// heartbeat.c
// setup TCNT1 in PWM mode 
// setup TCNT3 in normal mode 
// set OC1A (PB5) as pwm output 
// pwm frequency:  (16,000,000)/(1 * (61440 + 1)) = 260hz
//

#include <avr/io.h>
#include <avr/interrupt.h>

uint16_t brightness[20] = { };

ISR(               ) {
  static uint8_t index=0;  //steps through the array 
                        ;  //set bounds on index
                        ;  //sset OCR1A to new value
}

int main() {
  // setup TCNT1 in PWM mode 
  //set PORTB bit 5 as the PWM output
  DDRB   = 0x20;          
  //fast PWM, set on match, clear at bottom, ICR1 holds value of TOP 
  TCCR1A |= 
  //use ICR1 as source for TOP, use clk/1
  TCCR1B |=
  //no forced compare 
  TCCR1C =
  //clear at 0xF000                               
  ICR1  =
  
// setup TCNT3 in normal mode to control the update rate 
// heartbeat update frequency = (16,000,000)/(8 * 2^16) = 30 cycles/sec
  //normal mode
  TCCR3A = 
  //use clk/8  (30hz)  
  TCCR3B =
  //no forced compare 
  TCCR3C =
  //enable timer 3 interrupt on TOV
  ETIMSK =

  sei();  //set GIE
  while(1) {}; //loop forever waiting for interrupt
 
}  // main