File content as of revision 0:39935bb3c1a1:

#ifndef MPU9150_H
#define MPU9150_H
 
#include "mbed.h"
 
// Define registers per MPU6050, Register Map and Descriptions, Rev 4.2, 08/19/2013 6 DOF Motion sensor fusion device
// Invensense Inc., www.invensense.com
// See also MPU-9150 Register Map and Descriptions, Revision 4.0, RM-MPU-9150A-00, 9/12/2012 for registers not listed in 
// above document; the MPU6050 and MPU 9150 are virtually identical but the latter has an on-board magnetic sensor
//
//Magnetometer Registers
#define WHO_AM_I_AK8975A 0x00 // should return 0x48
#define INFO             0x01
#define AK8975A_ST1      0x02  // data ready status bit 0
#define AK8975A_ADDRESS  0x0C<<1
#define AK8975A_XOUT_L   0x03  // data
#define AK8975A_XOUT_H   0x04
#define AK8975A_YOUT_L   0x05
#define AK8975A_YOUT_H   0x06
#define AK8975A_ZOUT_L   0x07
#define AK8975A_ZOUT_H   0x08
#define AK8975A_ST2      0x09  // Data overflow bit 3 and data read error status bit 2
#define AK8975A_CNTL     0x0A  // Power down (0000), single-measurement (0001), self-test (1000) and Fuse ROM (1111) modes on bits 3:0
#define AK8975A_ASTC     0x0C  // Self test control
#define AK8975A_ASAX     0x10  // Fuse ROM x-axis sensitivity adjustment value
#define AK8975A_ASAY     0x11  // Fuse ROM y-axis sensitivity adjustment value
#define AK8975A_ASAZ     0x12  // Fuse ROM z-axis sensitivity adjustment value

#define XGOFFS_TC        0x00 // Bit 7 PWR_MODE, bits 6:1 XG_OFFS_TC, bit 0 OTP_BNK_VLD                 
#define YGOFFS_TC        0x01                                                                          
#define ZGOFFS_TC        0x02
#define X_FINE_GAIN      0x03 // [7:0] fine gain
#define Y_FINE_GAIN      0x04
#define Z_FINE_GAIN      0x05
#define XA_OFFSET_H      0x06 // User-defined trim values for accelerometer
#define XA_OFFSET_L_TC   0x07
#define YA_OFFSET_H      0x08
#define YA_OFFSET_L_TC   0x09
#define ZA_OFFSET_H      0x0A
#define ZA_OFFSET_L_TC   0x0B
#define SELF_TEST_X      0x0D
#define SELF_TEST_Y      0x0E    
#define SELF_TEST_Z      0x0F
#define SELF_TEST_A      0x10
#define XG_OFFS_USRH     0x13  // User-defined trim values for gyroscope, populate with calibration routine
#define XG_OFFS_USRL     0x14
#define YG_OFFS_USRH     0x15
#define YG_OFFS_USRL     0x16
#define ZG_OFFS_USRH     0x17
#define ZG_OFFS_USRL     0x18
#define SMPLRT_DIV       0x19
#define CONFIG           0x1A
#define GYRO_CONFIG      0x1B
#define ACCEL_CONFIG     0x1C
#define FF_THR           0x1D  // Free-fall
#define FF_DUR           0x1E  // Free-fall
#define MOT_THR          0x1F  // Motion detection threshold bits [7:0]
#define MOT_DUR          0x20  // Duration counter threshold for motion interrupt generation, 1 kHz rate, LSB = 1 ms
#define ZMOT_THR         0x21  // Zero-motion detection threshold bits [7:0]
#define ZRMOT_DUR        0x22  // Duration counter threshold for zero motion interrupt generation, 16 Hz rate, LSB = 64 ms
#define FIFO_EN          0x23
#define I2C_MST_CTRL     0x24   
#define I2C_SLV0_ADDR    0x25
#define I2C_SLV0_REG     0x26
#define I2C_SLV0_CTRL    0x27
#define I2C_SLV1_ADDR    0x28
#define I2C_SLV1_REG     0x29
#define I2C_SLV1_CTRL    0x2A
#define I2C_SLV2_ADDR    0x2B
#define I2C_SLV2_REG     0x2C
#define I2C_SLV2_CTRL    0x2D
#define I2C_SLV3_ADDR    0x2E
#define I2C_SLV3_REG     0x2F
#define I2C_SLV3_CTRL    0x30
#define I2C_SLV4_ADDR    0x31
#define I2C_SLV4_REG     0x32
#define I2C_SLV4_DO      0x33
#define I2C_SLV4_CTRL    0x34
#define I2C_SLV4_DI      0x35
#define I2C_MST_STATUS   0x36
#define INT_PIN_CFG      0x37
#define INT_ENABLE       0x38
#define DMP_INT_STATUS   0x39  // Check DMP interrupt
#define INT_STATUS       0x3A
#define ACCEL_XOUT_H     0x3B
#define ACCEL_XOUT_L     0x3C
#define ACCEL_YOUT_H     0x3D
#define ACCEL_YOUT_L     0x3E
#define ACCEL_ZOUT_H     0x3F
#define ACCEL_ZOUT_L     0x40
#define TEMP_OUT_H       0x41
#define TEMP_OUT_L       0x42
#define GYRO_XOUT_H      0x43
#define GYRO_XOUT_L      0x44
#define GYRO_YOUT_H      0x45
#define GYRO_YOUT_L      0x46
#define GYRO_ZOUT_H      0x47
#define GYRO_ZOUT_L      0x48
#define EXT_SENS_DATA_00 0x49
#define EXT_SENS_DATA_01 0x4A
#define EXT_SENS_DATA_02 0x4B
#define EXT_SENS_DATA_03 0x4C
#define EXT_SENS_DATA_04 0x4D
#define EXT_SENS_DATA_05 0x4E
#define EXT_SENS_DATA_06 0x4F
#define EXT_SENS_DATA_07 0x50
#define EXT_SENS_DATA_08 0x51
#define EXT_SENS_DATA_09 0x52
#define EXT_SENS_DATA_10 0x53
#define EXT_SENS_DATA_11 0x54
#define EXT_SENS_DATA_12 0x55
#define EXT_SENS_DATA_13 0x56
#define EXT_SENS_DATA_14 0x57
#define EXT_SENS_DATA_15 0x58
#define EXT_SENS_DATA_16 0x59
#define EXT_SENS_DATA_17 0x5A
#define EXT_SENS_DATA_18 0x5B
#define EXT_SENS_DATA_19 0x5C
#define EXT_SENS_DATA_20 0x5D
#define EXT_SENS_DATA_21 0x5E
#define EXT_SENS_DATA_22 0x5F
#define EXT_SENS_DATA_23 0x60
#define MOT_DETECT_STATUS 0x61
#define I2C_SLV0_DO      0x63
#define I2C_SLV1_DO      0x64
#define I2C_SLV2_DO      0x65
#define I2C_SLV3_DO      0x66
#define I2C_MST_DELAY_CTRL 0x67
#define SIGNAL_PATH_RESET  0x68
#define MOT_DETECT_CTRL   0x69
#define USER_CTRL        0x6A  // Bit 7 enable DMP, bit 3 reset DMP
#define PWR_MGMT_1       0x6B // Device defaults to the SLEEP mode
#define PWR_MGMT_2       0x6C
#define DMP_BANK         0x6D  // Activates a specific bank in the DMP
#define DMP_RW_PNT       0x6E  // Set read/write pointer to a specific start address in specified DMP bank
#define DMP_REG          0x6F  // Register in DMP from which to read or to which to write
#define DMP_REG_1        0x70
#define DMP_REG_2        0x71
#define FIFO_COUNTH      0x72
#define FIFO_COUNTL      0x73
#define FIFO_R_W         0x74
#define WHO_AM_I_MPU9150 0x75 // Should return 0x68


