void setup() {

  OCR1B = 0x127;  // Output (PB4) goes to 0 at count 127, this gives 50% duty cycle.
  OCR1C = 0x255;  // timers resets at value 255, i.e., with freq PLL_freq/256.
                  // At PLL_freq = 64Mhz, this means 250Khz

  pinMode(PB4, OUTPUT);            // Enable PWM output pin


  // Enable 64 MHz PLL and use as source for Timer1
  PLLCSR = 1<<PCKE | 1<<PLLE;   

  // Waits until the bit PLOCK is set, which is once PLL has locked.
  // while ( (PLLCSR & (1<<PLOCK)) == 0){}    

  // Set up Timer/Counter1 for PWM output
  TIMSK = 0;                     // Timers interrupts are all OFF

  // Non needed if PMW1 is set.
  // TCCR1 |= 1<<CTC1;  // Reset the timer after a match with  OCR1C
  
  TCCR1 = 1<<CS10;               // 1:1 prescale
  GTCCR |= 1<<PWM1B; // PWM B,
  GTCCR |=  1<<COM1B1;  // OC1x cleared on compare match. Set when TCNT1 = $00.



}

void loop() { }