//---------------------------------------------------------------
// EXAMPLE EX19.C :  Demonstrate use of an 80188 TIMER INTERRUPT.
//
// C.P. Diduch, Dec 1999.
//---------------------------------------------------------------
#define	KEY_PA	0x138	   // 82C55A port addresses for PA,
#define KEY_PB	0x13A	   // PB,
#define KEY_PC	0x13C	   // PC and the
#define KEY_CON	0x13E	   // Control Register.

#define	TRUE    1

#define	T1CNT   0xFF58     // 80C188 TIMER1 count register.
#define	T2CNT   0xFF60     // 80C188 TIMER2 count register.
#define	T1CON   0xFF5E     // 80C188 TIMER1 control register.
#define	T2CON   0xFF66     // 80C188 TIMER2 control register.
#define	T1CMPA  0xFF5A     // 80C188 TIMER1 max count register.
#define	T2CMPA  0xFF62     // 80C188 TIMER2 max count register.

#define	I_TYPE  18         // 80C188 Interrupt TYPE for TIMER1.
#define	TCUCON  0xFF32     // 80C188 Control reg addr for TIMERS.
#define	EOI     0xFF22     // 80C188 End of interrupt register.

#include <dos.h>           // Prototypes for enable(), disable().
#include <conio.h> 	   // conio.h contains prototypes for 
			   // inportb() and outportb(). 
void delay(unsigned MILLISECS);
void int_vect_init(void);
void timer_init(void);
void interrupt isr_0(void);
//---------------------------------------------------------------
unsigned N;                 // N is a global variable!

void main()
{
unsigned X;

outportb(KEY_CON, 0x82);   // Initialize 82C55A PPI with ports 
			   // KEY_PC and KEY_PA as OP ports and 
			   // port PB as an IP port.
N = 0;
disable();	           // Clear 80C188 interrupt flag'
int_vect_init();	         
timer_init();
enable();		   // 'Set 80C188 interrupt flag'
		
while (TRUE) { 
   delay(10000);
   }
}
//---------------------------------------------------------------
void int_vect_init(void) {
                                      
// Initialize interrupt vector table   
// entry for an interrupt type = I_YPE.
                                  
asm {
   push ax
   push bx
   push ds
   mov ax, 0
   mov ds, ax
   mov bx, I_TYPE*4
   mov word ptr[bx], offset isr_0
   mov word ptr[bx+2], seg isr_0
   pop ds
   pop bx
   pop ax
   }
}
//---------------------------------------------------------------
// Timer Interrupt Service Routine

void interrupt isr_0(void) {

   if (N < 10) {
      outportb(KEY_PC, 0x80^inportb(KEY_PC));
      N = N + 1;
      }
   else {
      outport(TCUCON, 0x0008);	// 'Mask off timer interrupts by
      }                         // setting bit-3 in TCUCON'
   outport(EOI, 0x0008);        // 'End of interrupt command'
}
//---------------------------------------------------------------
void timer_init(void) { 

// Initialize the 80C188XL TIMER-COUNTER UNIT and INTERRUPT
// CONTROLLER for a 1.0 second Periodic Interrupt.

   outport(T2CNT,0); 		// 'Clear TIMER2 count register'
   outport(T1CNT,0);		// 'Clear TIMER1 count register'
   outport(T2CMPA,40000);       // 'Set TIMER2 COUNT value for a
				// freq = 4 MHz / 40000 = 100 Hz'
   outport(T1CMPA,100);         // 'Set TIMER1 count value for a
				// freq = 100 Hz / 100 = 1.0 Hz'
   outport(T2CON,0xC001);	// 'TIMER2 control word for 
  				// continuous counting'
   outport(T1CON,0xE009); 	// 'TIMER1 control word to enable
				// interrupt generation and
				// pre-scaling by TIMER2'
   outport(TCUCON, 0);    	// 'Set up interrupt controller
                         	// and unmask internal timer
				// interrupts'
//---------------------------------------------------------------
void delay(unsigned MILLISECS) { // Implements a software delay.

unsigned M;

while (MILLISECS != 0) {
   M = 320;
   while (M != 0) {
      M--;
      }
   MILLISECS--;
   }
}