File content as of revision 3:c18342e4fddd:

#include "mbed.h"
#include "math.h"
#include "MPU9250.h"


MPU9250::MPU9250(PinName sda, PinName scl, RawSerial* serial_p)
    :
    i2c_p(new I2C(sda,scl)),
    i2c(*i2c_p),
    pc_p(serial_p)
{
    initializeValue();
}

MPU9250::~MPU9250(){}


/*---------- public function ----------*/
bool MPU9250::Initialize(void){
    uint8_t whoami;

    i2c.frequency(400000);                                      // use fast (400 kHz) I2C  
    timer.start();

    whoami = Whoami_MPU9250();
    pc_p->printf("I AM 0x%x\n\r", whoami); pc_p->printf("I SHOULD BE 0x71\n\r");
  
    if(whoami == IAM_MPU9250){
        resetMPU9250();                                                 // Reset registers to default in preparation for device calibration
        calibrateMPU9250(gyroBias, accelBias);  // Calibrate gyro and accelerometers, load biases in bias registers
        wait(1);

        initMPU9250();
        initAK8963(magCalibration);
    
    pc_p->printf("Accelerometer full-scale range = %f  g\n\r", 2.0f*(float)(1<<Ascale));
    pc_p->printf("Gyroscope full-scale range = %f  deg/s\n\r", 250.0f*(float)(1<<Gscale));

    if(Mscale == 0) pc_p->printf("Magnetometer resolution = 14  bits\n\r");
    if(Mscale == 1) pc_p->printf("Magnetometer resolution = 16  bits\n\r");
    if(Mmode == 2) pc_p->printf("Magnetometer ODR = 8 Hz\n\r");
    if(Mmode == 6) pc_p->printf("Magnetometer ODR = 100 Hz\n\r");
    
        getAres();
        getGres();
        getMres();

    pc_p->printf("mpu9250 initialized\r\n");
    return true;
    }else return false;
}

bool MPU9250::sensingAcGyMg(){
    if(readByte(MPU9250_ADDRESS, INT_STATUS) & 0x01) {  // On interrupt, check if data ready interrupt
    sensingAccel();
        sensingGyro();   
        sensingMag();   
    return true;
  }else return false;
}


void MPU9250::calculatePostureAngle(float degree[3]){   
  Now = timer.read_us();
  deltat = (float)((Now - lastUpdate)/1000000.0f); // set integration time by time elapsed since last filter update
  lastUpdate = Now;
    
//  if(lastUpdate - firstUpdate > 10000000.0f) {
//      beta = 0.04;  // decrease filter gain after stabilized
//      zeta = 0.015; // increasey bias drift gain after stabilized
//  }
    
  // Pass gyro rate as rad/s
  MadgwickQuaternionUpdate(ax, ay, az, gx*PI/180.0f, gy*PI/180.0f, gz*PI/180.0f,  my,  mx, mz);
  MahonyQuaternionUpdate(ax, ay, az, gx*PI/180.0f, gy*PI/180.0f, gz*PI/180.0f, my, mx, mz);   //my, mx, mzになってるけどセンサの設置上の都合だろうか
      
  // Define output variables from updated quaternion---these are Tait-Bryan angles, commonly used in aircraft orientation.
  // In this coordinate system, the positive z-axis is down toward Earth. 
  // Yaw is the angle between Sensor x-axis and Earth magnetic North (or true North if corrected for local declination, looking down on the sensor positive yaw is counterclockwise.
  // Pitch is angle between sensor x-axis and Earth ground plane, toward the Earth is positive, up toward the sky is negative.
  // Roll is angle between sensor y-axis and Earth ground plane, y-axis up is positive roll.
  // These arise from the definition of the homogeneous rotation matrix constructed from quaternions.
  // Tait-Bryan angles as well as Euler angles are non-commutative; that is, the get the correct orientation the rotations must be
  // applied in the correct order which for this configuration is yaw, pitch, and then roll.
  // For more see http://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles which has additional links.
  translateQuaternionToDeg(q);
    calibrateDegree();  
    degree[0] = roll;
    degree[1] = pitch;
    degree[2] = yaw;
}


