text: /***************************************************************************
    This is a library for the BNO055 orientation sensor
  
    Designed specifically to work with the Adafruit BNO055 Breakout.
  
    Pick one up today in the adafruit shop!
    ------> http://www.adafruit.com/products
  
    These sensors use I2C to communicate, 2 pins are required to interface.
  
    Adafruit invests time and resources providing this open source code,
    please support Adafruit andopen-source hardware by purchasing products
    from Adafruit!
  
    Written by KTOWN for Adafruit Industries.
  
    MIT license, all text above must be included in any redistribution
   ***************************************************************************/
  
  #if ARDUINO >= 100
   #include "Arduino.h"
  #else
   #include "WProgram.h"
  #endif
  
  #include <math.h>
  #include <limits.h>
  
  #include "Adafruit_BNO055.h"
  
  /***************************************************************************
   CONSTRUCTOR
   ***************************************************************************/
  
  /**************************************************************************/
  /*!
      @brief  Instantiates a new Adafruit_BNO055 class
  */
  /**************************************************************************/
  Adafruit_BNO055::Adafruit_BNO055(int32_t sensorID, uint8_t address)
  {
    _sensorID = sensorID;
    _address = address;
  }
  
  /***************************************************************************
   PUBLIC FUNCTIONS
   ***************************************************************************/
  
  /**************************************************************************/
  /*!
      @brief  Sets up the HW
  */
  /**************************************************************************/
  bool Adafruit_BNO055::begin(adafruit_bno055_opmode_t mode)
  {
    /* Enable I2C */
    
  #ifndef ESP8266
    Wire.begin();
  #else
    Serial.print("Starting I2C: SDA: ");
    Serial.print(_sda);
    Serial.print(" SCL: ");
    Serial.print(_scl);
    Serial.print(" clock Stretch Limit: ");
    Serial.print(_clockStretchLimit);
    Serial.println("");
    Serial.flush();
    
    Wire.begin(_sda,_scl);
    
    if ( _clockStretchLimit != 0 ) {
      Wire.setClockStretchLimit(_clockStretchLimit);
    }
  #endif
  
    /* Make sure we have the right device */
    uint8_t id = read8(BNO055_CHIP_ID_ADDR);
    if(id != BNO055_ID)
    {
  #ifdef ESP8266
      Serial.print("Got wrong ID. Expected: ");
      Serial.print(BNO055_ID);
      Serial.print(" Got : ");
      Serial.print(id);
      Serial.println(". rebooting");
      Serial.flush();
  #endif
  
      delay(1000); // hold on for boot
      id = read8(BNO055_CHIP_ID_ADDR);
      if(id != BNO055_ID) {
  #ifdef ESP8266
        Serial.print("Got wrong ID again. Expected: ");
        Serial.print(BNO055_ID);
        Serial.print(" Got : ");
        Serial.print(id);
        Serial.println(". returning false");
        Serial.flush();
  #endif
        return false;  // still not? ok bail
      }
    }
  
    /* Switch to config mode (just in case since this is the default) */
    setMode(OPERATION_MODE_CONFIG);
  
    /* Reset */
    write8(BNO055_SYS_TRIGGER_ADDR, 0x20);
    while (read8(BNO055_CHIP_ID_ADDR) != BNO055_ID)
    {
      delay(10);
    }
    delay(50);
  
    /* Set to normal power mode */
    write8(BNO055_PWR_MODE_ADDR, POWER_MODE_NORMAL);
    delay(10);
  
    write8(BNO055_PAGE_ID_ADDR, 0);
  
    /* Set the output units */
    /*
    uint8_t unitsel = (0 << 7) | // Orientation = Android
                      (0 << 4) | // Temperature = Celsius
                      (0 << 2) | // Euler = Degrees
                      (1 << 1) | // Gyro = Rads
                      (0 << 0);  // Accelerometer = m/s^2
    write8(BNO055_UNIT_SEL_ADDR, unitsel);
    */
  
