decoder.js

function Decoder(bytes, port) {
  // Decode an uplink message from a buffer
  // (array) of bytes to an object of fields.
  var decoded = {};

  if (bytes == null)
    return null;

  if (port === 1) {
    if (bytes.length != 11)
      return null;

    decoded.type = "position";

    decoded.latitudeDeg = bytes[0] + bytes[1] * 256 + bytes[2] * 65536 + bytes[3] * 16777216;
    if (decoded.latitudeDeg >= 0x80000000)
      decoded.latitudeDeg -= 0x100000000;
    decoded.latitudeDeg /= 1e7;

    decoded.longitudeDeg = bytes[4] + bytes[5] * 256 + bytes[6] * 65536 + bytes[7] * 16777216;
    if (decoded.longitudeDeg >= 0x80000000)
      decoded.longitudeDeg -= 0x100000000;
    decoded.longitudeDeg /= 1e7;

    decoded.inTrip = ((bytes[8] & 0x1) !== 0) ? true : false;
    decoded.fixFailed = ((bytes[8] & 0x2) !== 0) ? true : false;
    decoded.manDown = ((bytes[8] & 0x4) !== 0) ? true : false;

    decoded.headingDeg = (bytes[9] & 0x7) * 45;
    decoded.speedKmph = (bytes[9] >> 3) * 5;

    decoded.batV = bytes[10] * 0.025;
  }
  else if (port === 2) {
    if (bytes.length != 3)
      return null;

    decoded.type = "downlink ack";

    decoded.sequence = (bytes[0] & 0x7F);
    decoded.accepted = ((bytes[0] & 0x80) !== 0) ? true : false;
    decoded.fwMaj = bytes[1];
    decoded.fwMin = bytes[2];
  }
  else if (port === 3) {
    if (bytes.length != 11)
      return null;

    decoded.type = "stats";

    decoded.initialBatV = (((bytes[0] & 0xF) !== 0) ? (4.0 + (bytes[0] & 0xF) * 0.100) : null);
    decoded.txCount = 32 * ((bytes[0] >> 4) + (bytes[1] & 0x7F) * 16);
    decoded.tripCount = 32 * ((bytes[1] >> 7) + (bytes[2] & 0xFF) * 2
      + (bytes[3] & 0x0F) * 512);
    decoded.gpsSuccesses = 32 * ((bytes[3] >> 4) + (bytes[4] & 0x3F) * 16);
    decoded.gpsFails = 32 * ((bytes[4] >> 6) + (bytes[5] & 0x3F) * 4);
    decoded.aveGpsFixS = 1 * ((bytes[5] >> 6) + (bytes[6] & 0x7F) * 4);
    decoded.aveGpsFailS = 1 * ((bytes[6] >> 7) + (bytes[7] & 0xFF) * 2);
    decoded.aveGpsFreshenS = 1 * ((bytes[7] >> 8) + (bytes[8] & 0xFF) * 1);
    decoded.wakeupsPerTrip = 1 * ((bytes[8] >> 8) + (bytes[9] & 0x7F) * 1);
    decoded.uptimeWeeks = 1 * ((bytes[9] >> 7) + (bytes[10] & 0xFF) * 2);
  }
  return decoded;
}