//Interrupt Programming with CodeWarrior on Project Board with HCS12 module 
//Buzzer sounds continuously while waiting for AN Interrupt from Real Time Interrupt (RTI) 
//PORTA.4 Toggle every Second using RTI (real time interrupt) 
//Modified by M. Mazidi from Example 11-18C of HCS12 textbook by Mazidi & Causey.

//Remember RTI uses the XTAL freq. (not the bus Freq) which is XTAL=4 MHz on HCS12 MCU Module 
 
//Make sure to choose "minimal startup code" and "Small" for memory model(no banked) when creating porject for Interrupts 
//In CodeWarrior,Make sure you are in TBDML Mode before downloading 
//Press F7 (to Make), then F5(Debug) to downLOAD,and F5 once more to start the program execution
   

#include <hidef.h>      /* common defines and macros */
#include "derivative.h"      /* derivative-specific definitions */

void MSDelay(unsigned int);
unsigned int COUNT;
void main(void) 
{
  
    DDRA = 0xFF;    //PORTA as output since LEDs are connected to it
    DDRP = DDRP | 0b00010000;  //on Project Board, the lower 4 bits of PA3-PA0 are connected to LEDs(LED1-LED4) permanently
    PTP = PTP & 0b11101111;    //and must be enabled by clearing bit P4 of PORTP
                //on Project Board,we need to connect 4 wires from LED5-LED8 (J10) to pins PA4-PA7 via J6 connector (pins 25,27,29,31)
      
    DDRT = 0b00000001;   //PT0 = output for Buzzer
  
  
 
 //Real time Interrupt (RTI) setup 
  CRGINT = CRGINT | CRGINT_RTIE_MASK;     //enable RTI 	
  RTICTL = 0b01111111;	//(longest RTI is about 0.13 sec) Change this number to see toggling rate for RTI	
  COUNT = 0;				
   
 
    __asm CLI;  	//Enable interrupts globally			
  
  for(;;)    //  Sound the Buzzer at PTT0 forever and wait for interrupt
  {                            //do something
  PTT = PTT ^ 0b00000001;     //sound the buzzer continuously 
  MSDelay(100);              //chnage this delay to hear different sound
  
  } //stay here in this loop until an interrupt comes in.
}

//------ Real Time Interrupt ISR (Toggling the PORTA4 every Sec.)
interrupt (((0x10000-Vrti)/2)-1) void RTI_ISR(void)
{
  COUNT++;					
  if(COUNT==2) 	//4 x 0.26 sec = 1 sec	also change this number for shorter or longer durations
  {
    PORTA = PORTA ^ PORTA_BIT4_MASK; 	//Toggle PORTA.4
    COUNT = 0;      			
  }
  CRGFLG = CRGFLG | CRGFLG_RTIF_MASK; //clear it for next round	
}
//-------end of ISR   
  
 void MSDelay(unsigned int itime)
  {
    unsigned int i; unsigned int j;
    for(i=0;i<itime;i++)
      for(j=0;j<311;j++);
  }