    /* Configure axis mapping (see section 3.4) */
    /*
    write8(BNO055_AXIS_MAP_CONFIG_ADDR, REMAP_CONFIG_P2); // P0-P7, Default is P1
    delay(10);
    write8(BNO055_AXIS_MAP_SIGN_ADDR, REMAP_SIGN_P2); // P0-P7, Default is P1
    delay(10);
    */
    
    write8(BNO055_SYS_TRIGGER_ADDR, 0x0);
    delay(10);
    /* Set the requested operating mode (see section 3.3) */
    setMode(mode);
    delay(20);
  
    return true;
  }
  
  #ifdef ESP8266
  void Adafruit_BNO055::setPorts             ( int sda, int scl ) {
    _sda = sda;
    _scl = scl;
  }
  void  Adafruit_BNO055::setClockStretchLimit( int clockStretchLimit ) {
    _clockStretchLimit = clockStretchLimit;
  }
  #endif
  /**************************************************************************/
  /*!
      @brief  Puts the chip in the specified operating mode
  */
  /**************************************************************************/
  void Adafruit_BNO055::setMode(adafruit_bno055_opmode_t mode)
  {
    _mode = mode;
    write8(BNO055_OPR_MODE_ADDR, _mode);
    delay(30);
  }
  
  /**************************************************************************/
  /*!
      @brief  Use the external 32.768KHz crystal
  */
  /**************************************************************************/
  void Adafruit_BNO055::setExtCrystalUse(boolean usextal)
  {
    adafruit_bno055_opmode_t modeback = _mode;
  
    /* Switch to config mode (just in case since this is the default) */
    setMode(OPERATION_MODE_CONFIG);
    delay(25);
    write8(BNO055_PAGE_ID_ADDR, 0);
    if (usextal) {
      write8(BNO055_SYS_TRIGGER_ADDR, 0x80);
    } else {
      write8(BNO055_SYS_TRIGGER_ADDR, 0x00);
    }
    delay(10);
    /* Set the requested operating mode (see section 3.3) */
    setMode(modeback);
    delay(20);
  }
  
  
  /**************************************************************************/
  /*!
      @brief  Gets the latest system status info
  */
  /**************************************************************************/
  void Adafruit_BNO055::getSystemStatus(uint8_t *system_status, uint8_t *self_test_result, uint8_t *system_error)
  {
    write8(BNO055_PAGE_ID_ADDR, 0);
  
    /* System Status (see section 4.3.58)
       ---------------------------------
       0 = Idle
       1 = System Error
       2 = Initializing Peripherals
       3 = System Iniitalization
       4 = Executing Self-Test
       5 = Sensor fusio algorithm running
       6 = System running without fusion algorithms */
  
    if (system_status != 0)
      *system_status    = read8(BNO055_SYS_STAT_ADDR);
  
    /* Self Test Results (see section )
       --------------------------------
       1 = test passed, 0 = test failed
  
       Bit 0 = Accelerometer self test
       Bit 1 = Magnetometer self test
       Bit 2 = Gyroscope self test
       Bit 3 = MCU self test
  
       0x0F = all good! */
  
    if (self_test_result != 0)
      *self_test_result = read8(BNO055_SELFTEST_RESULT_ADDR);
  
    /* System Error (see section 4.3.59)
       ---------------------------------
       0 = No error
       1 = Peripheral initialization error
       2 = System initialization error
       3 = Self test result failed
       4 = Register map value out of range
       5 = Register map address out of range
       6 = Register map write error
       7 = BNO low power mode not available for selected operat ion mode
       8 = Accelerometer power mode not available
       9 = Fusion algorithm configuration error
       A = Sensor configuration error */
  
    if (system_error != 0)
      *system_error     = read8(BNO055_SYS_ERR_ADDR);
  
    delay(200);
  }
  
  /**************************************************************************/
  /*!
      @brief  Gets the chip revision numbers
  */
  /**************************************************************************/
  void Adafruit_BNO055::getRevInfo(adafruit_bno055_rev_info_t* info)
  {
    uint8_t a, b;
  
    memset(info, 0, sizeof(adafruit_bno055_rev_info_t));
  
    /* Check the accelerometer revision */
    info->accel_rev = read8(BNO055_ACCEL_REV_ID_ADDR);
  
    /* Check the magnetometer revision */
    info->mag_rev   = read8(BNO055_MAG_REV_ID_ADDR);
  
    /* Check the gyroscope revision */
    info->gyro_rev  = read8(BNO055_GYRO_REV_ID_ADDR);
  
    /* Check the SW revision */
    info->bl_rev    = read8(BNO055_BL_REV_ID_ADDR);
  
    a = read8(BNO055_SW_REV_ID_LSB_ADDR);
    b = read8(BNO055_SW_REV_ID_MSB_ADDR);
    info->sw_rev = (((uint16_t)b) << 8) | ((uint16_t)a);
  }
  
