/* 2 x 8 dimming LEDs with Arduino Nano DCC decoder
   By German Trinidad and Norber, Spain, December 2015
   Freely distributable for private, non commercial, use

   Attach led anodes (+) to #1 to #8 outputs
   Attach all led catodes (-) to GNDs
   Don't forget to add serial resistors! */

#define ADR_MMAUS_01  129  // Assign here your addresses
#define ADR_MMAUS_02  130
#define ADR_MMAUS_03  131
#define ADR_MMAUS_04  132
#define ADR_MMAUS_05  133
#define ADR_MMAUS_06  134
#define ADR_MMAUS_07  135
#define ADR_MMAUS_08  136
#define ADR_MMAUS_09  137

byte comb[][4] = {
  //Address                      , Port                    , Pin-√ , Pin--
  {((ADR_MMAUS_01 - 1) / 4) + 128, ((ADR_MMAUS_01 - 1) % 4), 4     , 5   },
  {((ADR_MMAUS_02 - 1) / 4) + 128, ((ADR_MMAUS_02 - 1) % 4), 6     , 7   },
  {((ADR_MMAUS_03 - 1) / 4) + 128, ((ADR_MMAUS_03 - 1) % 4), 8     , 9   },
  {((ADR_MMAUS_04 - 1) / 4) + 128, ((ADR_MMAUS_04 - 1) % 4), 10    , 11  },
  {((ADR_MMAUS_05 - 1) / 4) + 128, ((ADR_MMAUS_05 - 1) % 4), 12    , 13  },
  {((ADR_MMAUS_06 - 1) / 4) + 128, ((ADR_MMAUS_06 - 1) % 4), 14    , 15  },
  {((ADR_MMAUS_07 - 1) / 4) + 128, ((ADR_MMAUS_07 - 1) % 4), 16    , 17  },
  {((ADR_MMAUS_08 - 1) / 4) + 128, ((ADR_MMAUS_08 - 1) % 4), 18    , 19  },
  {((ADR_MMAUS_09 - 1) / 4) + 128, ((ADR_MMAUS_09 - 1) % 4), 20    , 21  },
};

#define DCC_INT   2
#define SI        0
#define NO        1
#define TICKS    215           // Prescaler 8 -> Timer pulse every 0.5 µs -> 200 ticks are 100 µs
#define FREQ     120           // 15 ms aprox 
#define DELTA     3            // PWM
#define TO_OFF   20
#define PAUSE    30
#define TO_ON    40

volatile byte buf_dcc[6];
volatile byte pinPWM_1, pinPWM_2;
volatile boolean varyingLed = false;
volatile int duty = FREQ - 1;
volatile byte state = TO_OFF;

void setup() {
  for (int i = 4; i < 20; i++) {
    pinMode(i, OUTPUT);
    if (i & 0x01) digitalWrite(i, LOW);      // Green leds at odd pins start off
    else digitalWrite(i, HIGH);              // Red leds at even pins start on
  }
  pinMode(DCC_INT, INPUT);
  Serial.begin(9600);
  Serial.print("Iniciando...");
  delay(500);
  attachInterrupt(0, dcc_int, CHANGE);       // pin2 = DCC      externalInterrupt 0
  cli();
  TCCR0A = 0;
  TCCR0B = 0;
  TCCR0B |= (1 << CS01);                     // Set CS01 bit for 8 prescaler (0.5 µs) on Timer0 - DCC
  TCCR2A = 0;
  TCCR2B = 0;
  TCCR2B |= (1 << CS21);                     // Set CS21 bit for 8 prescaler (0.5 µs) on Timer2 - Dimming
  TIMSK2 = 0;
  TIMSK2 |= (1 << TOIE2);                    // Enable Timer2 Overflow interrupt
  sei();
}

void dcc_int() {                               // ISR(INT0_vect) External interrupt routine for signal on pin2
  static int tmp_pulse;                        // German is a genius!
  static byte bit_dcc;
  static byte preamb;
  static byte aux_dcc, x_or, idx, num_bits;

  if (PIND & (0x04)) TCNT0 = 0;
  else  {
    tmp_pulse = TCNT0;
    if (tmp_pulse > TICKS) bit_dcc = 0;
    else bit_dcc = 1;
    if (preamb == SI) {
      if (bit_dcc) {
        if (num_bits) num_bits--;
      }
      else {
        if (!num_bits) {
          preamb = NO;
          num_bits = 9;
          x_or = 0;
          idx = 0;
        }
        else num_bits = 10;
      }
    }
    else {
      if (--num_bits) aux_dcc = aux_dcc * 2 + bit_dcc;
      else {
        if (!bit_dcc) {
          buf_dcc [idx++] = aux_dcc;
          x_or ^= aux_dcc;
          num_bits = 9;
        }
        else {
          preamb = SI;
          num_bits = 10;
          if (x_or == aux_dcc) {                        // Data received OK!
           Serial.print(buf_dcc[0]);
            // buf_dcc[0] is Address
            // buf_dcc[1] is Port and command
            if (!varyingLed) {                          // While commuting, ignore commands
              byte port = (buf_dcc[1] & 0x06) >> 1;     // 0x06 = B0000 0110
              for (int i = 0; i < 9; i++) {
                if ((buf_dcc[0] == comb[i][0]) && (port == comb[i][1])) { // It's ours
                  if (buf_dcc[1] & 0x01) {
                    pinPWM_1 = comb[i][2];              // Pin to dim off
                    pinPWM_2 = comb[i][3];              // Pin to dim on
                  }
                  else {
                    pinPWM_1 = comb[i][3];
                    pinPWM_2 = comb[i][2];
                  }
                  if (digitalRead(pinPWM_1)) {          // Needs to be dimmed off indeed
                    varyingLed = true;
                    duty = 255;
                    state = TO_OFF;
                  }
                  return;
                }
              }
            }
          }
        }
      }
    }
  }
}

ISR(TIMER2_OVF_vect) {                         // Timer2 Overflow interrupt every 128 µs for dimmming leds
  if (varyingLed == true) {
    static int cont;
    cont++;
    switch (state) {
      case TO_OFF:
        if (cont == FREQ) {                    // High pulse starts when 'cont' reaches FREQ
          digitalWrite(pinPWM_1, HIGH);
          cont = 0;
          duty = duty - DELTA;
        }
        if (cont == duty) {
          digitalWrite(pinPWM_1, LOW);         // And ends when 'cont' reaches 'duty'
          if (duty < DELTA) state = PAUSE;
        }
        break;
      case PAUSE:
        if (cont == 5 * FREQ) {                 // Small dramatic pausae
          state = TO_ON;
          duty = DELTA;
          cont = 0;
        }
        break;
      case TO_ON:
        if (cont == FREQ) {
          digitalWrite(pinPWM_2, HIGH);
          cont = 0;
          duty = duty + DELTA;
          if (duty > 255 - DELTA) varyingLed = false;  // We're done
        }
        if (cont == duty) {
          digitalWrite(pinPWM_2, LOW);
        }
        break;
    }
  }
}

void loop() {
}