byte blinks[10] = {
  0b0001, 0b0000, 0b0010, 0b0000, 0b0000, 0b0000, 0b0000, 0b0000, 0b0100, 0b1000};
byte delays[10] = {
  0b0000, 0b0000, 0b0000, 0b0000, 0b0000, 0b0000, 0b0000, 0b0000, 0b0100, 0b1000};

unsigned int revolution;
unsigned int digittime;
unsigned int delayy;
unsigned int blinkdur;
byte digit;

void setup()
{
  Serial.begin(9600);

  shift();

  cli();

  TCCR1A = 0;
  TCCR1B = 0;
  TCCR1C = 0;
  TCNT1 = 0;



  TCCR1B = 0b11;  //64 divisor;
  TIMSK1 |= (1 << OCIE1A);

  sei();

  DDRD |= 0xF0;    //pins 4-7 as output;

  attachInterrupt(0, rev, RISING);  //Pin 2
}

void loop()
{
  if(Serial.available() >= 4)
  {
    for(byte x = 0; x < 10; x++)
    {
      blinks[x] = 0;
      delays[x] = 0;
    }
    byte digits[4];
    Serial.readBytes((char*)digits, 4);
    for(byte x = 0; x < 4; x++)
      digits[x] -= '0';

    for(byte r = 0; r < 4; r++)
    {
      if(digits[r] <= (6 + r))
      {
        byte pos = (6 + r) - digits[r];
        blinks[pos] |= _BV(3 - r);
      }
      else
      {
        byte pos = (16 + r) - digits[r];
        blinks[pos] |= _BV(3 - r);
        delays[pos] |= _BV(3 - r);
      }


    }

/*
    if(digits[0] <= 6)
    {
      byte pos = 6 - digits[0];
      blinks[pos] |= 0b1000;
    }
    else
    {
      byte pos = 16 - digits[0];
      blinks[pos] |= 0b1000;
      delays[pos] |= 0b1000;
    }

    if(digits[1] <= 7)
    {
      byte pos = 7 - digits[1];
      blinks[pos] |= 0b100;
    }
    else
    {
      byte pos = 17 - digits[1];
      blinks[pos] |= 0b100;
      delays[pos] |= 0b100;
    }
*/





    shift();
  }

}

void shift()
{
  for(byte x = 0; x < 10; x++)
    blinks[x] = blinks[x] << 4;
  for(byte x = 0; x < 10; x++)
    delays[x] = delays[x] << 4;
}

void rev()
{
  TCCR1B = 0;                    //stop timer
  revolution = TCNT1;            //note time for revolution
  TCNT1 = 1;                     //reset Timer
  digittime = revolution / 10 + (revolution / 700);   //calculate time per digit
  OCR1A = digittime;             //set compare match to next digit



  delayy = digittime * 2;        //microsecondsdelay until 2nd pass
  blinkdur = delayy / 10;        //calulate blink duration
  delayy = delayy - blinkdur;    //calculate delay between 2 digits
  digit = 1;                     //reset digit counter

  delayMicroseconds(delayy);

  byte x = blinks[0] & (~delays[0]);
  PORTD ^= x;
  delayMicroseconds(blinkdur);
  PORTD ^= x;

  TCCR1B = 0b11;                 //restart timer
}

ISR(TIMER1_COMPA_vect, ISR_NOBLOCK)
{
  byte x = blinks[digit] & (~delays[digit]);
  PORTD ^= x;
  delayMicroseconds(blinkdur);
  PORTD ^= x;


  delayMicroseconds(delayy);


  x = blinks[digit] & delays[digit];
  PORTD ^= x;
  delayMicroseconds(blinkdur);
  PORTD ^= x;

  TCCR1B = 0;
  OCR1A += digittime;
  TCCR1B = 0b11;
  digit++;
}