  /**************************************************************************/
  /*!
      @brief  Gets current calibration state.  Each value should be a uint8_t
              pointer and it will be set to 0 if not calibrated and 3 if
              fully calibrated.
  */
  /**************************************************************************/
  void Adafruit_BNO055::getCalibration(uint8_t* sys, uint8_t* gyro, uint8_t* accel, uint8_t* mag) {
    uint8_t calData = read8(BNO055_CALIB_STAT_ADDR);
    if (sys != NULL) {
      *sys = (calData >> 6) & 0x03;
    }
    if (gyro != NULL) {
      *gyro = (calData >> 4) & 0x03;
    }
    if (accel != NULL) {
      *accel = (calData >> 2) & 0x03;
    }
    if (mag != NULL) {
      *mag = calData & 0x03;
    }
  }
  
  /**************************************************************************/
  /*!
      @brief  Gets the temperature in degrees celsius
  */
  /**************************************************************************/
  int8_t Adafruit_BNO055::getTemp(void)
  {
    int8_t temp = (int8_t)(read8(BNO055_TEMP_ADDR));
    return temp;
  }
  
  /**************************************************************************/
  /*!
      @brief  Gets a vector reading from the specified source
  */
  /**************************************************************************/
  imu::Vector<3> Adafruit_BNO055::getVector(adafruit_vector_type_t vector_type)
  {
    imu::Vector<3> xyz;
    uint8_t buffer[6];
    memset (buffer, 0, 6);
  
    int16_t x, y, z;
    x = y = z = 0;
  
    /* Read vector data (6 bytes) */
    readLen((adafruit_bno055_reg_t)vector_type, buffer, 6);
  
    x = ((int16_t)buffer[0]) | (((int16_t)buffer[1]) << 8);
    y = ((int16_t)buffer[2]) | (((int16_t)buffer[3]) << 8);
    z = ((int16_t)buffer[4]) | (((int16_t)buffer[5]) << 8);
  
    /* Convert the value to an appropriate range (section 3.6.4) */
    /* and assign the value to the Vector type */
    switch(vector_type)
    {
      case VECTOR_MAGNETOMETER:
        /* 1uT = 16 LSB */
        xyz[0] = ((double)x)/16.0;
        xyz[1] = ((double)y)/16.0;
        xyz[2] = ((double)z)/16.0;
        break;
      case VECTOR_GYROSCOPE:
        /* 1rps = 900 LSB */
        xyz[0] = ((double)x)/900.0;
        xyz[1] = ((double)y)/900.0;
        xyz[2] = ((double)z)/900.0;
        break;
      case VECTOR_EULER:
        /* 1 degree = 16 LSB */
        xyz[0] = ((double)x)/16.0;
        xyz[1] = ((double)y)/16.0;
        xyz[2] = ((double)z)/16.0;
        break;
      case VECTOR_ACCELEROMETER:
      case VECTOR_LINEARACCEL:
      case VECTOR_GRAVITY:
        /* 1m/s^2 = 100 LSB */
        xyz[0] = ((double)x)/100.0;
        xyz[1] = ((double)y)/100.0;
        xyz[2] = ((double)z)/100.0;
        break;
    }
  
    return xyz;
  }
  
  /**************************************************************************/
  /*!
      @brief  Gets a quaternion reading from the specified source
  */
  /**************************************************************************/
  imu::Quaternion Adafruit_BNO055::getQuat(void)
  {
    uint8_t buffer[8];
    memset (buffer, 0, 8);
  
    int16_t x, y, z, w;
    x = y = z = w = 0;
  
    /* Read quat data (8 bytes) */
    readLen(BNO055_QUATERNION_DATA_W_LSB_ADDR, buffer, 8);
    w = (((uint16_t)buffer[1]) << 8) | ((uint16_t)buffer[0]);
    x = (((uint16_t)buffer[3]) << 8) | ((uint16_t)buffer[2]);
    y = (((uint16_t)buffer[5]) << 8) | ((uint16_t)buffer[4]);
    z = (((uint16_t)buffer[7]) << 8) | ((uint16_t)buffer[6]);
  