// Using the GY-9150 breakout board, ADO is set to 0 
// Seven-bit device address is 110100 for ADO = 0 and 110101 for ADO = 1
// mbed uses the eight-bit device address, so shift seven-bit addresses left by one!
#define ADO 0
#if ADO
#define MPU9150_ADDRESS 0x69<<1  // Device address when ADO = 1
#else
#define MPU9150_ADDRESS 0x68<<1  // Device address when ADO = 0
#endif  

// Set initial input parameters
enum Ascale {
  AFS_2G = 0,
  AFS_4G,
  AFS_8G,
  AFS_16G
};

enum Gscale {
  GFS_250DPS = 0,
  GFS_500DPS,
  GFS_1000DPS,
  GFS_2000DPS
};

uint8_t Ascale = AFS_2G;     // AFS_2G, AFS_4G, AFS_8G, AFS_16G
uint8_t Gscale = GFS_250DPS; // GFS_250DPS, GFS_500DPS, GFS_1000DPS, GFS_2000DPS
float aRes, gRes, mRes;      // scale resolutions per LSB for the sensors

//Set up I2C, (SDA,SCL)
I2C i2c(I2C_SDA, I2C_SCL);

DigitalOut myled(LED1);
    
// Pin definitions
int intPin = 12;  // These can be changed, 2 and 3 are the Arduinos ext int pins

int16_t accelCount[3];  // Stores the 16-bit signed accelerometer sensor output
int16_t gyroCount[3];   // Stores the 16-bit signed gyro sensor output
int16_t magCount[3];    // Stores the 16-bit signed magnetometer sensor output
float magCalibration[3] = {0, 0, 0}, magbias[3] = {0, 0, 0};  // Factory mag calibration and mag bias
float gyroBias[3] = {0, 0, 0}, accelBias[3] = {0, 0, 0}; // Bias corrections for gyro and accelerometer
float ax, ay, az, gx, gy, gz, mx, my, mz; // variables to hold latest sensor data values 
int16_t tempCount;   // Stores the real internal chip temperature in degrees Celsius
float temperature;
float SelfTest[6];

int delt_t = 0; // used to control display output rate
int count = 0;  // used to control display output rate

// parameters for 6 DoF sensor fusion calculations
float PI = 3.14159265358979323846f;
float GyroMeasError = PI * (60.0f / 180.0f);     // gyroscope measurement error in rads/s (start at 60 deg/s), then reduce after ~10 s to 3
float beta = sqrt(3.0f / 4.0f) * GyroMeasError;  // compute beta
float GyroMeasDrift = PI * (1.0f / 180.0f);      // gyroscope measurement drift in rad/s/s (start at 0.0 deg/s/s)
float zeta = sqrt(3.0f / 4.0f) * GyroMeasDrift;  // compute zeta, the other free parameter in the Madgwick scheme usually set to a small or zero value
#define Kp 2.0f * 5.0f // these are the free parameters in the Mahony filter and fusion scheme, Kp for proportional feedback, Ki for integral
#define Ki 0.0f

float pitch, yaw, roll;
float deltat = 0.0f;                             // integration interval for both filter schemes
int lastUpdate = 0, firstUpdate = 0, Now = 0;    // used to calculate integration interval                               // used to calculate integration interval
float q[4] = {1.0f, 0.0f, 0.0f, 0.0f};           // vector to hold quaternion
float eInt[3] = {0.0f, 0.0f, 0.0f};              // vector to hold integral error for Mahony method

class MPU9150 {
 
    protected:
 
    public:
  //===================================================================================================================
//====== Set of useful function to access acceleratio, gyroscope, and temperature data
//===================================================================================================================

    void writeByte(uint8_t address, uint8_t subAddress, uint8_t data)
{
   char data_write[2];
   data_write[0] = subAddress;
   data_write[1] = data;
   i2c.write(address, data_write, 2, 0);
}

    char readByte(uint8_t address, uint8_t subAddress)
{
    char data[1]; // `data` will store the register data     
    char data_write[1];
    data_write[0] = subAddress;
    i2c.write(address, data_write, 1, 1); // no stop
    i2c.read(address, data, 1, 0); 
    return data[0]; 
}

