NRPN Parser in Javascript

nrpn_parser.js

var MAPPING = {
  
  // all messages on MSB 19
  18: {

    // message on LSB 0
    0: {
      "name": "FILT_1 FREQUENCY POT",
      "NRPN": true,
      "default": 250,
      "range": {
        "min": 0,
        "max": 65535
      }
    }

  },

  // all messages on MSB 19
  19: {

    // message on LSB 0
    0: {
      "name": "FILT_2 FREQUENCY POT",
      "NRPN": true,
      "default": 250,
      "range": {
        "min": 0,
        "max": 65535
      }
    }

  }
}

// MIDI CC constants
var CC_DATA_MSB = 6
var CC_DATA_LSB = 38

var CC_NRPN_LSB = 98
var CC_NRPN_MSB = 99

// inlets and outlets
inlets  = 1
outlets = 2

// hopefully recompile and reload
autowatch = true

// global variables and arrays
var nrpn_index
var value
var nrpn_index_lsb
var nrpn_index_msb = 0
var value_lsb
var value_msb = 0
var cc_index
var cc_value

// methods start here

// list - expects a CC Index + Value as argument
// filters out NRPN and RPN values and assigns to variables
// Passes through all other CCs
function list(val) {
	
  // we expect at least 2 arguments
  if (arguments.length != 2) return

  cc_index = arguments[0]
  cc_value = arguments[1]

  switch (cc_index) {
    case CC_DATA_MSB:
      // post("CC_DATA_MSB \n")

      // If we have a valid NRPN index, then the data is valid
      if (nrpn_index) {
        value_msb = cc_value << 7

        if (value_lsb) {
          value = value_msb | value_lsb
          // We are now ready to send an index and value out!
          send_nrpn(nrpn_index, value)
        }
      }
      // If we don't have an index it's invalid
      else {
        // So forward the value as a normal CC
        send_cc(cc_index, cc_value)
      }
      break

    case CC_DATA_LSB:
      // post("CC_DATA_LSB \n")
      // If we have a valid NRPN index, then the data is valid
      if (nrpn_index) {
        value_lsb = cc_value
        value = value_msb | value_lsb
        // We are now ready to send an index and value out!
        send_nrpn(nrpn_index, value)
      }
      // If we don't have an index it's invalid
      else {
        // So forward the value as a normal CC
        send_cc(cc_index, cc_value)
      }
      break

      // NRPN Index MSB - 7 high bits
    case CC_NRPN_MSB:
      // post("CC_NRPN_MSB \n")

      // Save 7 high bits
      nrpn_index_msb = cc_value << 7

      // Create the 14 bit NRPN index
      nrpn_index = nrpn_index_msb | nrpn_index_lsb

      post_name( nrpn_index_msb, nrpn_index_lsb )

      break
      // NRPN Index LSB - 7 low bits

    case CC_NRPN_LSB:
      // post("CC_NRPN_LSB \n")

      // Save 7 low bits
      nrpn_index_lsb = cc_value

      // Create the 14 bit NRPN index
      nrpn_index = nrpn_index_msb | nrpn_index_lsb

      post_name( nrpn_index_msb, nrpn_index_lsb )

      break

    default:
      send_cc(cc_index, cc_value)
      break
  }
}

function post_name( MSB, LSB ) {

  // sometimes it seems LSB comes as undefined
  LSB = LSB || 0

  // Divide by 128 to get the actual CTRL #
  MSB = MSB >> 7

  // selected parameter map
  var param

  post("\n")

  if( MAPPING[MSB] && MAPPING[MSB][LSB] ) {

    param = MAPPING[MSB][LSB]

    post( "SELECTED PARAM: " )
    post( "\n")
    post( param.name )
    post( "\n")
    post( "RANGE MIN: " + param.range.min )
    post( "\n")
    post( "RANGE MAX: " + ( ( param.range.max + 1 ) / 16 ) )
  }

  post("\n")

}

// Send CC: Forward CC index and value to output 0
function send_cc(i, v) {
  outlet(0, i, v)
}

// Send NRPN: Send NRPN index and value to output 1
function send_nrpn(NRPN, VALUE) {

  // correct output
  // outlet(1, NRPN >> 7, NRPN % 128, VALUE)
  outlet(1, VALUE, NRPN % 128, NRPN >> 7)


  value = null // reset the parsed value
  value_lsb = null // reset the LSB of the value
}