    /* Assign to Quaternion */
    /* See http://ae-bst.resource.bosch.com/media/products/dokumente/bno055/BST_BNO055_DS000_12~1.pdf
       3.6.5.5 Orientation (Quaternion)  */
    const double scale = (1.0 / (1<<14));
    imu::Quaternion quat(scale * w, scale * x, scale * y, scale * z);
    return quat;
  }
  
  /**************************************************************************/
  /*!
      @brief  Provides the sensor_t data for this sensor
  */
  /**************************************************************************/
  void Adafruit_BNO055::getSensor(sensor_t *sensor)
  {
    /* Clear the sensor_t object */
    memset(sensor, 0, sizeof(sensor_t));
  
    /* Insert the sensor name in the fixed length char array */
    strncpy (sensor->name, "BNO055", sizeof(sensor->name) - 1);
    sensor->name[sizeof(sensor->name)- 1] = 0;
    sensor->version     = 1;
    sensor->sensor_id   = _sensorID;
    sensor->type        = SENSOR_TYPE_ORIENTATION;
    sensor->min_delay   = 0;
    sensor->max_value   = 0.0F;
    sensor->min_value   = 0.0F;
    sensor->resolution  = 0.01F;
  }
  
  /**************************************************************************/
  /*!
      @brief  Reads the sensor and returns the data as a sensors_event_t
  */
  /**************************************************************************/
  bool Adafruit_BNO055::getEvent(sensors_event_t *event)
  {
    /* Clear the event */
    memset(event, 0, sizeof(sensors_event_t));
  
    event->version   = sizeof(sensors_event_t);
    event->sensor_id = _sensorID;
    event->type      = SENSOR_TYPE_ORIENTATION;
    event->timestamp = millis();
  
    /* Get a Euler angle sample for orientation */
    imu::Vector<3> euler = getVector(Adafruit_BNO055::VECTOR_EULER);
    event->orientation.x = euler.x();
    event->orientation.y = euler.y();
    event->orientation.z = euler.z();
  
    return true;
  }
  
  /**************************************************************************/
  /*!
  @brief  Reads the sensor's offset registers into a byte array
  */
  /**************************************************************************/
  bool Adafruit_BNO055::getSensorOffsets(uint8_t* calibData)
  {
      if (isFullyCalibrated())
      {
          adafruit_bno055_opmode_t lastMode = _mode;
          setMode(OPERATION_MODE_CONFIG);
  
          readLen(ACCEL_OFFSET_X_LSB_ADDR, calibData, NUM_BNO055_OFFSET_REGISTERS);
  
          setMode(lastMode);
          return true;
      }
      return false;
  }
  
  /**************************************************************************/
  /*!
  @brief  Reads the sensor's offset registers into an offset struct
  */
  /**************************************************************************/
  bool Adafruit_BNO055::getSensorOffsets(adafruit_bno055_offsets_t &offsets_type)
  {
      if (isFullyCalibrated())
      {
          adafruit_bno055_opmode_t lastMode = _mode;
          setMode(OPERATION_MODE_CONFIG);
          delay(25);
  
          offsets_type.accel_offset_x = (read8(ACCEL_OFFSET_X_MSB_ADDR) << 8) | (read8(ACCEL_OFFSET_X_LSB_ADDR));
          offsets_type.accel_offset_y = (read8(ACCEL_OFFSET_Y_MSB_ADDR) << 8) | (read8(ACCEL_OFFSET_Y_LSB_ADDR));
          offsets_type.accel_offset_z = (read8(ACCEL_OFFSET_Z_MSB_ADDR) << 8) | (read8(ACCEL_OFFSET_Z_LSB_ADDR));
  
          offsets_type.gyro_offset_x = (read8(GYRO_OFFSET_X_MSB_ADDR) << 8) | (read8(GYRO_OFFSET_X_LSB_ADDR));
          offsets_type.gyro_offset_y = (read8(GYRO_OFFSET_Y_MSB_ADDR) << 8) | (read8(GYRO_OFFSET_Y_LSB_ADDR));
          offsets_type.gyro_offset_z = (read8(GYRO_OFFSET_Z_MSB_ADDR) << 8) | (read8(GYRO_OFFSET_Z_LSB_ADDR));
  
          offsets_type.mag_offset_x = (read8(MAG_OFFSET_X_MSB_ADDR) << 8) | (read8(MAG_OFFSET_X_LSB_ADDR));
          offsets_type.mag_offset_y = (read8(MAG_OFFSET_Y_MSB_ADDR) << 8) | (read8(MAG_OFFSET_Y_LSB_ADDR));
          offsets_type.mag_offset_z = (read8(MAG_OFFSET_Z_MSB_ADDR) << 8) | (read8(MAG_OFFSET_Z_LSB_ADDR));
  