    void readBytes(uint8_t address, uint8_t subAddress, uint8_t count, uint8_t * dest)
{     
    char data[14];
    char data_write[1];
    data_write[0] = subAddress;
    i2c.write(address, data_write, 1, 1); // no stop
    i2c.read(address, data, count, 0); 
    for(int ii = 0; ii < count; ii++) {
     dest[ii] = data[ii];
    }
} 
 

void getGres() {
  switch (Gscale)
  {
    // Possible gyro scales (and their register bit settings) are:
    // 250 DPS (00), 500 DPS (01), 1000 DPS (10), and 2000 DPS  (11). 
        // Here's a bit of an algorith to calculate DPS/(ADC tick) based on that 2-bit value:
    case GFS_250DPS:
          gRes = 250.0/32768.0;
          break;
    case GFS_500DPS:
          gRes = 500.0/32768.0;
          break;
    case GFS_1000DPS:
          gRes = 1000.0/32768.0;
          break;
    case GFS_2000DPS:
          gRes = 2000.0/32768.0;
          break;
  }
}


void getAres() {
  switch (Ascale)
  {
    // Possible accelerometer scales (and their register bit settings) are:
    // 2 Gs (00), 4 Gs (01), 8 Gs (10), and 16 Gs  (11). 
        // Here's a bit of an algorith to calculate DPS/(ADC tick) based on that 2-bit value:
    case AFS_2G:
          aRes = 2.0/32768.0;
          break;
    case AFS_4G:
          aRes = 4.0/32768.0;
          break;
    case AFS_8G:
          aRes = 8.0/32768.0;
          break;
    case AFS_16G:
          aRes = 16.0/32768.0;
          break;
  }
}


void readAccelData(int16_t * destination)
{
  uint8_t rawData[6];  // x/y/z accel register data stored here
  readBytes(MPU9150_ADDRESS, ACCEL_XOUT_H, 6, &rawData[0]);  // Read the six raw data registers into data array
  destination[0] = (int16_t)(((int16_t)rawData[0] << 8) | rawData[1]) ;  // Turn the MSB and LSB into a signed 16-bit value
  destination[1] = (int16_t)(((int16_t)rawData[2] << 8) | rawData[3]) ;  
  destination[2] = (int16_t)(((int16_t)rawData[4] << 8) | rawData[5]) ; 
}

void readGyroData(int16_t * destination)
{
  uint8_t rawData[6];  // x/y/z gyro register data stored here
  readBytes(MPU9150_ADDRESS, GYRO_XOUT_H, 6, &rawData[0]);  // Read the six raw data registers sequentially into data array
  destination[0] = (int16_t)(((int16_t)rawData[0] << 8) | rawData[1]) ;  // Turn the MSB and LSB into a signed 16-bit value
  destination[1] = (int16_t)(((int16_t)rawData[2] << 8) | rawData[3]) ;  
  destination[2] = (int16_t)(((int16_t)rawData[4] << 8) | rawData[5]) ; 
}

void readMagData(int16_t * destination)
{
  uint8_t rawData[6];  // x/y/z gyro register data stored here
  writeByte(AK8975A_ADDRESS, AK8975A_CNTL, 0x01); // toggle enable data read from magnetometer, no continuous read mode!
  wait(0.01);
  // Only accept a new magnetometer data read if the data ready bit is set and 
  // if there are no sensor overflow or data read errors
  if(readByte(AK8975A_ADDRESS, AK8975A_ST1) & 0x01) { // wait for magnetometer data ready bit to be set
  readBytes(AK8975A_ADDRESS, AK8975A_XOUT_L, 6, &rawData[0]);  // Read the six raw data registers sequentially into data array
  destination[0] = ((int16_t)rawData[1] << 8) | rawData[0] ;  // Turn the MSB and LSB into a signed 16-bit value
  destination[1] = ((int16_t)rawData[3] << 8) | rawData[2] ;  
  destination[2] = ((int16_t)rawData[5] << 8) | rawData[4] ; 
  }
}

void initAK8975A(float * destination)
{
  uint8_t rawData[3];  // x/y/z gyro register data stored here
  writeByte(AK8975A_ADDRESS, AK8975A_CNTL, 0x00); // Power down
  wait(0.01);
  writeByte(AK8975A_ADDRESS, AK8975A_CNTL, 0x0F); // Enter Fuse ROM access mode
  wait(0.01);
  readBytes(AK8975A_ADDRESS, AK8975A_ASAX, 3, &rawData[0]);  // Read the x-, y-, and z-axis calibration values
  destination[0] =  (float)(rawData[0] - 128)/256.0f + 1.0f; // Return x-axis sensitivity adjustment values
  destination[1] =  (float)(rawData[1] - 128)/256.0f + 1.0f;  
  destination[2] =  (float)(rawData[2] - 128)/256.0f + 1.0f; 
}

int16_t readTempData()
{
  uint8_t rawData[2];  // x/y/z gyro register data stored here
  readBytes(MPU9150_ADDRESS, TEMP_OUT_H, 2, &rawData[0]);  // Read the two raw data registers sequentially into data array 
  return ((int16_t)rawData[0] << 8) | rawData[1] ;  // Turn the MSB and LSB into a 16-bit value
}

void resetMPU9150() {
  // reset device
  writeByte(MPU9150_ADDRESS, PWR_MGMT_1, 0x80); // Write a one to bit 7 reset bit; toggle reset device
  wait(0.1);
  }
  


void initMPU9150()
{  
 // Initialize MPU9150 device
 // wake up device
  writeByte(MPU9150_ADDRESS, PWR_MGMT_1, 0x00); // Clear sleep mode bit (6), enable all sensors 
  wait(0.1); // Delay 100 ms for PLL to get established on x-axis gyro; should check for PLL ready interrupt  

