Parallel Port - Computer Busses - page 271

#define EOI 0x20 /* End of Interrupt */
#define ICR 0x20 /* Interrupt Control Register */
#define IMR 0x21 /* Interrupt Mask Register */

void interrupt far pl_interrupt(void);
void setup_parallel (void);
void set_vectors(void);
void enable_interrupts(void);
void disable_interrupts(void);
void reset_vectors(void);
void interrupt far (*oldvect)();
int int_flag = TRUE;
int outval=0;
int main(void)
{
set_vectors();
setup_parallel();
do
{
if (int_flag)
{
printf("New value sent\n");
int_flag=FALSE;
}

} while (!kbhit());

reset_vectors();

return(0);

}
void setup_parallel(void)
{

outportb(CONTROL, inportb(CONTROL) | 0x10);

/* Set Bit 4 on control port to a 1 */

}

void interrupt far pl_interrupt(void)
{

disable();

outportb(DATA,outval);

if (outval!=255) outval++; else outval=0;

int_flag=TRUE;

outportb(ICR,EOI);

enable();

}
void set_vectors(void)
{
int int_mask;

disable(); /* disable all ints */

oldvect=getvect(0x0f); /* save any old vector */

setvect (0x0f,pl_interrupt); /* set up for new int serv */

}

void enable_interrupts(void)
{
int ch;

disable();

ch=inportb(IMR);

outportb(IMR, ch & IRQ7);

enable();