          offsets_type.accel_radius = (read8(ACCEL_RADIUS_MSB_ADDR) << 8) | (read8(ACCEL_RADIUS_LSB_ADDR));
          offsets_type.mag_radius = (read8(MAG_RADIUS_MSB_ADDR) << 8) | (read8(MAG_RADIUS_LSB_ADDR));
  
          setMode(lastMode);
          return true;
      }
      return false;
  }
  
  
  /**************************************************************************/
  /*!
  @brief  Writes an array of calibration values to the sensor's offset registers
  */
  /**************************************************************************/
  void Adafruit_BNO055::setSensorOffsets(const uint8_t* calibData)
  {
      adafruit_bno055_opmode_t lastMode = _mode;
      setMode(OPERATION_MODE_CONFIG);
      delay(25);
  
      /* A writeLen() would make this much cleaner */
      write8(ACCEL_OFFSET_X_LSB_ADDR, calibData[0]);
      write8(ACCEL_OFFSET_X_MSB_ADDR, calibData[1]);
      write8(ACCEL_OFFSET_Y_LSB_ADDR, calibData[2]);
      write8(ACCEL_OFFSET_Y_MSB_ADDR, calibData[3]);
      write8(ACCEL_OFFSET_Z_LSB_ADDR, calibData[4]);
      write8(ACCEL_OFFSET_Z_MSB_ADDR, calibData[5]);
  
      write8(GYRO_OFFSET_X_LSB_ADDR, calibData[6]);
      write8(GYRO_OFFSET_X_MSB_ADDR, calibData[7]);
      write8(GYRO_OFFSET_Y_LSB_ADDR, calibData[8]);
      write8(GYRO_OFFSET_Y_MSB_ADDR, calibData[9]);
      write8(GYRO_OFFSET_Z_LSB_ADDR, calibData[10]);
      write8(GYRO_OFFSET_Z_MSB_ADDR, calibData[11]);
  
      write8(MAG_OFFSET_X_LSB_ADDR, calibData[12]);
      write8(MAG_OFFSET_X_MSB_ADDR, calibData[13]);
      write8(MAG_OFFSET_Y_LSB_ADDR, calibData[14]);
      write8(MAG_OFFSET_Y_MSB_ADDR, calibData[15]);
      write8(MAG_OFFSET_Z_LSB_ADDR, calibData[16]);
      write8(MAG_OFFSET_Z_MSB_ADDR, calibData[17]);
  
      write8(ACCEL_RADIUS_LSB_ADDR, calibData[18]);
      write8(ACCEL_RADIUS_MSB_ADDR, calibData[19]);
  
      write8(MAG_RADIUS_LSB_ADDR, calibData[20]);
      write8(MAG_RADIUS_MSB_ADDR, calibData[21]);
  
      setMode(lastMode);
  }
  
  /**************************************************************************/
  /*!
  @brief  Writes to the sensor's offset registers from an offset struct
  */
  /**************************************************************************/
  void Adafruit_BNO055::setSensorOffsets(const adafruit_bno055_offsets_t &offsets_type)
  {
      adafruit_bno055_opmode_t lastMode = _mode;
      setMode(OPERATION_MODE_CONFIG);
      delay(25);
  
      write8(ACCEL_OFFSET_X_LSB_ADDR, (offsets_type.accel_offset_x) & 0x0FF);
      write8(ACCEL_OFFSET_X_MSB_ADDR, (offsets_type.accel_offset_x >> 8) & 0x0FF);
      write8(ACCEL_OFFSET_Y_LSB_ADDR, (offsets_type.accel_offset_y) & 0x0FF);
      write8(ACCEL_OFFSET_Y_MSB_ADDR, (offsets_type.accel_offset_y >> 8) & 0x0FF);
      write8(ACCEL_OFFSET_Z_LSB_ADDR, (offsets_type.accel_offset_z) & 0x0FF);
      write8(ACCEL_OFFSET_Z_MSB_ADDR, (offsets_type.accel_offset_z >> 8) & 0x0FF);
  
