BRIX5

/*!

 * @file Adafruit_BNO055.cpp

 *

 *  @mainpage Adafruit BNO055 Orientation Sensor

 *

 *  @section intro_sec Introduction

 *

 *  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!

 *  ------> https://www.adafruit.com/product/2472

 *

 *  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!

 *

 *  @section author Author

 *

 *  K.Townsend (Adafruit Industries)

 *

 *  @section license License

 *

 *  MIT license, all text above must be included in any redistribution

 */

#if ARDUINO >= 100

#include "Arduino.h"

#else

#include "WProgram.h"

#endif

#include <limits.h>

#include <math.h>

#include "Adafruit_BNO055.h"

/*!

 *  @brief  Instantiates a new Adafruit_BNO055 class

 *  @param  sensorID

 *  @param  address

 */

Adafruit_BNO055::Adafruit_BNO055(int32_t sensorID, uint8_t address) {

  _sensorID = sensorID;

  _address = address;

}

/*!

 *  @brief  Sets up the HW

 *  @param  mode

 *  @return true if process is sucessfull

 */

bool Adafruit_BNO055::begin(adafruit_bno055_opmode_t mode) {

  /* Enable I2C */

  Wire.begin();

  /* BNO055 clock stretches for 500us or more! */

#ifdef ESP8266

  /* Allow for 1000us of clock stretching */

  Wire.setClockStretchLimit(1000);

#endif

  /* Make sure we have the right device */

  uint8_t id = read8(BNO055_CHIP_ID_ADDR);

  if (id != BNO055_ID) {

    /* hold on for boot */

    delay(1000);

    id = read8(BNO055_CHIP_ID_ADDR);

    if (id != BNO055_ID) {

      /* still not? ok bail */

      return false;

    }

  }

  /* 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_SYS_TRIGGER_ADDR, 0x0);

  delay(10);

  /* Set the requested operating mode (see section 3.3) */

  setMode(mode);

  delay(20);

  return true;

}

/*!

 *  @brief  Puts the chip in the specified operating mode

 *  @param  mode

 */

void Adafruit_BNO055::setMode(adafruit_bno055_opmode_t mode) {

  _mode = mode;

  write8(BNO055_OPR_MODE_ADDR, _mode);

  delay(30);

}

/*!

 *  @brief  Changes the chip's axis remap

 *  @param  remapcode

 */

void Adafruit_BNO055::setAxisRemap(

    adafruit_bno055_axis_remap_config_t remapcode) {

  adafruit_bno055_opmode_t modeback = _mode;

  setMode(OPERATION_MODE_CONFIG);

  delay(25);

  write8(BNO055_AXIS_MAP_CONFIG_ADDR, remapcode);

  delay(10);

  /* Set the requested operating mode (see section 3.3) */

  setMode(modeback);

  delay(20);

}

/*!

 *  @brief  Changes the chip's axis signs

 *  @param  remapsign

 */

void Adafruit_BNO055::setAxisSign(adafruit_bno055_axis_remap_sign_t remapsign) {

  adafruit_bno055_opmode_t modeback = _mode;

  setMode(OPERATION_MODE_CONFIG);

  delay(25);

  write8(BNO055_AXIS_MAP_SIGN_ADDR, remapsign);

  delay(10);

  /* Set the requested operating mode (see section 3.3) */

  setMode(modeback);

  delay(20);

}

/*!

 *  @brief  Use the external 32.768KHz crystal

 *  @param  usextal boolean

 */

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

 *   @param  system_status

 *   @param  self_test_result

 *   @param  system_error

 */

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

     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.

 *  @param  sys

 *  @param  gyro

 *  @param  accel

 *  @param  mag

 */

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

 *  @return temperature in degrees celsius

 */

int8_t Adafruit_BNO055::getTemp() {

  int8_t temp = (int8_t)(read8(BNO055_TEMP_ADDR));

  return temp;

}

/*!

