text: /*
  // Emulate a DCF77 radio receiver to control an external clock
  //
  // a nice & free logic test program for DCF77 can be found here:
  https://www-user.tu-chemnitz.de/~heha/viewzip.cgi/hs/Funkuhr.zip/
  //
  // a DCF77 digital scope for Arduino boards can be found here:
  https://github.com/udoklein/dcf77
  //
  */
  
  #ifdef HAS_DCF77
  
  #include "dcf77.h"
  
  // Local logging tag
  static const char TAG[] = __FILE__;
  
  // triggered by second timepulse to ticker out DCF signal
  void DCF77_Pulse(time_t t, uint8_t const *DCFpulse) {
  
    TickType_t startTime = xTaskGetTickCount();
    uint8_t sec = second(t);
  
    t = myTZ.toLocal(now());
    ESP_LOGD(TAG, "[%02d:%02d:%02d.%03d] DCF second %d", hour(t), minute(t),
             second(t), millisecond(), sec);
  
    // induce 10 pulses
    for (uint8_t pulse = 0; pulse <= 9; pulse++) {
  
      switch (pulse) {
  
      case 0: // start of second -> start of timeframe for logic signal
        if (DCFpulse[sec] != dcf_Z)
          digitalWrite(HAS_DCF77, dcf_low);
        break;
  
      case 1: // 100ms after start of second -> end of timeframe for logic 0
        if (DCFpulse[sec] == dcf_0)
          digitalWrite(HAS_DCF77, dcf_high);
        break;
  
      case 2: // 200ms after start of second -> end of timeframe for logic 1
        digitalWrite(HAS_DCF77, dcf_high);
        break;
  
      case 9: // 900ms after start -> last pulse
        break;
  
      } // switch
  
      // pulse pause
      vTaskDelayUntil(&startTime, pdMS_TO_TICKS(DCF77_PULSE_LENGTH));
  
    } // for
  } // DCF77_Pulse()
  
  uint8_t *IRAM_ATTR DCF77_Frame(time_t const tt) {
  
    // array of dcf pulses for one minute, secs 0..16 and 20 are never touched, so
    // we keep them statically to avoid same recalculation every minute
  
    static uint8_t DCFpulse[DCF77_FRAME_SIZE + 1] = {
        dcf_0, dcf_0, dcf_0, dcf_0, dcf_0, dcf_0, dcf_0,
        dcf_0, dcf_0, dcf_0, dcf_0, dcf_0, dcf_0, dcf_0,
        dcf_0, dcf_0, dcf_0, dcf_0, dcf_0, dcf_0, dcf_1};
  
    uint8_t Parity;
    time_t t = myTZ.toLocal(tt); // convert to local time
  
    // ENCODE DST CHANGE ANNOUNCEMENT (Sec 16)
    DCFpulse[16] = dcf_0; // not yet implemented
  
    // ENCODE DAYLIGHTSAVING (secs 17..18)
    DCFpulse[17] = myTZ.locIsDST(t) ? dcf_1 : dcf_0;
    DCFpulse[18] = myTZ.locIsDST(t) ? dcf_0 : dcf_1;
  
    // ENCODE MINUTE (secs 21..28)
    Parity = dec2bcd(minute(t), 21, 27, DCFpulse);
    DCFpulse[28] = setParityBit(Parity);
  
    // ENCODE HOUR (secs 29..35)
    Parity = dec2bcd(hour(t), 29, 34, DCFpulse);
    DCFpulse[35] = setParityBit(Parity);
  
    // ENCODE DATE (secs 36..58)
    Parity = dec2bcd(day(t), 36, 41, DCFpulse);
    Parity += dec2bcd((weekday(t) - 1) ? (weekday(t) - 1) : 7, 42, 44, DCFpulse);
    Parity += dec2bcd(month(t), 45, 49, DCFpulse);
    Parity += dec2bcd(year(t) - 2000, 50, 57, DCFpulse);
    DCFpulse[58] = setParityBit(Parity);
  
    // ENCODE MARK (sec 59)
    DCFpulse[59] = dcf_Z; // !! missing code here for leap second !!
  
    // timestamp this frame with it's minute
    DCFpulse[60] = minute(t);
  
    return DCFpulse;
  
  } // DCF77_Frame()
  
  // helper function to convert decimal to bcd digit
  uint8_t IRAM_ATTR dec2bcd(uint8_t const dec, uint8_t const startpos,
                            uint8_t const endpos, uint8_t *DCFpulse) {
  
    uint8_t data = (dec < 10) ? dec : ((dec / 10) << 4) + (dec % 10);
    uint8_t parity = 0;
  
    for (uint8_t i = startpos; i <= endpos; i++) {
      DCFpulse[i] = (data & 1) ? dcf_1 : dcf_0;
      parity += (data & 1);
      data >>= 1;
    }
  
    return parity;
  }
  
  // helper function to encode parity
  uint8_t IRAM_ATTR setParityBit(uint8_t const p) {
    return ((p & 1) ? dcf_1 : dcf_0);
  }
  
  #endif // HAS_DCF77