/* 
 * EE 361L
 * Interrupt, Sleep and Watch Dog Timer example
 * 
 * It has a single interrupt INT, and keeps track
 * of the number of interrupts (so far) in a global
 * variable "count".  It continously outputs pulses
 * that have duration that is proportional to the 
 * value of count.  Thus, these pulses get longer
 * each each interrupt.
 *
 */

#include <htc.h>

#define LEDport  RB1 // RB1 is connected to the LED

unsigned char count;  // Global variable count (a byte)

main(){

unsigned char i;

TRISB = 1;     // All PORTB are output ports, except RB0/INT
               //  RB0/INT should be an input for the interrupt
               //  signal.
LEDport = 1;   // Initialize the LED to off
count = 1;     // Initialize count;

PSA = 1;       // Post scalar used with Watch Dog Timer
PS2 = 0;       // Rate is 1:2.
PS1 = 0;       // Time out is approx 2 x 18 ms = 36 ms
PS0 = 1;

INTEDG = 1;    // Interrupts are pos edge triggered
INTCON = 0;    // Disable all interrupts but..
INTE = 1;      // Enable the INT interrupt
INTF = 0;
GIE = 1;       // Allow interrupt signals

while(1) {
   for (i=0; i<count; i++) { // Breakpoint 1
      LEDport = 1;	// Breakpoint 2
   }   
   for (i=0; i<count; i++) {  // Breakpoint 3
      LEDport = 0;  // Breakpoint 4
   }
   SLEEP(); // SLEEP also clears the WDT
}	
}

/*
 * The following is the interrupt service routine (or
 * interrupt handler.  Apparently, it does not allow
 * breakpoints.  Actually, you can set a breakpoint but
 * the processor never recognizes it during simulation.  
 * A possible reason is that breakpoints are often
 * implemented using "software interrupts" (we'll
 * discuss these in lecture later in the semester). 
 * While in the interrupt handler, the processor
 * disables all interrupts, possibly disabling all
 * software interrupts too such as breakpoints.
 */

void interrupt servroutine()
{
count++; // Increment count
if (count == 0) count++; // In case of wrap-around to 0.
INTF = 0; // Clearing flag and reenabling the interrupt.

          // Recall that the GIE bit is automatically
          // set back to 1 when
          // the processor returns from this routine,
          // which also reenables interrupt signals.
}