 // get stable time source
  writeByte(MPU9150_ADDRESS, PWR_MGMT_1, 0x01);  // Set clock source to be PLL with x-axis gyroscope reference, bits 2:0 = 001

 // Configure Gyro and Accelerometer
 // Disable FSYNC and set accelerometer and gyro bandwidth to 44 and 42 Hz, respectively; 
 // DLPF_CFG = bits 2:0 = 010; this sets the sample rate at 1 kHz for both
 // Maximum delay is 4.9 ms which is just over a 200 Hz maximum rate
  writeByte(MPU9150_ADDRESS, CONFIG, 0x03);  
 
 // Set sample rate = gyroscope output rate/(1 + SMPLRT_DIV)
  writeByte(MPU9150_ADDRESS, SMPLRT_DIV, 0x04);  // Use a 200 Hz rate; the same rate set in CONFIG above
 
 // Set gyroscope full scale range
 // Range selects FS_SEL and AFS_SEL are 0 - 3, so 2-bit values are left-shifted into positions 4:3
  uint8_t c =  readByte(MPU9150_ADDRESS, GYRO_CONFIG);
  writeByte(MPU9150_ADDRESS, GYRO_CONFIG, c & ~0xE0); // Clear self-test bits [7:5] 
  writeByte(MPU9150_ADDRESS, GYRO_CONFIG, c & ~0x18); // Clear AFS bits [4:3]
  writeByte(MPU9150_ADDRESS, GYRO_CONFIG, c | Gscale << 3); // Set full scale range for the gyro
   
 // Set accelerometer configuration
  c =  readByte(MPU9150_ADDRESS, ACCEL_CONFIG);
  writeByte(MPU9150_ADDRESS, ACCEL_CONFIG, c & ~0xE0); // Clear self-test bits [7:5] 
  writeByte(MPU9150_ADDRESS, ACCEL_CONFIG, c & ~0x18); // Clear AFS bits [4:3]
  writeByte(MPU9150_ADDRESS, ACCEL_CONFIG, c | Ascale << 3); // Set full scale range for the accelerometer 

 // The accelerometer, gyro, and thermometer are set to 1 kHz sample rates, 
 // but all these rates are further reduced by a factor of 5 to 200 Hz because of the SMPLRT_DIV setting

  // Configure Interrupts and Bypass Enable
  // Set interrupt pin active high, push-pull, and clear on read of INT_STATUS, enable I2C_BYPASS_EN so additional chips 
  // can join the I2C bus and all can be controlled by the Arduino as master
   writeByte(MPU9150_ADDRESS, INT_PIN_CFG, 0x22);    
   writeByte(MPU9150_ADDRESS, INT_ENABLE, 0x01);  // Enable data ready (bit 0) interrupt
}

// Function which accumulates gyro and accelerometer data after device initialization. It calculates the average
// of the at-rest readings and then loads the resulting offsets into accelerometer and gyro bias registers.
void calibrateMPU9150(float * dest1, float * dest2)
{  
  uint8_t data[12]; // data array to hold accelerometer and gyro x, y, z, data
  uint16_t ii, packet_count, fifo_count;
  int32_t gyro_bias[3] = {0, 0, 0}, accel_bias[3] = {0, 0, 0};
  
// reset device, reset all registers, clear gyro and accelerometer bias registers
  writeByte(MPU9150_ADDRESS, PWR_MGMT_1, 0x80); // Write a one to bit 7 reset bit; toggle reset device
  wait(0.1);  
   
// get stable time source
// Set clock source to be PLL with x-axis gyroscope reference, bits 2:0 = 001
  writeByte(MPU9150_ADDRESS, PWR_MGMT_1, 0x01);  
  writeByte(MPU9150_ADDRESS, PWR_MGMT_2, 0x00); 
  wait(0.2);
  
// Configure device for bias calculation
  writeByte(MPU9150_ADDRESS, INT_ENABLE, 0x00);   // Disable all interrupts
  writeByte(MPU9150_ADDRESS, FIFO_EN, 0x00);      // Disable FIFO
  writeByte(MPU9150_ADDRESS, PWR_MGMT_1, 0x00);   // Turn on internal clock source
  writeByte(MPU9150_ADDRESS, I2C_MST_CTRL, 0x00); // Disable I2C master
  writeByte(MPU9150_ADDRESS, USER_CTRL, 0x00);    // Disable FIFO and I2C master modes
  writeByte(MPU9150_ADDRESS, USER_CTRL, 0x0C);    // Reset FIFO and DMP
  wait(0.015);
  
// Configure MPU9150 gyro and accelerometer for bias calculation
  writeByte(MPU9150_ADDRESS, CONFIG, 0x01);      // Set low-pass filter to 188 Hz
  writeByte(MPU9150_ADDRESS, SMPLRT_DIV, 0x00);  // Set sample rate to 1 kHz
  writeByte(MPU9150_ADDRESS, GYRO_CONFIG, 0x00);  // Set gyro full-scale to 250 degrees per second, maximum sensitivity
  writeByte(MPU9150_ADDRESS, ACCEL_CONFIG, 0x00); // Set accelerometer full-scale to 2 g, maximum sensitivity
 
  uint16_t  gyrosensitivity  = 131;   // = 131 LSB/degrees/sec
  uint16_t  accelsensitivity = 16384;  // = 16384 LSB/g

// Configure FIFO to capture accelerometer and gyro data for bias calculation
  writeByte(MPU9150_ADDRESS, USER_CTRL, 0x40);   // Enable FIFO  
  writeByte(MPU9150_ADDRESS, FIFO_EN, 0x78);     // Enable gyro and accelerometer sensors for FIFO (max size 1024 bytes in MPU9150)
  wait(0.08); // accumulate 80 samples in 80 milliseconds = 960 bytes

