#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/signal.h>

unsigned char status = 0;
volatile unsigned char count;
volatile unsigned int count2;


void timer1 (void);
void master_init (void);
void master_transmit (unsigned char data);

SIGNAL (SIG_SPI) {
	return;
}

SIGNAL (SIG_OVERFLOW1) {				//Senderoutine
	if (count == 1) {
		master_transmit ('a');
		count--;
		return;
	}
	if (count == 0) {
		master_transmit ('b');
		count++;
	}
	PORTD ^= (1 << PD1);
}

void timer1 (void) {
	TIMSK1 |= _BV(TOIE1);           		//Timer Overflow Interrupt enable
	TCNT1 = 0;                				//Rücksetzen des Timers
	TCCR1B = _BV(CS10) | _BV(CS11);			//8MHz/65536/64 = 1,91Hz --> 0,5s
}

void master_init (void) {
	DDRB = _BV(PB2) | _BV(PB3) | _BV(PB5);		// setze SCK,MOSI,SS als Ausgang
	DDRB &= ~_BV(PB4);				// setze MISO als Eingang
	PORTB = _BV(PB5) | _BV(PB0);			// SCK und SS high (ist mit SS am Slave verbunden)
	SPCR = _BV(SPE) | _BV(MSTR) | _BV(SPR0);	//Aktivierung des SPI, Master, Taktrate fck/16
	status = SPSR;	
	DDRD |= (1 << PD1);				//Status löschen
}

void master_transmit (unsigned char data) {
	//PORTB |= _BV(PB0);
	PORTB &= ~_BV(PB2);				//SS am Slave Low --> Beginn der Übertragung
	SPDR = data;					//Schreiben der Daten
	while (!(SPSR & (1<<SPIF)));
	PORTB |= _BV(PB2);				//SS High --> Ende der Übertragung
}


int main (void) {

	master_init ();
	timer1 ();
	sei ();

	for (;;)
	{

	**************************************************************
	/*count2++;

	if(count2 == 5000)
	{
	count2 = 0;
	if (count == 1) {
		master_transmit ('a');
		count--;
		return;
	}
	if (count == 0) {
		master_transmit ('b');
		count++;
	}
	}*/
	***************************************************************
	}
}