text: var Emitter = require("events").EventEmitter;
  var shared;
  
  function Bank(options) {
    this.address = options.address;
    this.io = options.io;
    this.io.i2cConfig(options);
  }
  
  Bank.prototype.read = function(register, numBytes, callback) {
    if (register) {
      this.io.i2cRead(this.address, register, numBytes, callback);
    } else {
      this.io.i2cRead(this.address, numBytes, callback);
    }
  };
  
  Bank.prototype.write = function(register, bytes) {
    if (!Array.isArray(bytes)) {
      bytes = [bytes];
    }
    this.io.i2cWrite(this.address, register, bytes);
  };
  
  // http://www.nr.edu/csc200/labs-ev3/ev3-user-guide-EN.pdf
  
  function EVS(options) {
    if (shared) {
      return shared;
    }
  
    this.bank = {
      a: new Bank({
        address: EVS.BANK_A,
        io: options.io,
      }),
      b: new Bank({
        address: EVS.BANK_B,
        io: options.io,
      })
    };
  
    shared = this;
  }
  
  EVS.shieldPort = function(pin) {
    var port = EVS[pin];
  
    if (port === undefined) {
      throw new Error("Invalid EVShield pin name");
    }
  
    var address, analog, bank, motor, mode, offset, sensor;
    var endsWithS1 = false;
  
    if (pin.startsWith("BA")) {
      address = EVS.BANK_A;
      bank = "a";
    } else {
      address = EVS.BANK_B;
      bank = "b";
    }
  
    if (pin.includes("M")) {
      motor = pin.endsWith("M1") ? EVS.S1 : EVS.S2;
    }
  
    if (pin.includes("S")) {
      endsWithS1 = pin.endsWith("S1");
  
      // Used for reading 2 byte integer values from raw sensors
      analog = endsWithS1 ? EVS.S1_ANALOG : EVS.S2_ANALOG;
      // Sensor Mode (1 or 2?)
      mode = endsWithS1 ? EVS.S1_MODE : EVS.S2_MODE;
      // Used for read registers
      offset = endsWithS1 ? EVS.S1_OFFSET : EVS.S2_OFFSET;
      // Used to address "sensor type"
      sensor = endsWithS1 ? EVS.S1 : EVS.S2;
    }
  
    return {
      address: address,
      analog: analog,
      bank: bank,
      mode: mode,
      motor: motor,
      offset: offset,
      port: port,
      sensor: sensor,
    };
  };
  
  EVS.isRawSensor = function(port) {
    return port.analog === EVS.S1_ANALOG || port.analog === EVS.S2_ANALOG;
  };
  
  EVS.prototype = Object.create(Emitter.prototype, {
    constructor: {
      value: EVS
    }
  });
  
  EVS.prototype.setup = function(port, type) {
    this.bank[port.bank].write(port.mode, [type]);
  };
  
  EVS.prototype.read = function(port, register, numBytes, callback) {
  
    if (port.sensor && port.offset && !EVS.isRawSensor(port)) {
      register += port.offset;
    }
  
    this.bank[port.bank].read(register, numBytes, callback);
  };
  
  EVS.prototype.write = function(port, register, data) {
    this.bank[port.bank].write(register, data);
  };
  
  /*
   * Shield Registers
   */
  
  EVS.BAS1 = 0x01;
  EVS.BAS2 = 0x02;
  EVS.BBS1 = 0x03;
  EVS.BBS2 = 0x04;
  
  EVS.BAM1 = 0x05;
  EVS.BAM2 = 0x06;
  EVS.BBM1 = 0x07;
  EVS.BBM2 = 0x08;
  
  EVS.BANK_A = 0x1A;
  EVS.BANK_B = 0x1B;
  
  EVS.S1 = 0x01;
  EVS.S2 = 0x02;
  
  EVS.M1 = 0x01;
  EVS.M2 = 0x02;
  EVS.MM = 0x03;
  
  EVS.Type_NONE = 0x00;
  EVS.Type_SWITCH = 0x01;
  EVS.Type_ANALOG = 0x02;
  
  EVS.Type_I2C = 0x09;
  
  /*
   * Sensor Mode NXT
   */
  EVS.Type_NXT_LIGHT_REFLECTED = 0x03;
  EVS.Type_NXT_LIGHT = 0x04;
  EVS.Type_NXT_COLOR = 0x0D;
  EVS.Type_NXT_COLOR_RGBRAW = 0x04;
  EVS.Type_NXT_COLORRED = 0x0E;
  EVS.Type_NXT_COLORGREEN = 0x0F;
  EVS.Type_NXT_COLORBLUE = 0x10;
  EVS.Type_NXT_COLORNONE = 0x11;
  
  
  EVS.Type_DATABIT0_HIGH = 0x40;
  
  /*
   * Sensor Port Controls
   */
  EVS.S1_MODE = 0x6F;
  // EVS.S1_EV3_MODE = 0x6F;
  EVS.S1_ANALOG = 0x70;
  EVS.S1_OFFSET = 0;
  
