MIDI met AVR probleem

#include <stdio.h>
#include <stdbool.h>

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

#define PWMDDR     	DDRD
#define PWMPIN     	PD6
#define PWMENDDR	DDRD
#define PWMENPIN	PD2 //INT0
#define PWMENPORT	PORTD

#define NOTE 0x3C //Note C4

//set desired baud rate

#define BAUDRATE 31250

//calculate UBRR value

#define UBRRVAL ((F_CPU/(BAUDRATE*16UL))-1) //Divide by 8 i.s.o. 16 if U2X0 bit is set
//#define UBRRVAL ((F_CPU/(BAUDRATE*8UL))-1) //Divide by 16 i.s.o. 8 if U2X0 bit is not set

volatile uint8_t rxbuff; //Last character read from the UART
volatile uint8_t laststatus;
volatile uint8_t lastnote;
volatile uint8_t lastvelocity;
volatile uint8_t databyteindex;

const unsigned char VelocityToPWM[] PROGMEM =
{
	0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,
	46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78,80,82,84,86,88,
	90,92,94,96,98,100,102,104,106,108,110,112,114,116,118,120,122,124,
	126,128,130,132,134,136,138,140,142,144,146,148,150,152,154,156,158,
	160,162,164,166,168,170,172,174,176,178,180,182,184,186,188,190,192,
	194,196,198,200,202,204,206,208,210,212,214,216,218,220,222,224,226,
	228,230,232,234,236,238,240,242,244,246,248,250,252,254
};

void USART_Init(uint16_t ubrr)
{
	UBRR0H = (uint8_t)(ubrr>>8);
	UBRR0L = (uint8_t)(ubrr & 0xFF);
	//UCSR0A |= _BV(U2X0); //Improves baud rate error
	//Enable receiver and transmitter and Rx complete interrupt (must provide routine)
	UCSR0B |= _BV(RXEN0) | _BV(TXEN0) | _BV(RXCIE0);
	// Set frame format: asynchronous, no parity, 8 bit data, 1 stop bit
	UCSR0C = _BV(UCSZ01) | _BV(UCSZ00);
}

void note_off(void)
{
	if (lastnote == NOTE)
	{
		OCR0A = 0; //Set compare value to 0, so PWM is off
	}
}

void note_on(void)
{
	if (lastvelocity == 0) {note_off();}
	else {
		if (lastnote == NOTE)
		{
			OCR0A = pgm_read_byte(&(VelocityToPWM[lastvelocity]));		
		}
		//OCR0A = 0xBF; //Set PWM duty cycle to 3/4
	}
}

int main(void)
{
	uint8_t temp;

	DDRD &= ~_BV(PD3);
	PORTD = 0;

	DDRB |= _BV(PB1);
	PORTB = 0;

	//Set PWM pin as output
	PWMDDR |= _BV(PWMPIN);
	OCR0A = 0; //Set compare value to 0, so PWM is off
	//Set Timer0 as 8-bit FastPWM, set when upcounting and running at full MCU clock
	TCCR0A = ( (_BV(WGM01) | _BV(WGM00) | _BV(COM0A1)) & ~_BV(COM0A0) );
	TCCR0B = ( _BV(CS00) & ~_BV(WGM02) & ~_BV(CS01) & ~_BV(CS02) );	

	PWMENDDR &= ~_BV(PWMENPIN); //Set as input
	PWMENPORT |= _BV(PWMENPIN); //Enable pull-up resistor

	EICRA = (_BV(ISC01) & ~_BV(ISC00)) | (_BV(ISC10) & ~_BV(ISC11)); //Set INT0 for falling edge, INT1 for logical change
	EIMSK |= _BV(INT0) | _BV(INT1);

	USART_Init(UBRRVAL);

	sei();

	while(1)
	{
		temp = rxbuff;
		if (temp!=0) {
			rxbuff = 0;

			//Send the received data back

			//wait for empty transmit buffer
			while (!(UCSR0A&(1<<UDRE0))){};
			//send received data back
			UDR0=temp;


			//Process the received data

			if (bit_is_set(temp,7)) //Status byte 
			{
				if (temp < 0xF8)
				{
					laststatus = temp;
					databyteindex = 0;
				}
				else {} //System Realtime message, just ignore
			}
			else //Data byte
			{
				databyteindex++;
				switch (laststatus & 0xF0) //Command part of the status byte
				{
					case 0x90: //Note on
					{
						switch (databyteindex) {
							case 1: lastnote = temp; break;
							case 2: lastvelocity = temp; databyteindex = 0; note_on(); break;
							default: databyteindex = 0; break; //This should never happen!!
						}
						break;
					}
					case 0x80: //Note off
					{
						switch (databyteindex) {
							case 1: lastnote = temp; break;
							case 2: lastvelocity = temp; databyteindex = 0; note_off(); break;
							default: databyteindex = 0; break; //This should never happen!!
						}
						break;
					}
				}
			}
		}
	}

	return 0;

}

ISR (INT0_vect)
{
	OCR0A = 0; //Set compare value to 0, so PWM is off
	//OCR0A = 0xBF; //Set PWM duty cycle to 3/4
}

ISR (INT1_vect) //Only for debugging
{
	//copy input bitstream to output PB1
	if (bit_is_set(PIND,PD3)) {PORTB |= _BV(PB1);}
		else {PORTB &= ~_BV(PB1);}
}

/*
 * UART receive interrupt.  Fetch the character received and buffer
 * it, unless there was a framing error.
 */
ISR (USART_RX_vect)
{
 	uint8_t c;
 	
	c = UDR0;
 	if (bit_is_clear(UCSR0A, FE0)) //No framing error
   	{
		rxbuff = c;
    }
}