#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>

#define MASTER_ADDRESS (0b0100101)
#define SLAVE_ADDRESS (0b0100111)
#define LED_TOGGLE (0b00100010)

#define SLAVE

//Master

#ifdef MASTER

int current=0b00000010, previous=0b00000010, counter=0;

ISR(TWI_vect)
{
switch(TWSR)
{
case 0x08: //start
TWDR=SLAVE_ADDRESS<<1;
TWCR=0b11001101;
break;
case 0x18: //SLA+W transmitted, ACK recieved
TWDR=LED_TOGGLE;
counter+=1;
if(counter==2)
PORTB|=0b00000001;
else
PORTB&=0b11111110;
TWCR=0b10001111;
break;
case 0x20:
PORTB|=0b00000001;
break;
case 0x30:
PORTB|=0b00000001;
break;
case 0x38:
PORTB|=0b00000001;
break;
case 0x10:
PORTB|=0b00000001;
break;
case 0x28: //data transmitted, ACK recieved
TWCR=0b10011111;
break;
}
}

int main(void)
{
DDRB=0b00000001;
PORTB=0b00000010;
TWAR=MASTER_ADDRESS;
SREG|=0b10000000;
while (1)
{
if((PINB&0b00000010)==0b00000000)
_delay_ms(5);
current=PINB&0b00000010;
if((previous==0b00000010)&&(current==0b00000000))
{
TWCR=0b10100101;
}
previous=current;
}

}

#endif

#ifdef SLAVE

//Slave

int counterSlave=0;

ISR(TWI_vect)
{
switch(TWSR)
{
case 0x60:
TWCR=0b11000101;
break;
case 0x80:
if(TWDR==LED_TOGGLE)
counterSlave+=1;
TWCR=0b11000101;
break;
case 0xA0:
TWCR=0b01000101;
break;
}
}

int main(void)
{
DDRB=0b00000001;
PORTB=0b00000010;
SREG|=0b10000000;
TWAR=SLAVE_ADDRESS<<1;
TWCR=0b01000101;
while (1)
{
if ((counterSlave%2)==1)
PORTB|=0b00000001;
else
PORTB&=0b11111110;
}
}

#endif