// filename: Attiny85_spi
//Sketch uses 976 bytes (16%) of program storage space. Maximum is 6012 bytes.
//Global variables use 20 bytes of dynamic memory.
void setup() {
  // put your setup code here, to run once:
//Sample code for configuring ATtiny85 as slave and receive data:
#include<avr/io.h>
#include <I2Cdev.h>
#include <TinyWireM.h>
#include<TinyDebug.h>
String received_data;
//PB2 - SCL
//PB0 - SDA
short int fmax;
short int i=0;
initialize();
}
//====================================================== 
void loop() {
  // put your main code here, to run repeatedly main();
  main();
}
// =====================================================
void initialize()
{
  USICR=(1<<USIWM1)|(1<<USICS1)|(1<<USICLK);  //TWI mode
  DDRB=0x00; //SDA & SCL direction as input
  PORTB=0x00; //SDA & SCL default state
  USISR=0x00;       //Counter value
}
void i2c_address()
{
  char usi_data;
  while(USISIF==0);    //Wait till address bit is received
  {
    usi_data=USIDR;
    if(usi_data==0x00)  //Verifying the address
    {
      i2c_ack();   //Send acknowledge bit
   int   fmax=1;      
    }
  }
}

void i2c_ack()
{
  DDRB|=(1<<PB0);       //Set the direction to output
  USISR|=(1<<USIOIF);   //clear overflow flags
  PORTB|=(1<<PB0);
  while((USISR&0x01)==0); //Wait until counter goes 1
  PORTB&=~(1<<PB0);     //Ack bit end
  USISR&=0xF0;          //Clear counter bits
}

void receive_data()
{
  short int i=0;
  if(( fmax==1)&&(USIOIF==1))    //Checked address and counter overflow bits
  {
    received_data[i]=USIDR;   //Received data stored in string
    i++;
    USISR|=(1<<USIOIF);  //Clear overflow flag
  }
}

int main()
{
  initialize();      //i2c configuration
  i2c_address();     //check address
  i2c_ack();         //acknowledge bit
  while(1)
  {
   receive_data();   //receive data and storing data
  }
}