#include <Wire.h>

//#define DEBUG

static volatile byte rbuff[256];
static volatile uint8_t po;

void setup()
{
  Wire.begin(8);// Slave ID #8
  Wire.onRequest(requestEvent);
  Wire.onReceive(receiveEvent);

#ifdef DEBUG
  Serial.begin(19200);
#endif
}

void loop()
{
}

void receiveEvent(int num)
{
  byte rd;

  po = 0;
  while(Wire.available())
  {
    rd = Wire.read();
#ifdef DEBUG
    Serial.print((char)rd);
#endif
    rbuff[po] = rd;
    if(++po > 254)
      po = 0;
  }
  #ifdef DEBUG
    Serial.println();
#endif
}

void requestEvent()
{
  for(int i=0; i<po; i++)
  {
    Wire.write(rbuff[i]);
  }
}