// At end of sample accumulation, turn off FIFO sensor read
  writeByte(MPU9150_ADDRESS, FIFO_EN, 0x00);        // Disable gyro and accelerometer sensors for FIFO
  readBytes(MPU9150_ADDRESS, FIFO_COUNTH, 2, &data[0]); // read FIFO sample count
  fifo_count = ((uint16_t)data[0] << 8) | data[1];
  packet_count = fifo_count/12;// How many sets of full gyro and accelerometer data for averaging

  for (ii = 0; ii < packet_count; ii++) {
    int16_t accel_temp[3] = {0, 0, 0}, gyro_temp[3] = {0, 0, 0};
    readBytes(MPU9150_ADDRESS, FIFO_R_W, 12, &data[0]); // read data for averaging
    accel_temp[0] = (int16_t) (((int16_t)data[0] << 8) | data[1]  ) ;  // Form signed 16-bit integer for each sample in FIFO
    accel_temp[1] = (int16_t) (((int16_t)data[2] << 8) | data[3]  ) ;
    accel_temp[2] = (int16_t) (((int16_t)data[4] << 8) | data[5]  ) ;    
    gyro_temp[0]  = (int16_t) (((int16_t)data[6] << 8) | data[7]  ) ;
    gyro_temp[1]  = (int16_t) (((int16_t)data[8] << 8) | data[9]  ) ;
    gyro_temp[2]  = (int16_t) (((int16_t)data[10] << 8) | data[11]) ;
    
    accel_bias[0] += (int32_t) accel_temp[0]; // Sum individual signed 16-bit biases to get accumulated signed 32-bit biases
    accel_bias[1] += (int32_t) accel_temp[1];
    accel_bias[2] += (int32_t) accel_temp[2];
    gyro_bias[0]  += (int32_t) gyro_temp[0];
    gyro_bias[1]  += (int32_t) gyro_temp[1];
    gyro_bias[2]  += (int32_t) gyro_temp[2];
            
}
    accel_bias[0] /= (int32_t) packet_count; // Normalize sums to get average count biases
    accel_bias[1] /= (int32_t) packet_count;
    accel_bias[2] /= (int32_t) packet_count;
    gyro_bias[0]  /= (int32_t) packet_count;
    gyro_bias[1]  /= (int32_t) packet_count;
    gyro_bias[2]  /= (int32_t) packet_count;
    
  if(accel_bias[2] > 0L) {accel_bias[2] -= (int32_t) accelsensitivity;}  // Remove gravity from the z-axis accelerometer bias calculation
  else {accel_bias[2] += (int32_t) accelsensitivity;}
 
// Construct the gyro biases for push to the hardware gyro bias registers, which are reset to zero upon device startup
  data[0] = (-gyro_bias[0]/4  >> 8) & 0xFF; // Divide by 4 to get 32.9 LSB per deg/s to conform to expected bias input format
  data[1] = (-gyro_bias[0]/4)       & 0xFF; // Biases are additive, so change sign on calculated average gyro biases
  data[2] = (-gyro_bias[1]/4  >> 8) & 0xFF;
  data[3] = (-gyro_bias[1]/4)       & 0xFF;
  data[4] = (-gyro_bias[2]/4  >> 8) & 0xFF;
  data[5] = (-gyro_bias[2]/4)       & 0xFF;

/// Push gyro biases to hardware registers
  writeByte(MPU9150_ADDRESS, XG_OFFS_USRH, data[0]); 
  writeByte(MPU9150_ADDRESS, XG_OFFS_USRL, data[1]);
  writeByte(MPU9150_ADDRESS, YG_OFFS_USRH, data[2]);
  writeByte(MPU9150_ADDRESS, YG_OFFS_USRL, data[3]);
  writeByte(MPU9150_ADDRESS, ZG_OFFS_USRH, data[4]);
  writeByte(MPU9150_ADDRESS, ZG_OFFS_USRL, data[5]);

  dest1[0] = (float) gyro_bias[0]/(float) gyrosensitivity; // construct gyro bias in deg/s for later manual subtraction
  dest1[1] = (float) gyro_bias[1]/(float) gyrosensitivity;
  dest1[2] = (float) gyro_bias[2]/(float) gyrosensitivity;

// Construct the accelerometer biases for push to the hardware accelerometer bias registers. These registers contain
// factory trim values which must be added to the calculated accelerometer biases; on boot up these registers will hold
// non-zero values. In addition, bit 0 of the lower byte must be preserved since it is used for temperature
// compensation calculations. Accelerometer bias registers expect bias input as 2048 LSB per g, so that
// the accelerometer biases calculated above must be divided by 8.

  int32_t accel_bias_reg[3] = {0, 0, 0}; // A place to hold the factory accelerometer trim biases
  readBytes(MPU9150_ADDRESS, XA_OFFSET_H, 2, &data[0]); // Read factory accelerometer trim values
  accel_bias_reg[0] = (int16_t) ((int16_t)data[0] << 8) | data[1];
  readBytes(MPU9150_ADDRESS, YA_OFFSET_H, 2, &data[0]);
  accel_bias_reg[1] = (int16_t) ((int16_t)data[0] << 8) | data[1];
  readBytes(MPU9150_ADDRESS, ZA_OFFSET_H, 2, &data[0]);
  accel_bias_reg[2] = (int16_t) ((int16_t)data[0] << 8) | data[1];
  
  uint32_t mask = 1uL; // Define mask for temperature compensation bit 0 of lower byte of accelerometer bias registers
  uint8_t mask_bit[3] = {0, 0, 0}; // Define array to hold mask bit for each accelerometer bias axis
  
  for(ii = 0; ii < 3; ii++) {
    if(accel_bias_reg[ii] & mask) mask_bit[ii] = 0x01; // If temperature compensation bit is set, record that fact in mask_bit
  }

