/* Program to write a character to the parallel port */

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

#define ON  1
#define OFF 0

// address of LPT1
#define lptBase 0x378

// address offsets from the base-address, on the lp port
#define dataAdd lptBase
#define statAdd lptBase + 1
#define cntlAdd lptBase + 2

void main(int argc, char *argv[])
{
    char c;

    if (argc == 2) {
        c = argv[1][0];
    }
    else {
        c = 'A';
    }

    // Get access to parallel port registers
    if (ioperm(lptBase,3,ON) == -1) {
        fprintf(stderr,"Cannot get permission to access parallel port.\n");
        fprintf(stderr,"You need to be superuser to do this.\n");
        perror("ioperm");
        exit(1);
    }

    printf("Writing a \'%c\' to the parallel port\n",c);
    outb(c,dataAdd);
    printf("Parallel port returns a \'%c\'\n",inb(dataAdd));

    // No longer need to use parallel port
    ioperm(lptBase,3,OFF);
}