/*
   FILE: toggle.c
   AUTH: P.OH
   DESC: ISR on IRQ3 for counting toggle switches
*/

#include<stdio.h>
#include<stdlib.h>
#include<dos.h>
#include<conio.h>

void interrupt (*oldIrq3)(void);
void interrupt countToggle(void);

/* GLOBALS */
int  i = 0;
long j = 0;

#define IRQ3  0x0b   /* IRQ3 */

int main(void)
{
  window(5,5,50,75);
  clrscr();
  gotoxy(1,3);
  cprintf("Do-while loop iteration # ");

  oldIrq3 = getvect(IRQ3);    /* save the old interrupt vector */
  setvect(IRQ3, countToggle); /* install the new interrupt handler */

  /* Unmask (i.e. enable) IRQ3.  This requires turning bit 3 to 0 */
  /* and bits 0,1,2,4,5,6,7 to 1.  Hence 11110111 binary = F7 hex */

  outportb(0x21, ( inportb(0x21) & 0xF7 ) ); /* Unmask (Enable) IRQ3 */

  do {
    j++;
    gotoxy(27,3); cprintf("%ld\n", j);
  } while(!kbhit());

  /* Key hit, so exit main.  But first, be nice and return things back */
  /* to original state */

  setvect(IRQ3, oldIrq3);
  outportb(0x21, (inportb(0x21) | 0x08) ); /* disable IRQ3 */

  printf("\nswitch presses i = %d\n", i);
  printf("j = %ld\n", j);

  return 0;

} /* end of main */

/* this ISR should execute each time IRQ3 goes high */
void interrupt countToggle(void)
{
  disable();
  i++;
  outportb(0x20, 0x20); /* send EOI signal */
  enable();
}