/*
 Generating a tone using DDS
*/
#include "TinyDebug.h"

unsigned int Acc;
unsigned int Note = 857; // Middle C

void setup() {
  // Enable 64 MHz PLL and use as source for Timer1
  PLLCSR = 1<<PCKE | 1<<PLLE;     

  // Set up Timer/Counter1 for PWM output
  TIMSK = 0;                     // Timer interrupts OFF
  TCCR1 = 1<<CS10;               // 1:1 prescale
  GTCCR = 1<<PWM1B | 2<<COM1B0;  // PWM B, clear on match

  pinMode(4, OUTPUT);            // Enable PWM output pin

  // Set up Timer/Counter0 for 20kHz interrupt to output samples.
  TCCR0A = 3<<WGM00;             // Fast PWM
  TCCR0B = 1<<WGM02 | 2<<CS00;   // 1/8 prescale
  TIMSK = 1<<OCIE0A;             // Enable compare match, disable overflow
  OCR0A = 49;                    // Divide by 400
}

void loop() { }

ISR(TIMER0_COMPA_vect) {
  Acc = Acc + Note;
  OCR1B = (Acc >> 8) & 0x80;
}