with `gcc -O2 [...]'.
 * faco - Face Control Program
 * (c) 1998, Ben Fuhrmannek <ben@fuhrmannek.de>
 * released under GPL (GNU General Public License)
 */

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

#define BASEPORT 0x278 /* lp2 */
/*#define BASEPORT 0x378 /* lp1 */

int li[7];
int in[4];

ok(char x) {printf("%c: OK!\n",x);}
led(int l) /* l = 1..8 */
{
  int i, setz = 0;
  if (li[l-1] == 0) li[l-1] = 1; else li[l-1] = 0;
  setz = (1*li[0]) + (2*li[1]) + (4*li[2]) + (8*li[3]) +
              (16*li[4])+(32*li[5])+(64*li[6])+(128*li[7]);
  outb(setz,BASEPORT);
}

getIN()
{
  int i, wert;
  for (i=0; i <= 4; ++i) in[i] = 0;
  wert=inb(BASEPORT+1)-7;
  if (wert >= 128) {wert = wert - 128; in[0] = 1;}
  wert = 127 - wert;
  if (wert > 64) {wert = wert - 64; in[1] = 1;}
  if (wert > 32) {wert = wert - 32; in[2] = 1;}
  if (wert > 16) {wert = wert - 16; in[3] = 1;}
  if (wert > 8) in[4] = 1;
}

main()
{
  int i, j, ex = 1;
  char c;
  for (i = 0; i <= 7; ++i) li[i] = 0;
  if (ioperm(BASEPORT,3,1)) {perror("ioperm");exit(1);}
  outb(0,BASEPORT);
  while (ex > 0)
  {
    /* printf("--> "); */
    c = getchar();
    switch(c)
    {
    case '0':
      for (i = 0; i <= 7; ++i) li[i] = 0;
      outb(0,BASEPORT);
      break;
    case '1': led(1); break;
    case '2': led(2); break;
    case '3': led(3); break;
    case '4': led(4); break;
    case '5': led(5); break;
    case '6': led(6); break;
    case '7': led(7); break;
    case '8': led(8); break;
    case '9':
      for (i = 0; i <= 7; ++i) li[i] = 1;
      outb(255,BASEPORT);
      break;
    case 's':
      printf("LED");
      for (i = 0; i <= 7; ++i) printf(" : %d",li[i]);
      printf("\n");
      printf("status: %d OK!\n",inb(BASEPORT+1));
      getIN();
      printf("IN");
      for (i = 0; i <= 4; ++i) printf(" : %d",in[i]);
      printf("\n");
      break;
    case 'd':
      usleep(1000000);
      break;
    case 'x': ex = 0; break;
    default: /* printf("Falsche Eingabe!"); */ break;
    }
/*    ok(c); */
  }
  if (ioperm(BASEPORT,3,0)) {perror("ioperm");exit(1);}
}