  EVS.S2_MODE = 0xA3;
  // EVS.S2_EV3_MODE = 0x6F;
  EVS.S2_ANALOG = 0xA4;
  EVS.S2_OFFSET = 52;
  
  /*
   * Sensor Mode EV3
   */
  EVS.Type_EV3_LIGHT_REFLECTED = 0x00;
  EVS.Type_EV3_LIGHT = 0x01;
  EVS.Type_EV3_COLOR = 0x02;
  EVS.Type_EV3_COLOR_REFRAW = 0x03;
  EVS.Type_EV3_COLOR_RGBRAW = 0x04;
  EVS.Type_EV3_TOUCH = 0x12;
  EVS.Type_EV3 = 0x13;
  
  /*
   * Sensor Read Registers
   */
  EVS.Light = 0x83;
  EVS.Bump = 0x84;
  EVS.ColorMeasure = 0x83;
  EVS.Proximity = 0x83;
  EVS.Touch = 0x83;
  EVS.Ultrasonic = 0x81;
  EVS.Mode = 0x81;
  
  /*
   * Sensor Read Byte Counts
   */
  EVS.Light_Bytes = 2;
  EVS.Analog_Bytes = 2;
  EVS.Bump_Bytes = 1;
  EVS.ColorMeasure_Bytes = 2;
  EVS.Proximity_Bytes = 2;
  EVS.Touch_Bytes = 1;
  
  
  /*
   * Motor selection
   */
  EVS.Motor_1 = 0x01;
  EVS.Motor_2 = 0x02;
  EVS.Motor_Both = 0x03;
  
  /*
   * Motor next action
   */
  // stop and let the motor coast.
  EVS.Motor_Next_Action_Float = 0x00;
  // apply brakes, and resist change to tachometer, but if tach position is forcibly changed, do not restore position
  EVS.Motor_Next_Action_Brake = 0x01;
  // apply brakes, and restore externally forced change to tachometer
  EVS.Motor_Next_Action_BrakeHold = 0x02;
  
  EVS.Motor_Stop = 0x60;
  EVS.Motor_Reset = 0x52;
  
  /*
   * Motor direction
   */
  
  EVS.Motor_Reverse = 0x00;
  EVS.Motor_Forward = 0x01;
  
  /*
   * Motor Tachometer movement
   */
  
  // Move the tach to absolute value provided
  EVS.Motor_Move_Absolute = 0x00;
  // Move the tach relative to previous position
  EVS.Motor_Move_Relative = 0x01;
  
  /*
   * Motor completion
   */
  
  EVS.Motor_Completion_Dont_Wait = 0x00;
  EVS.Motor_Completion_Wait_For = 0x01;
  
  /*
   * 0-100
   */
  EVS.Speed_Full = 90;
  EVS.Speed_Medium = 60;
  EVS.Speed_Slow = 25;
  
  /*
   * Motor Port Controls
   */
  EVS.CONTROL_SPEED = 0x01;
  EVS.CONTROL_RAMP = 0x02;
  EVS.CONTROL_RELATIVE = 0x04;
  EVS.CONTROL_TACHO = 0x08;
  EVS.CONTROL_BRK = 0x10;
  EVS.CONTROL_ON = 0x20;
  EVS.CONTROL_TIME = 0x40;
  EVS.CONTROL_GO = 0x80;
  
  EVS.STATUS_SPEED = 0x01;
  EVS.STATUS_RAMP = 0x02;
  EVS.STATUS_MOVING = 0x04;
  EVS.STATUS_TACHO = 0x08;
  EVS.STATUS_BREAK = 0x10;
  EVS.STATUS_OVERLOAD = 0x20;
  EVS.STATUS_TIME = 0x40;
  EVS.STATUS_STALL = 0x80;
  
  EVS.COMMAND = 0x41;
  EVS.VOLTAGE = 0x6E;
  
  EVS.SETPT_M1 = 0x42;
  EVS.SPEED_M1 = 0x46;
  EVS.TIME_M1 = 0x47;
  EVS.CMD_B_M1 = 0x48;
  EVS.CMD_A_M1 = 0x49;
  
  EVS.SETPT_M2 = 0x4A;
  EVS.SPEED_M2 = 0x4E;
  EVS.TIME_M2 = 0x4F;
  EVS.CMD_B_M2 = 0x50;
  EVS.CMD_A_M2 = 0x51;
  
  
  /*
   * Motor Read registers.
   */
  EVS.POSITION_M1 = 0x52;
  EVS.POSITION_M2 = 0x56;
  EVS.STATUS_M1 = 0x5A;
  EVS.STATUS_M2 = 0x5B;
  EVS.TASKS_M1 = 0x5C;
  EVS.TASKS_M2 = 0x5D;
  
  EVS.ENCODER_PID = 0x5E;
  EVS.SPEED_PID = 0x64;
  EVS.PASS_COUNT = 0x6A;
  EVS.TOLERANCE = 0x6B;
  
  /*
   * Built-in components
   */
  EVS.BTN_PRESS = 0xDA;
  EVS.RGB_LED = 0xD7;
  EVS.CENTER_RGB_LED = 0xDE;
  
  
  
  module.exports = EVS;
  