#include <Mega32.h>
#include <delay.h> 
#include <math.h> // for sine

//I like these definitions
#define begin {
#define end   } 
#define countMS 62  //ticks/mSec
 
unsigned long accumulator @0x2f0;
unsigned char highbyte @0x2f3; //the HIGH byte of the accumulator variable
unsigned long increment;			
char sineTable[256] @0x300;  //need loc to avoid glitch
unsigned int i, time ;
char amp, count;

interrupt [TIM0_OVF] void sgen(void)
begin 
	//the DDR code and scaling
	accumulator = accumulator + increment ;
	OCR0 = 128 + sineTable[highbyte] >> amp ;  
	
	//generate rising amplitude
	// 62 counts is about 1 mSec
	count--;
	if (0 == count )
	begin
		count=countMS;
		time++;    //in mSec
	end  
end 
 
void main(void)
begin 
   
   DDRB=0xff; 
   
   //fast PWM mode, full clock rate, toggle oc0 (pin B3) 
   //16 microsec per PWM cycle implies max freq for 16 samples of
   // 1/(16e-6*16) = 3900 Hz.
   //TCCR0 = 0b01101001 ; 
   //turn on timer 0 overflow ISR
   TIMSK = 0b00000001 ;
   
   //init the sine table
   for (i=0; i<256; i++)
   begin
   		sineTable[i] = (char)(127.0 * sin(6.283*((float)i)/256.0)) ;
   end  
   
   //init the DDS phase increment
   increment = 0x08ffffff ;
   time=0;
   TCCR0 = 0b00000001 ;  
   
   #asm
   sei
   #endasm
   
   while(1) 
   begin  
      
     if (time==50) 
     begin 
         time=0;
         //phase lock the sine gen and timer
         accumulator = 0;
         TCNT0 = 0; 
         OCR0 = 0;
         //generate the amplitude scaling -- start with divide by 16
         amp = 4;
         //turn on pwm  
         TCCR0 = 0b01101001 ;  
     end //if 
     
     if (time==1) amp=3; //ramp up
     if (time==2) amp=2;
     if (time==3) amp=1;
     if (time==4) amp=0;
       
     if (time==10) amp=1;  //ramp down
     if (time==11) amp=2;
     if (time==12) amp=3 ;
     if (time==13) amp=4;
     
     if (time==14) TCCR0=0b00000001 ;
    
   end // end while 
end  //end main