  // Construct total accelerometer bias, including calculated average accelerometer bias from above
  accel_bias_reg[0] -= (accel_bias[0]/8); // Subtract calculated averaged accelerometer bias scaled to 2048 LSB/g (16 g full scale)
  accel_bias_reg[1] -= (accel_bias[1]/8);
  accel_bias_reg[2] -= (accel_bias[2]/8);
 
  data[0] = (accel_bias_reg[0] >> 8) & 0xFF;
  data[1] = (accel_bias_reg[0])      & 0xFF;
  data[1] = data[1] | mask_bit[0]; // preserve temperature compensation bit when writing back to accelerometer bias registers
  data[2] = (accel_bias_reg[1] >> 8) & 0xFF;
  data[3] = (accel_bias_reg[1])      & 0xFF;
  data[3] = data[3] | mask_bit[1]; // preserve temperature compensation bit when writing back to accelerometer bias registers
  data[4] = (accel_bias_reg[2] >> 8) & 0xFF;
  data[5] = (accel_bias_reg[2])      & 0xFF;
  data[5] = data[5] | mask_bit[2]; // preserve temperature compensation bit when writing back to accelerometer bias registers

// Apparently this is not working for the acceleration biases in the MPU-9250
// Are we handling the temperature correction bit properly?
// Push accelerometer biases to hardware registers
  writeByte(MPU9150_ADDRESS, XA_OFFSET_H, data[0]);  
  writeByte(MPU9150_ADDRESS, XA_OFFSET_L_TC, data[1]);
  writeByte(MPU9150_ADDRESS, YA_OFFSET_H, data[2]);
  writeByte(MPU9150_ADDRESS, YA_OFFSET_L_TC, data[3]);
  writeByte(MPU9150_ADDRESS, ZA_OFFSET_H, data[4]);
  writeByte(MPU9150_ADDRESS, ZA_OFFSET_L_TC, data[5]);

// Output scaled accelerometer biases for manual subtraction in the main program
   dest2[0] = (float)accel_bias[0]/(float)accelsensitivity; 
   dest2[1] = (float)accel_bias[1]/(float)accelsensitivity;
   dest2[2] = (float)accel_bias[2]/(float)accelsensitivity;
}


// Accelerometer and gyroscope self test; check calibration wrt factory settings
void MPU9150SelfTest(float * destination) // Should return percent deviation from factory trim values, +/- 14 or less deviation is a pass
{
   uint8_t rawData[4] = {0, 0, 0, 0};
   uint8_t selfTest[6];
   float factoryTrim[6];
   
   // Configure the accelerometer for self-test
   writeByte(MPU9150_ADDRESS, ACCEL_CONFIG, 0xF0); // Enable self test on all three axes and set accelerometer range to +/- 8 g
   writeByte(MPU9150_ADDRESS, GYRO_CONFIG,  0xE0); // Enable self test on all three axes and set gyro range to +/- 250 degrees/s
   wait(0.25);  // Delay a while to let the device execute the self-test
   rawData[0] = readByte(MPU9150_ADDRESS, SELF_TEST_X); // X-axis self-test results
   rawData[1] = readByte(MPU9150_ADDRESS, SELF_TEST_Y); // Y-axis self-test results
   rawData[2] = readByte(MPU9150_ADDRESS, SELF_TEST_Z); // Z-axis self-test results
   rawData[3] = readByte(MPU9150_ADDRESS, SELF_TEST_A); // Mixed-axis self-test results
   // Extract the acceleration test results first
   selfTest[0] = (rawData[0] >> 3) | (rawData[3] & 0x30) >> 4 ; // XA_TEST result is a five-bit unsigned integer
   selfTest[1] = (rawData[1] >> 3) | (rawData[3] & 0x0C) >> 4 ; // YA_TEST result is a five-bit unsigned integer
   selfTest[2] = (rawData[2] >> 3) | (rawData[3] & 0x03) >> 4 ; // ZA_TEST result is a five-bit unsigned integer
   // Extract the gyration test results first
   selfTest[3] = rawData[0]  & 0x1F ; // XG_TEST result is a five-bit unsigned integer
   selfTest[4] = rawData[1]  & 0x1F ; // YG_TEST result is a five-bit unsigned integer
   selfTest[5] = rawData[2]  & 0x1F ; // ZG_TEST result is a five-bit unsigned integer   
   // Process results to allow final comparison with factory set values
   factoryTrim[0] = (4096.0f*0.34f)*(pow( (0.92f/0.34f) , ((selfTest[0] - 1.0f)/30.0f))); // FT[Xa] factory trim calculation
   factoryTrim[1] = (4096.0f*0.34f)*(pow( (0.92f/0.34f) , ((selfTest[1] - 1.0f)/30.0f))); // FT[Ya] factory trim calculation
   factoryTrim[2] = (4096.0f*0.34f)*(pow( (0.92f/0.34f) , ((selfTest[2] - 1.0f)/30.0f))); // FT[Za] factory trim calculation
   factoryTrim[3] =  ( 25.0f*131.0f)*(pow( 1.046f , (selfTest[3] - 1.0f) ));             // FT[Xg] factory trim calculation
   factoryTrim[4] =  (-25.0f*131.0f)*(pow( 1.046f , (selfTest[4] - 1.0f) ));             // FT[Yg] factory trim calculation
   factoryTrim[5] =  ( 25.0f*131.0f)*(pow( 1.046f , (selfTest[5] - 1.0f) ));             // FT[Zg] factory trim calculation
   
 //  Output self-test results and factory trim calculation if desired
 //  Serial.println(selfTest[0]); Serial.println(selfTest[1]); Serial.println(selfTest[2]);
 //  Serial.println(selfTest[3]); Serial.println(selfTest[4]); Serial.println(selfTest[5]);
 //  Serial.println(factoryTrim[0]); Serial.println(factoryTrim[1]); Serial.println(factoryTrim[2]);
 //  Serial.println(factoryTrim[3]); Serial.println(factoryTrim[4]); Serial.println(factoryTrim[5]);

 // Report results as a ratio of (STR - FT)/FT; the change from Factory Trim of the Self-Test Response
 // To get to percent, must multiply by 100 and subtract result from 100
   for (int i = 0; i < 6; i++) {
     destination[i] = 100.0f + 100.0f*(selfTest[i] - factoryTrim[i])/factoryTrim[i]; // Report percent differences
   }
   
