JeeLabs Precision RTC Module

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exports = {};

var dstStatus = true;

function DS3231(_i2c) { this.i2c = _i2c; }

//private
var C = {
  i2c_address: 0x68,
  dateReg : 0x04,
  monthReg : 0x05,
  yearReg : 0x06,
  secsReg : 0x00,
  minsReg : 0x01,
  hourReg : 0x02,
  dowReg : 0x03
};

//private functions
// Convert Decimal value to BCD
function dec2bcd(val) {
  return parseInt(val, 16);
}

// Convert BCD value to decimal
function bcd2dec(val) {
  return ((val >> 4)*10+(val & 0x0F));
}

// Formatting
function format(val) {
  return ("0"+val).substr(-2);
}

//DST
function isDST(day,month,dow) {
  if ((month === 3) && (dow === 7) && (day > 23)) {
    return true;
  }
  if ((month === 10) && (dow === 7) && (day > 23)) {
    return false;
  }
  if ((month > 3) && (month < 11)) {
    return true;
  }
  else {
    return false;
  }
}

//public


//public functions
/* Put most of my comments outside the functions... */
DS3231.prototype.setDow = function(day) {
  var days = ["Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"];
  var idx = days.indexOf(day);
  if (idx<0) {
    print("Not a valid day");
  }
  else {
    this.i2c.writeTo(C.i2c_address,[C.dowReg, (dec2bcd(1+idx))]);
 }
};

DS3231.prototype.setDate = function(date,month,year) {
  this.i2c.writeTo(C.i2c_address,[C.dateReg, (dec2bcd(date))]);
  this.i2c.writeTo(C.i2c_address,[C.monthReg, (dec2bcd(month))]);
  this.i2c.writeTo(C.i2c_address,[C.yearReg, (dec2bcd(year))]);
  dstStatus = isDST(date,month,year);
};

DS3231.prototype.setTime = function(hour,minute) {
  this.i2c.writeTo(C.i2c_address,[C.secsReg, 0]);
  this.i2c.writeTo(C.i2c_address,[C.minsReg, (dec2bcd(minute))]);
  this.i2c.writeTo(C.i2c_address,[C.hourReg, (dec2bcd(hour))]);
};

DS3231.prototype.readDateTime = function () {
  this.i2c.writeTo(C.i2c_address, C.secsReg/* address*/);
  var data = this.i2c.readFrom(C.i2c_address, 7/* bytes */); //read number of bytes from address
  var seconds = bcd2dec(data[0]);
  var minutes = bcd2dec(data[1]);
  var hours = bcd2dec(data[2]);
  var dow = bcd2dec(data[3]);
  var date = bcd2dec(data[4]);
  var month = bcd2dec(data[5]);
  var year = bcd2dec(data[6]);
  
  //print(hours+" "+minutes+" "+seconds+" "+(isDST(date,month,dow))+" "+dstStatus);
  
  if (hours === 1 && minutes === 0 && seconds === 0 && isDST(date,month,dow) === true && dstStatus === false) { // clocks go forward
    this.i2c.writeTo(C.i2c_address,[C.hourReg, (dec2bcd(2))]);
    hours = 2;
    dstStatus = true;
  }
  
  if (hours === 2 && minutes === 0 && seconds === 0 && isDST(date,month,dow) === false && dstStatus === true) { // clocks go back
    this.i2c.writeTo(C.i2c_address,[C.hourReg, (dec2bcd(1))]);
    hours = 1;
    dstStatus = false;
  }
  
  var rtcDate = format(date)+"/"+format(month)+"/"+format(year);
  var rtcTime = format(hours)+":"+format(minutes)+":"+format(seconds);
  var rtcDateTime = rtcDate+" "+rtcTime;
  return rtcDateTime;
};

exports.connect = function(i2c) { return new DS3231(i2c); };

I2C1.setup({scl:B6,sda:B7});
var rtc = exports.connect(I2C1);