//RTI (Real Time Interrupt) programming with CodeWarrior on HCS12G128 Tower Module 
//PTT4 toggles continuously while waiting for an Interrupt from RTI
//PTT7 Toggle every Second using RTI (real time interrupt)
//By default RTI uses an internal 1 MHz oscillator as clock source 
//Make sure the jumers for LED1 and LED4 are set

 
//Modified from example 11-18C of HCS12 textbook by Mazidi & Causey.
//Thanks to Shu-Jen Chen for his contribution

//See Chapter 10 of HCS12G Ref. Manual for RTI register name and information. 
//The HCS12G series has different name for the RTI registers than the HCS12D covered in the Mazidi textbook 
 
//Make sure to choose "minimal startup code" and "Small" for memory model(no banked) when creating project for Interrupts  

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

void MSDelay(unsigned int);
unsigned int COUNT;
void main(void) 
{
  DDRT = 0b10010000;   //PT7 and PT4 = output
 
//Real Time Interrupt (RTI) setup. See chapter 10 section 10.3.2 for registers. 
//Notice Register names for RTI in HCS12G128 are different from what is in the Mazidi textbook 
//Notice from Table 10-11 the HCS12G128 also supports Decimal Freq Divide for RTI. 
//The decimal option for RTI divide did not exist in HCS12Dxx. Table 11-5 in Mazidi textbook is for HCs12D chips.
  CPMUINT = CPMUINT | CPMUINT_RTIE_MASK;     //enable RTI. See chapter 10.2 for HCS12G register names 	
  CPMURTI = 0x80 + 0x39;	// 1 MHz / (10 * 10 * 10^3) = 10 Hz (Change this number to see toggling rate for RTI)	
  COUNT = 0;				
   
 
    
   __asm CLI;  		//Enable interrupts globally
  //EnableInterrupts;  	//another way to Enable interrupts globally			
  
  for(;;)    			//  Toggle PTT4 forever and wait for interrupt
  {                            //do something
  PTT = PTT ^ 0b00010000;     //toggle PT4 continuously 
  MSDelay(100);
  
  } //stay here in this loop until an interrupt comes in.
}

//------ Real Time Interrupt ISR (Toggling the PORTT7 every one Sec.)
interrupt (((0x10000-Vrti)/2)-1) void RTI_ISR(void)
//interrupt VectorNumber_Vrti void RTI_ISR(void)  //another way to declare interrupt
{
  COUNT++;					
  if(COUNT == 10) 	//10 x 0.1 sec = 1 sec, also change this number for shorter or longer RTI toggling durations
  {
    PTT = PTT ^ 0x80; 	//Toggle PTT7
    COUNT = 0;      			
  }
  CPMUFLG = CPMUFLG | CPMUFLG_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<1000;j++);
}