}



// Implementation of Sebastian Madgwick's "...efficient orientation filter for... inertial/magnetic sensor arrays"
// (see http://www.x-io.co.uk/category/open-source/ for examples and more details)
// which fuses acceleration, rotation rate, and magnetic moments to produce a quaternion-based estimate of absolute
// device orientation -- which can be converted to yaw, pitch, and roll. Useful for stabilizing quadcopters, etc.
// The performance of the orientation filter is at least as good as conventional Kalman-based filtering algorithms
// but is much less computationally intensive---it can be performed on a 3.3 V Pro Mini operating at 8 MHz!
        void MadgwickQuaternionUpdate(float ax, float ay, float az, float gx, float gy, float gz, float mx, float my, float mz)
        {
            float q1 = q[0], q2 = q[1], q3 = q[2], q4 = q[3];   // short name local variable for readability
            float norm;
            float hx, hy, _2bx, _2bz;
            float s1, s2, s3, s4;
            float qDot1, qDot2, qDot3, qDot4;

            // Auxiliary variables to avoid repeated arithmetic
            float _2q1mx;
            float _2q1my;
            float _2q1mz;
            float _2q2mx;
            float _4bx;
            float _4bz;
            float _2q1 = 2.0f * q1;
            float _2q2 = 2.0f * q2;
            float _2q3 = 2.0f * q3;
            float _2q4 = 2.0f * q4;
            float _2q1q3 = 2.0f * q1 * q3;
            float _2q3q4 = 2.0f * q3 * q4;
            float q1q1 = q1 * q1;
            float q1q2 = q1 * q2;
            float q1q3 = q1 * q3;
            float q1q4 = q1 * q4;
            float q2q2 = q2 * q2;
            float q2q3 = q2 * q3;
            float q2q4 = q2 * q4;
            float q3q3 = q3 * q3;
            float q3q4 = q3 * q4;
            float q4q4 = q4 * q4;

            // Normalise accelerometer measurement
            norm = sqrt(ax * ax + ay * ay + az * az);
            if (norm == 0.0f) return; // handle NaN
            norm = 1.0f/norm;
            ax *= norm;
            ay *= norm;
            az *= norm;

            // Normalise magnetometer measurement
            norm = sqrt(mx * mx + my * my + mz * mz);
            if (norm == 0.0f) return; // handle NaN
            norm = 1.0f/norm;
            mx *= norm;
            my *= norm;
            mz *= norm;

            // Reference direction of Earth's magnetic field
            _2q1mx = 2.0f * q1 * mx;
            _2q1my = 2.0f * q1 * my;
            _2q1mz = 2.0f * q1 * mz;
            _2q2mx = 2.0f * q2 * mx;
            hx = mx * q1q1 - _2q1my * q4 + _2q1mz * q3 + mx * q2q2 + _2q2 * my * q3 + _2q2 * mz * q4 - mx * q3q3 - mx * q4q4;
            hy = _2q1mx * q4 + my * q1q1 - _2q1mz * q2 + _2q2mx * q3 - my * q2q2 + my * q3q3 + _2q3 * mz * q4 - my * q4q4;
            _2bx = sqrt(hx * hx + hy * hy);
            _2bz = -_2q1mx * q3 + _2q1my * q2 + mz * q1q1 + _2q2mx * q4 - mz * q2q2 + _2q3 * my * q4 - mz * q3q3 + mz * q4q4;
            _4bx = 2.0f * _2bx;
            _4bz = 2.0f * _2bz;

            // Gradient decent algorithm corrective step
            s1 = -_2q3 * (2.0f * q2q4 - _2q1q3 - ax) + _2q2 * (2.0f * q1q2 + _2q3q4 - ay) - _2bz * q3 * (_2bx * (0.5f - q3q3 - q4q4) + _2bz * (q2q4 - q1q3) - mx) + (-_2bx * q4 + _2bz * q2) * (_2bx * (q2q3 - q1q4) + _2bz * (q1q2 + q3q4) - my) + _2bx * q3 * (_2bx * (q1q3 + q2q4) + _2bz * (0.5f - q2q2 - q3q3) - mz);
            s2 = _2q4 * (2.0f * q2q4 - _2q1q3 - ax) + _2q1 * (2.0f * q1q2 + _2q3q4 - ay) - 4.0f * q2 * (1.0f - 2.0f * q2q2 - 2.0f * q3q3 - az) + _2bz * q4 * (_2bx * (0.5f - q3q3 - q4q4) + _2bz * (q2q4 - q1q3) - mx) + (_2bx * q3 + _2bz * q1) * (_2bx * (q2q3 - q1q4) + _2bz * (q1q2 + q3q4) - my) + (_2bx * q4 - _4bz * q2) * (_2bx * (q1q3 + q2q4) + _2bz * (0.5f - q2q2 - q3q3) - mz);
            s3 = -_2q1 * (2.0f * q2q4 - _2q1q3 - ax) + _2q4 * (2.0f * q1q2 + _2q3q4 - ay) - 4.0f * q3 * (1.0f - 2.0f * q2q2 - 2.0f * q3q3 - az) + (-_4bx * q3 - _2bz * q1) * (_2bx * (0.5f - q3q3 - q4q4) + _2bz * (q2q4 - q1q3) - mx) + (_2bx * q2 + _2bz * q4) * (_2bx * (q2q3 - q1q4) + _2bz * (q1q2 + q3q4) - my) + (_2bx * q1 - _4bz * q3) * (_2bx * (q1q3 + q2q4) + _2bz * (0.5f - q2q2 - q3q3) - mz);
            s4 = _2q2 * (2.0f * q2q4 - _2q1q3 - ax) + _2q3 * (2.0f * q1q2 + _2q3q4 - ay) + (-_4bx * q4 + _2bz * q2) * (_2bx * (0.5f - q3q3 - q4q4) + _2bz * (q2q4 - q1q3) - mx) + (-_2bx * q1 + _2bz * q3) * (_2bx * (q2q3 - q1q4) + _2bz * (q1q2 + q3q4) - my) + _2bx * q2 * (_2bx * (q1q3 + q2q4) + _2bz * (0.5f - q2q2 - q3q3) - mz);
            norm = sqrt(s1 * s1 + s2 * s2 + s3 * s3 + s4 * s4);    // normalise step magnitude
            norm = 1.0f/norm;
            s1 *= norm;
            s2 *= norm;
            s3 *= norm;
            s4 *= norm;

