[AVR] ATMega88 and ATMega168 with USART interrupts

        unsigned int USART_BAUDRATE = 9600;		
	unsigned int ubrr = (((F_CPU / (USART_BAUDRATE * 16UL))) - 1);	
	
	UBRR0H = (unsigned char)(ubrr>>8);
	UBRR0L = (unsigned char)ubrr;
	
	UCSR0B = (1<<RXEN0)|(1<<TXEN0);
 
	UCSR0C = (1<<USBS0)|(3<<UCSZ00);

	UCSR0B |= (1<<RXCIE0);

ISR(USART_RX_vect)
{
	uint8_t W_buffer[8];
	
	int i;
	for (i=0;i<8;i++)
	{
		W_buffer[i]=usart_receive();	
		usart_transmit(W_buffer[i]);			
	}	
	
	usart_transmit('#');	
 }


void usart_transmit(uint8_t data)
{
	while ( !( UCSR0A & (1<<UDRE0)) );
	UDR0 = data;
}

uint8_t usart_receive( void )
{
	return UDR0; 
}

#define DATA_LIMIT 100 //for example, check your available RAM

volatile char rx_data[DATA_LIMIT]; //buffer
volatile unsigned int drc=0; //rx fill pointer
volatile unsigned int dsc=0; //rx read pointer

ISR(USART0_RX_vect){
	char data;
	//RXC0 got 1, recieved data
	data=UDR0;
	rx_data[drc++]=(data);
	if (drc>=(DATA_LIMIT))drc=0;
}

uint8_t usart_receive( void ){
	char data;
	while(drc==dsc); //wait for data if there isn't data in buffer
	data=rx_data[dsc++];
	if (dsc>=(DATA_LIMIT))dsc=0;
	return data; 
}
//you don't like to wait for data? ask first!
uint8_t usart_kbhit( void ){
	return (drc!=dsc); 
}

... and some where in your main program (after your init)...


	uint8_t W_buffer[8];
	
	int i;
	for (i=0;i<8;i++)
	{
		W_buffer[i]=usart_receive();	//should wait for characters?
		usart_transmit(W_buffer[i]);			
	}		
	usart_transmit('#'); //will be send after 8 receives???

int main(void){
 char d;
 init(); //init everything here
 while(1){
  d=usart_receive(); //to work with?
  usart_transmit(d);
 }
}