const unsigned long ROTARY_DEBOUNCE_TIME = 100; // milliseconds
const byte Encoder_A_Pin = 8;  // PB0, pin 12 (TQFP) on board
const byte Encoder_B_Pin = 9;  // PB1, pin 13 (TQFP) on board

// handle pin change interrupt for D8 to D13 here
ISR (PCINT0_vect)
{
static byte pinA, pinB;
static boolean ready;
static unsigned long lastFiredTime;

byte newPinA = digitalRead (Encoder_A_Pin);
byte newPinB = digitalRead (Encoder_B_Pin);

if (pinA == newPinA &&
pinB == newPinB)
return;    // spurious interrupt

// so we only record a turn on both the same (HH or LL)

// Forward is: LH/HH or HL/LL
// Reverse is: HL/HH or LH/LL

if (newPinA == newPinB)
{
if (ready)
{

  if (millis () - lastFiredTime >= ROTARY_DEBOUNCE_TIME)
  {
    if (newPinA == HIGH)  // must be HH now
    {
      if (pinA == LOW)
        fileNumber ++;
      else
        fileNumber --;
    }
    else
    { // must be LL now
      if (pinA == LOW)
        fileNumber --;
      else
        fileNumber ++;
    }
    if (fileNumber > MAX_FILE_NUMBER)
      fileNumber = 0;
    else if (fileNumber < 0)
      fileNumber = MAX_FILE_NUMBER;
    lastFiredTime = millis ();
    fired = true;
  }

  ready = false;
 }  // end of being ready
}  // end of completed click
else
ready = true;

pinA = newPinA;
pinB = newPinB;

}  // end of PCINT2_vect