            // Compute rate of change of quaternion
            qDot1 = 0.5f * (-q2 * gx - q3 * gy - q4 * gz) - beta * s1;
            qDot2 = 0.5f * (q1 * gx + q3 * gz - q4 * gy) - beta * s2;
            qDot3 = 0.5f * (q1 * gy - q2 * gz + q4 * gx) - beta * s3;
            qDot4 = 0.5f * (q1 * gz + q2 * gy - q3 * gx) - beta * s4;

            // Integrate to yield quaternion
            q1 += qDot1 * deltat;
            q2 += qDot2 * deltat;
            q3 += qDot3 * deltat;
            q4 += qDot4 * deltat;
            norm = sqrt(q1 * q1 + q2 * q2 + q3 * q3 + q4 * q4);    // normalise quaternion
            norm = 1.0f/norm;
            q[0] = q1 * norm;
            q[1] = q2 * norm;
            q[2] = q3 * norm;
            q[3] = q4 * norm;

        }
  
  
  
 // Similar to Madgwick scheme but uses proportional and integral filtering on the error between estimated reference vectors and
 // measured ones. 
            void MahonyQuaternionUpdate(float ax, float ay, float az, float gx, float gy, float gz, float mx, float my, float mz)
        {
            float q1 = q[0], q2 = q[1], q3 = q[2], q4 = q[3];   // short name local variable for readability
            float norm;
            float hx, hy, bx, bz;
            float vx, vy, vz, wx, wy, wz;
            float ex, ey, ez;
            float pa, pb, pc;

            // Auxiliary variables to avoid repeated arithmetic
            float q1q1 = q1 * q1;
            float q1q2 = q1 * q2;
            float q1q3 = q1 * q3;
            float q1q4 = q1 * q4;
            float q2q2 = q2 * q2;
            float q2q3 = q2 * q3;
            float q2q4 = q2 * q4;
            float q3q3 = q3 * q3;
            float q3q4 = q3 * q4;
            float q4q4 = q4 * q4;   

            // Normalise accelerometer measurement
            norm = sqrt(ax * ax + ay * ay + az * az);
            if (norm == 0.0f) return; // handle NaN
            norm = 1.0f / norm;        // use reciprocal for division
            ax *= norm;
            ay *= norm;
            az *= norm;

            // Normalise magnetometer measurement
            norm = sqrt(mx * mx + my * my + mz * mz);
            if (norm == 0.0f) return; // handle NaN
            norm = 1.0f / norm;        // use reciprocal for division
            mx *= norm;
            my *= norm;
            mz *= norm;

            // Reference direction of Earth's magnetic field
            hx = 2.0f * mx * (0.5f - q3q3 - q4q4) + 2.0f * my * (q2q3 - q1q4) + 2.0f * mz * (q2q4 + q1q3);
            hy = 2.0f * mx * (q2q3 + q1q4) + 2.0f * my * (0.5f - q2q2 - q4q4) + 2.0f * mz * (q3q4 - q1q2);
            bx = sqrt((hx * hx) + (hy * hy));
            bz = 2.0f * mx * (q2q4 - q1q3) + 2.0f * my * (q3q4 + q1q2) + 2.0f * mz * (0.5f - q2q2 - q3q3);

            // Estimated direction of gravity and magnetic field
            vx = 2.0f * (q2q4 - q1q3);
            vy = 2.0f * (q1q2 + q3q4);
            vz = q1q1 - q2q2 - q3q3 + q4q4;
            wx = 2.0f * bx * (0.5f - q3q3 - q4q4) + 2.0f * bz * (q2q4 - q1q3);
            wy = 2.0f * bx * (q2q3 - q1q4) + 2.0f * bz * (q1q2 + q3q4);
            wz = 2.0f * bx * (q1q3 + q2q4) + 2.0f * bz * (0.5f - q2q2 - q3q3);  

            // Error is cross product between estimated direction and measured direction of gravity
            ex = (ay * vz - az * vy) + (my * wz - mz * wy);
            ey = (az * vx - ax * vz) + (mz * wx - mx * wz);
            ez = (ax * vy - ay * vx) + (mx * wy - my * wx);
            if (Ki > 0.0f)
            {
                eInt[0] += ex;      // accumulate integral error
                eInt[1] += ey;
                eInt[2] += ez;
            }
            else
            {
                eInt[0] = 0.0f;     // prevent integral wind up
                eInt[1] = 0.0f;
                eInt[2] = 0.0f;
            }

            // Apply feedback terms
            gx = gx + Kp * ex + Ki * eInt[0];
            gy = gy + Kp * ey + Ki * eInt[1];
            gz = gz + Kp * ez + Ki * eInt[2];

            // Integrate rate of change of quaternion
            pa = q2;
            pb = q3;
            pc = q4;
            q1 = q1 + (-q2 * gx - q3 * gy - q4 * gz) * (0.5f * deltat);
            q2 = pa + (q1 * gx + pb * gz - pc * gy) * (0.5f * deltat);
            q3 = pb + (q1 * gy - pa * gz + pc * gx) * (0.5f * deltat);
            q4 = pc + (q1 * gz + pa * gy - pb * gx) * (0.5f * deltat);

            // Normalise quaternion
            norm = sqrt(q1 * q1 + q2 * q2 + q3 * q3 + q4 * q4);
            norm = 1.0f / norm;
            q[0] = q1 * norm;
            q[1] = q2 * norm;
            q[2] = q3 * norm;
            q[3] = q4 * norm;
 
        }
  };
#endif