parallel port programming under Unix

First you need to allow access to the port for your process.  First, you need to enable the port, then just use outb(port, char) to talk to it.

For example:

/* pioexample.c         Example of using PIO to talk to an I/O port
 *
 * Little ditty to count bits on the parallel port output register.
 */

#include <unistd.h>
#include <sys/types.h>
#include <sys/syscall.h>
#include <machine/sysarch.h>
#include <machine/pio.h>

/* ioport(port)         permit access to an I/O port.
 * port                 I/O address to enable
 */
void
ioport(int port) {
        u_long iomap[32];
        struct i386_set_ioperm_args ioperm;
 
        ioperm.iomap = iomap;
        syscall(SYS_sysarch, I386_GET_IOPERM, (char *) &ioperm);
        iomap[port >> 5] &= ~(1 << (port & 0x1f));
        syscall(SYS_sysarch, I386_SET_IOPERM, (char *) &ioperm);
}

int
main() {
        int i;
        ioport(0x378);                  /* Enable access to the port */
        for(i = 0; i < 256; i++) {
                outb(0x378, i);         /* Set the output register   */
                sleep(1);               /* Sleep a tick              */
        }
        return 0;
}