LED PWM funktionniert nicht!

#include <avr/io.h>

#include <avr/interrupt.h>

#include <util/delay.h>

#define F_CPU 8000000UL // 8 MHz

#define LED_PORT  PORTB

#define LED_DDR    DDRB

#define LED_PIN    PINB

#define PWM_LED    PB2

ISR(TIMER1_COMPA_vect){

  LED_PORT |= (1<<PWM_LED);

}

ISR(TIMER1_COMPB_vect){

  LED_PORT &= ~(1<<PWM_LED);

}

int main(void)

{

  //Timer1 Config

  //Clear OCnA/OCnB on compare match

  //Fast PWM: Top = OCR1A (siehe Table 17-2, uC Atmega2560, Seite 148)

  TCCR1A |= (1<<COM1A1)|(1<<COM1B1)|(1<<WGM11)|(WGM10);

  //No prescaling

  TCCR1B |= (1<<WGM13)|(1<<WGM12)|(1<<CS12);

  TCNT1 = 0;

  OCR1A = 0xFFFF;

  OCR1B = 0x7FFF;

  TIMSK1 |= (1<<OCIE1B)|(1<<OCIE1A);

  LED_DDR |= (1<<PWM_LED);  //Alle Ausgänge

  LED_PORT = 0xff;

  sei();

    while(1)

    {

    }

}