//---------------------------------------------------------------------------
// L351.C
// Program that uses the 80C188 Internal Timer for periodic interrupt
// interrupt generation. LED-5 is toggled 80-times with each interrupt.
//
// C/C++ code for the SBC188 boards.
// C.P. Diduch, March 1999.
//---------------------------------------------------------------------------
#define KEY_PA    0x0138        // Parallel port 'KEY BOARD' addresses.
#define KEY_PB    0x013A
#define KEY_PC    0x013C
#define KEY_CON   0x013E

#define EOI       0xFF22        // 80C188XL EOI (end of interrupt) port.
#define IT_TYPE   18            // 80C188XL Interrupt TYPE no. for TIMER1.
#define TCUCON    0xFF32        // 80C188XL Interrupt control port for TIMERS.

#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 maximum count register.
#define T2CMPA    0xFF62        // 80C188 TIMER2 maximum count register.

#define TRUE      1

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

void int_vect_init(void);       // Function prototypes.
void ppi_init(void);
void int_con_init(void);
void timer_80188_init(void);    
void delay(unsigned MILLISECS);     
void interrupt far timer_80188_int_handler(void);        

int N;

//---------------------------------------------------------------------------
void main(void)
{
disable();                      // Clear interrupt flag.
N = 0;				// Number of times interrupt handler has run.
ppi_init();                     // Initialize parallel ports.
int_vect_init();                // Initialize interrupt vector table.
enable();                       // Set interrupt flag.
timer_80188_init();
int_con_init();                 // Initialize interrupt controllers. 

while(TRUE) {                   // Main program simply waits
   delay(5000);                 // for interrupts to occur.
   }
}

//---------------------------------------------------------------------------
// Timer Interrupt Service Routine

void far interrupt timer_80188_int_handler(void)
{
if((N++) < 80) {
   outportb(KEY_PC, 0x20^inportb(KEY_PC));
   }
else {                       // Turn 80188 TIMER1 interrupt off  
   outport(TCUCON, 0x0009);      
   }
   outport(EOI, 0x0008);        // Specific End of Interrupt for TIMER1.
				// Reqired TYPE = 08D for all TIMERS.
}

//---------------------------------------------------------------------------
void int_vect_init(void)
{
asm {
   push ds
   push bx
   push ax

   mov ax, 0
   mov ds, ax
	
   mov bx, IT_TYPE*4
   mov word ptr [bx], offset timer_80188_int_handler  
   mov word ptr [bx+2], seg timer_80188_int_handler  

   pop ax
   pop bx
   pop ds
   }
}

//---------------------------------------------------------------------------
void timer_80188_init(void)
{
// Initialize the 80C188XL internal TIMER-COUNTER and INTERRUPT CONTROLLER
// for a 2.0 Hz. periodic interrupt. Refer to Chapter 8 and 9 in the 
// 80C188XL/80C186XL Microprocessor Unsers Manual.

outport(T1CON, 0x4009);         // Disable TIMER1.
outport(T2CON, 0x4009);         // Disable TIMER2.
outport(T1CNT, 0);              // Clear TIMER1 count register.
outport(T2CNT, 0);              // Clear TIMER2 count register.
outport(T2CMPA, 20000);         // Set TIMER2 COUNT value time-out 
				// periodically at 4 MHz/20000 = 200 Hz.
outport(T1CMPA, 50);            // TIMER1 is programmed to generate a
				// periodic interrupt at 200 Hz/100 = 4 Hz.
outport(T1CON, 0xE009);         // TIMER1 control word for enabling
				// interrupt generation and pre-scaling
				// by TIMER2.
outport(T2CON, 0xC001);         // TIMER2 control word for continuous counting.
}

//---------------------------------------------------------------------------
void ppi_init(void)
{                               // Inititialize 8255A KEYBOARD port
outportb(KEY_CON, 0x92);        // PA as output.
}

//---------------------------------------------------------------------------
void int_con_init(void)
{
outport(TCUCON, 0x01);          // Set up interrupt controller and
				// unmask internal timer interrupts with
				// priority 001.
}

//---------------------------------------------------------------------------
void delay(unsigned MILLISECS)
{
int M;
while (MILLISECS != 0) {
   M = 375;
   while (M != 0) {
	  M--;
	  }
   MILLISECS--;
   }
}