 *  @brief   Gets a vector reading from the specified source

 *  @param   vector_type

 *  @return  vector from 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:

    /* 1dps = 16 LSB */

    xyz[0] = ((double)x) / 16.0;

    xyz[1] = ((double)y) / 16.0;

    xyz[2] = ((double)z) / 16.0;

    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

 *  @return quaternion reading

 */

imu::Quaternion Adafruit_BNO055::getQuat() {

  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

 *  @param  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

 *  @param  event

 *  @return always returns true

 */

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

 *  @param  calibData

 *  @return true if read is successful

 */

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

 *  @param  offsets_type

 *  @return true if read is successful

 */

bool Adafruit_BNO055::getSensorOffsets(

    adafruit_bno055_offsets_t &offsets_type) {

  if (isFullyCalibrated()) {

    adafruit_bno055_opmode_t lastMode = _mode;

    setMode(OPERATION_MODE_CONFIG);

    delay(25);

    /* Accel offset range depends on the G-range:

       +/-2g  = +/- 2000 mg

       +/-4g  = +/- 4000 mg

       +/-8g  = +/- 8000 mg

       +/-1§g = +/- 16000 mg */

    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));

    /* Magnetometer offset range = +/- 6400 LSB where 1uT = 16 LSB */

    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));

    /* Gyro offset range depends on the DPS range:

      2000 dps = +/- 32000 LSB

      1000 dps = +/- 16000 LSB

       500 dps = +/- 8000 LSB

       250 dps = +/- 4000 LSB

       125 dps = +/- 2000 LSB

       ... where 1 DPS = 16 LSB */

    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));

    /* Accelerometer radius = +/- 1000 LSB */

    offsets_type.accel_radius =

        (read8(ACCEL_RADIUS_MSB_ADDR) << 8) | (read8(ACCEL_RADIUS_LSB_ADDR));

    /* Magnetometer radius = +/- 960 LSB */

    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

 *  @param  calibData

 */

void Adafruit_BNO055::setSensorOffsets(const uint8_t *calibData) {

  adafruit_bno055_opmode_t lastMode = _mode;

  setMode(OPERATION_MODE_CONFIG);

  delay(25);

  /* Note: Configuration will take place only when user writes to the last

     byte of each config data pair (ex. ACCEL_OFFSET_Z_MSB_ADDR, etc.).

     Therefore the last byte must be written whenever the user wants to

     changes the configuration. */

  /* 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(MAG_OFFSET_X_LSB_ADDR, calibData[6]);

  write8(MAG_OFFSET_X_MSB_ADDR, calibData[7]);

  write8(MAG_OFFSET_Y_LSB_ADDR, calibData[8]);

  write8(MAG_OFFSET_Y_MSB_ADDR, calibData[9]);

  write8(MAG_OFFSET_Z_LSB_ADDR, calibData[10]);

  write8(MAG_OFFSET_Z_MSB_ADDR, calibData[11]);

  write8(GYRO_OFFSET_X_LSB_ADDR, calibData[12]);

  write8(GYRO_OFFSET_X_MSB_ADDR, calibData[13]);

  write8(GYRO_OFFSET_Y_LSB_ADDR, calibData[14]);

  write8(GYRO_OFFSET_Y_MSB_ADDR, calibData[15]);

  write8(GYRO_OFFSET_Z_LSB_ADDR, calibData[16]);

  write8(GYRO_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

 *  @param  offsets_type

 */

void Adafruit_BNO055::setSensorOffsets(

    const adafruit_bno055_offsets_t &offsets_type) {

  adafruit_bno055_opmode_t lastMode = _mode;

  setMode(OPERATION_MODE_CONFIG);

  delay(25);

  /* Note: Configuration will take place only when user writes to the last

     byte of each config data pair (ex. ACCEL_OFFSET_Z_MSB_ADDR, etc.).

     Therefore the last byte must be written whenever the user wants to

     changes the configuration. */

  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(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(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(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);

}

/*!

 *  @brief  Checks of all cal status values are set to 3 (fully calibrated)

 *  @return status of calibration

 */

bool Adafruit_BNO055::isFullyCalibrated() {

  uint8_t system, gyro, accel, mag;

  getCalibration(&system, &gyro, &accel, &mag);

  if (system < 3 || gyro < 3 || accel < 3 || mag < 3)

    return false;

  return true;

}

/*!

 *  @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;

}