#define F_CPU 1000000UL  // 1 MHz
#define BAUD 2400

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/signal.h>
#include <avr/delay.h>
#include <stdio.h>
#include <stdarg.h>

#define RX_BUFFER_SIZE 128

#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

void beginSerial(long);
void serialWrite(unsigned char);
int serialAvailable();
int serialRead();
void serialFlush();


unsigned char rx_buffer[RX_BUFFER_SIZE];

int rx_buffer_head = 0;
int rx_buffer_tail = 0;
void beginSerial(long baud)
{
#if defined(__AVR_ATmega168__)
	UBRR0H = ((F_CPU / 16 + baud / 2) / baud - 1) >> 8;
	UBRR0L = ((F_CPU / 16 + baud / 2) / baud - 1);
	
	// enable rx and tx
	sbi(UCSR0B, RXEN0);
	sbi(UCSR0B, TXEN0);
	
	// enable interrupt on complete reception of a byte
	sbi(UCSR0B, RXCIE0);
#else
	UBRRH = ((F_CPU / 16 + baud / 2) / baud - 1) >> 8;
	UBRRL = ((F_CPU / 16 + baud / 2) / baud - 1);
	

	//  UCSRB = (1<<RXEN) | (1<<TXEN);

	// enable rx and tx
		sbi(UCSRB, RXEN);
	sbi(UCSRB, TXEN);
	
	// enable interrupt on complete reception of a byte
	sbi(UCSRB, RXCIE);
#endif
	
	// defaults to 8-bit, no parity, 1 stop bit
}

void serialWrite(unsigned char c)
{
#if defined(__AVR_ATmega168__)
	while (!(UCSR0A & (1 << UDRE0)))
		;

	UDR0 = c;
#else
	while (!(UCSRA & (1 << UDRE)))
		;

	UDR = c;
#endif
}

int serialAvailable()
{
	return (rx_buffer_head - rx_buffer_tail) % RX_BUFFER_SIZE;
}

int serialRead()
{
	// if the head isn't ahead of the tail, we don't have any characters
	if (rx_buffer_head == rx_buffer_tail) {
		return -1;
	} else {
		unsigned char c = rx_buffer[rx_buffer_tail];
		rx_buffer_tail = (rx_buffer_tail + 1) % RX_BUFFER_SIZE;
		return c;
	}
}

void serialFlush()
{
	// don't reverse this or there may be problems if the RX interrupt
	// occurs after reading the value of rx_buffer_head but before writing
	// the value to rx_buffer_tail; the previous value of rx_buffer_head
	// may be written to rx_buffer_tail, making it appear as if the buffer
	// were full, not empty.
	rx_buffer_head = rx_buffer_tail;
}

#if defined(__AVR_ATmega168__)
SIGNAL(SIG_USART_RECV)
#else
SIGNAL(SIG_UART_RECV)
#endif
{
#if defined(__AVR_ATmega168__)
	unsigned char c = UDR0;
#else
	unsigned char c = UDR;
#endif

	int i = (rx_buffer_head + 1) % RX_BUFFER_SIZE;

	// if we should be storing the received character into the location
	// just before the tail (meaning that the head would advance to the
	// current location of the tail), we're about to overflow the buffer
	// and so we don't write the character or advance the head.
	if (i != rx_buffer_tail) {
		rx_buffer[rx_buffer_head] = c;
		rx_buffer_head = i;
	}
}

void printMode(int mode)
{
	// do nothing, we only support serial printing, not lcd.
}

void printByte(unsigned char c)
{
	serialWrite(c);
}

void printNewline()
{
	printByte('\n');
}

void printString(char *s)
{
	while (*s)
		printByte(*s++);
}


int
main(void)
{
  char chh; int serIn;
 
sei();

  beginSerial(BAUD);
  while(1){

    if(serialAvailable()) {    
      while (serialAvailable()){
        serIn = serialRead();        
        serialWrite(serIn); 
      }
    }

 }

 

  return 0;
}