      write8(GYRO_OFFSET_X_LSB_ADDR, (offsets_type.gyro_offset_x) & 0x0FF);
      write8(GYRO_OFFSET_X_MSB_ADDR, (offsets_type.gyro_offset_x >> 8) & 0x0FF);
      write8(GYRO_OFFSET_Y_LSB_ADDR, (offsets_type.gyro_offset_y) & 0x0FF);
      write8(GYRO_OFFSET_Y_MSB_ADDR, (offsets_type.gyro_offset_y >> 8) & 0x0FF);
      write8(GYRO_OFFSET_Z_LSB_ADDR, (offsets_type.gyro_offset_z) & 0x0FF);
      write8(GYRO_OFFSET_Z_MSB_ADDR, (offsets_type.gyro_offset_z >> 8) & 0x0FF);
  
      write8(MAG_OFFSET_X_LSB_ADDR, (offsets_type.mag_offset_x) & 0x0FF);
      write8(MAG_OFFSET_X_MSB_ADDR, (offsets_type.mag_offset_x >> 8) & 0x0FF);
      write8(MAG_OFFSET_Y_LSB_ADDR, (offsets_type.mag_offset_y) & 0x0FF);
      write8(MAG_OFFSET_Y_MSB_ADDR, (offsets_type.mag_offset_y >> 8) & 0x0FF);
      write8(MAG_OFFSET_Z_LSB_ADDR, (offsets_type.mag_offset_z) & 0x0FF);
      write8(MAG_OFFSET_Z_MSB_ADDR, (offsets_type.mag_offset_z >> 8) & 0x0FF);
  
      write8(ACCEL_RADIUS_LSB_ADDR, (offsets_type.accel_radius) & 0x0FF);
      write8(ACCEL_RADIUS_MSB_ADDR, (offsets_type.accel_radius >> 8) & 0x0FF);
  
      write8(MAG_RADIUS_LSB_ADDR, (offsets_type.mag_radius) & 0x0FF);
      write8(MAG_RADIUS_MSB_ADDR, (offsets_type.mag_radius >> 8) & 0x0FF);
  
      setMode(lastMode);
  }
  
  bool Adafruit_BNO055::isFullyCalibrated(void)
  {
      uint8_t system, gyro, accel, mag;
      getCalibration(&system, &gyro, &accel, &mag);
      if (system < 3 || gyro < 3 || accel < 3 || mag < 3)
          return false;
      return true;
  }
  
  
  /***************************************************************************
   PRIVATE FUNCTIONS
   ***************************************************************************/
  
  /**************************************************************************/
  /*!
      @brief  Writes an 8 bit value over I2C
  */
  /**************************************************************************/
  bool Adafruit_BNO055::write8(adafruit_bno055_reg_t reg, byte value)
  {
    Wire.beginTransmission(_address);
    #if ARDUINO >= 100
      Wire.write((uint8_t)reg);
      Wire.write((uint8_t)value);
    #else
      Wire.send(reg);
      Wire.send(value);
    #endif
    Wire.endTransmission();
  
    /* ToDo: Check for error! */
    return true;
  }
  
  /**************************************************************************/
  /*!
      @brief  Reads an 8 bit value over I2C
  */
  /**************************************************************************/
  byte Adafruit_BNO055::read8(adafruit_bno055_reg_t reg )
  {
    byte value = 0;
  
    Wire.beginTransmission(_address);
    #if ARDUINO >= 100
      Wire.write((uint8_t)reg);
    #else
      Wire.send(reg);
    #endif
    Wire.endTransmission();
    Wire.requestFrom(_address, (byte)1);
    #if ARDUINO >= 100
      value = Wire.read();
    #else
      value = Wire.receive();
    #endif
  
    return value;
  }
  
  /**************************************************************************/
  /*!
      @brief  Reads the specified number of bytes over I2C
  */
  /**************************************************************************/
  bool Adafruit_BNO055::readLen(adafruit_bno055_reg_t reg, byte * buffer, uint8_t len)
  {
    Wire.beginTransmission(_address);
    #if ARDUINO >= 100
      Wire.write((uint8_t)reg);
    #else
      Wire.send(reg);
    #endif
    Wire.endTransmission();
    Wire.requestFrom(_address, (byte)len);
  
    for (uint8_t i = 0; i < len; i++)
    {
      #if ARDUINO >= 100
        buffer[i] = Wire.read();
      #else
        buffer[i] = Wire.receive();
      #endif
    }
  
    /* ToDo: Check for errors! */
    return true;
  }
  