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NMEA0183 parser object, implemented in ES script language

// MTK3333 NMEA custom packets extension
//
##require("NMEA183.ess");

// MTK chips && supported commands
//
enum MTK_DIRECTION
{
  IN  = 0;
  OUT = 1;
}

const c_MTK_CMDS = [
  // Command item is as follows:
  //[CMD, IN|OUT, FLD_COUNT, Descr]
  [ 
    3333,
    [
      [0,     MTK_DIRECTION$$OUT,   0,    "Test"],
      [1,     MTK_DIRECTION$$IN,    2,    "ACK response"],
      [220,   MTK_DIRECTION$$OUT,   1,    "Set POS fix rate"],
      [251,   MTK_DIRECTION$$OUT,   1,    "Set NMEA baudrate"],
      [300,   MTK_DIRECTION$$OUT,   5,    "Set fix control"],
      [314,   MTK_DIRECTION$$OUT,   19,   "Set NMEA sentence refresh intervals"],
      [330,   MTK_DIRECTION$$OUT,   1,    "Set datum"],
      [386,   MTK_DIRECTION$$OUT,   1,    "Set static navigation threshold"],
      [400,   MTK_DIRECTION$$OUT,   0,    "Fix control query"],
      [414,   MTK_DIRECTION$$OUT,   0,    "NMEA sentence refresh intervals query"],
      [430,   MTK_DIRECTION$$OUT,   0,    "Datum query"],
      [500,   MTK_DIRECTION$$IN,    5,    "Fix control data"],
      [514,   MTK_DIRECTION$$IN,    19,   "NMEA sentence refresh intervals"],
      [605,   MTK_DIRECTION$$OUT,   0,    "Firmware release info query"],
      [705,   MTK_DIRECTION$$IN,    4,    "Firmware release info"]
    ]
  ]
];

// NMEA0183 extensions for MTK platform
//
object EsNmeaMtk extends EsNmea0183
{
  var 
    m_chip,
    m_cmds;

  // Initialize commands available for the currently selected chip
  function commandsInit()
  var entry;
  {
    m_cmds = null;
    foreach(entry in c_MTK_CMDS)
    {
      if( m_chip == entry[0] )
      {
        m_cmds = entry[1];
        break;
      }
    }  
  }

  // Check if chip is supported
  function chipCheck(chip)
  var entry;
  {
    foreach(entry in c_MTK_CMDS)
    {
      if( chip == entry[0] )
        return;
    }
    
    throw EsStr::format("MTK Chip %d is not supported", chip);
  }
  
  // Check if command code is supported, requested direction is right,
  // and data filed count is as expected by the command
  //
  function cmdCheck(cmd, dir, data)
  var cmdEntry, fldCnt;
  {
    foreach(cmdEntry in m_cmds)
    {
      if( cmd == cmdEntry[0] )
      {
        if( dir != cmdEntry[1] )
          throw EsStr::format(
            "Wrong MTK command '%03d' direction.",
            cmd
          );
        
        fldCnt = cmdEntry[2];
        if( 0 == fldCnt && !data#isEmpty() )
          throw EsStr::format(
            "No data expected for MTK command '%03d'",
            cmd
          );
        else if( 0 < fldCnt )
        {
          if( data#isEmpty() )
            throw EsStr::format(
              "Expected %d data items for MTK command '%03d'",
              fldCnt,
              cmd
            );
          else if( fldCnt != data#countGet() )
            throw EsStr::format(
              "Expected %d data items for MTK command '%03d', got %d instead",
              fldCnt,
              cmd,
              data#countGet()
            );
        } 
        return;
      }
    }
    
    throw EsStr::format(
      "Unsupported MTK command '%03d' for chip '%d'",
      cmd,
      m_chip
    );
  }
  
  new(chip)
  {
    EsNmea0183::new();
    chipCheck(chip);
    m_chip = chip;
    commandsInit();
  }

  // Default ctor - use 3333 chip family by default
  new()
  {
    m_chip = 3333;
    commandsInit();
  }
  
  // Send proprietary packet to the MTK chip
  function cmdSend(chnl, cmd, data, withCrLf)
  {
    cmdCheck(cmd, MTK_DIRECTION$$OUT, data);
    return proprietarySend(
      chnl, 
      "MTK", 
      EsStr::format("%03u", cmd), 
      data,
      true, 
      withCrLf
    );
  }
  
  // Explicit formatting for special cmd 314 form
  function nmeaRefreshIntervalsReset(chnl, withCrLf)
  {
    return proprietarySend(
      chnl, 
      "MTK", 
      314, 
      [-1],
      true, 
      withCrLf
    );
  }
  
  // Properties
  //
  
  property chip;
  read: { return m_chip; }
  
  property commands;
  read: { return m_cmds; }
}

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