float MPU9250::calculateYawByMg(){
    transformCoordinateFromCompassToMPU();
    lpmag[0] = LPGAIN_MAG *lpmag[0] + (1 - LPGAIN_MAG)*mx;
    lpmag[1] = LPGAIN_MAG *lpmag[1] + (1 - LPGAIN_MAG)*my;
    lpmag[2] = LPGAIN_MAG *lpmag[2] + (1 - LPGAIN_MAG)*mz;
    
    float radroll = PI/180.0f * roll;
    float radpitch = PI/180.0f * pitch;

    return 180.0f/PI * atan2(lpmag[2]*sin(radpitch) - lpmag[1]*cos(radpitch),
                                         lpmag[0]*cos(radroll) - lpmag[1]*sin(radroll)*sin(radpitch) + lpmag[2]*sin(radroll)*cos(radpitch));
}


// Accelerometer and gyroscope self test; check calibration wrt factory settings
void MPU9250::MPU9250SelfTest(float * destination) // Should return percent deviation from factory trim values, +/- 14 or less deviation is a pass
{
    uint8_t rawData[6] = {0, 0, 0, 0, 0, 0};
    uint8_t selfTest[6];
    int16_t gAvg[3], aAvg[3], aSTAvg[3], gSTAvg[3];
    float factoryTrim[6];
    uint8_t FS = 0;
   
    writeByte(MPU9250_ADDRESS, SMPLRT_DIV, 0x00); // Set gyro sample rate to 1 kHz
    writeByte(MPU9250_ADDRESS, CONFIG, 0x02); // Set gyro sample rate to 1 kHz and DLPF to 92 Hz
    writeByte(MPU9250_ADDRESS, GYRO_CONFIG, 1<<FS); // Set full scale range for the gyro to 250 dps
    writeByte(MPU9250_ADDRESS, ACCEL_CONFIG2, 0x02); // Set accelerometer rate to 1 kHz and bandwidth to 92 Hz
    writeByte(MPU9250_ADDRESS, ACCEL_CONFIG, 1<<FS); // Set full scale range for the accelerometer to 2 g

    for( int ii = 0; ii < 200; ii++) { // get average current values of gyro and acclerometer
        readBytes(MPU9250_ADDRESS, ACCEL_XOUT_H, 6, &rawData[0]); // Read the six raw data registers into data array
        aAvg[0] += (int16_t)(((int16_t)rawData[0] << 8) | rawData[1]) ; // Turn the MSB and LSB into a signed 16-bit value
    aAvg[1] += (int16_t)(((int16_t)rawData[2] << 8) | rawData[3]) ;
        aAvg[2] += (int16_t)(((int16_t)rawData[4] << 8) | rawData[5]) ;
        
        readBytes(MPU9250_ADDRESS, GYRO_XOUT_H, 6, &rawData[0]); // Read the six raw data registers sequentially into data array
        gAvg[0] += (int16_t)(((int16_t)rawData[0] << 8) | rawData[1]) ; // Turn the MSB and LSB into a signed 16-bit value
        gAvg[1] += (int16_t)(((int16_t)rawData[2] << 8) | rawData[3]) ;
        gAvg[2] += (int16_t)(((int16_t)rawData[4] << 8) | rawData[5]) ;
    }
  
    for (int ii =0; ii < 3; ii++) { // Get average of 200 values and store as average current readings
        aAvg[ii] /= 200;
        gAvg[ii] /= 200;
    }
  
    // Configure the accelerometer for self-test
    writeByte(MPU9250_ADDRESS, ACCEL_CONFIG, 0xE0); // Enable self test on all three axes and set accelerometer range to +/- 2 g
    writeByte(MPU9250_ADDRESS, GYRO_CONFIG, 0xE0); // Enable self test on all three axes and set gyro range to +/- 250 degrees/s
    //delay(55); // Delay a while to let the device stabilize

    for( int ii = 0; ii < 200; ii++) { // get average self-test values of gyro and acclerometer
        readBytes(MPU9250_ADDRESS, ACCEL_XOUT_H, 6, &rawData[0]); // Read the six raw data registers into data array
        aSTAvg[0] += (int16_t)(((int16_t)rawData[0] << 8) | rawData[1]) ; // Turn the MSB and LSB into a signed 16-bit value
        aSTAvg[1] += (int16_t)(((int16_t)rawData[2] << 8) | rawData[3]) ;
        aSTAvg[2] += (int16_t)(((int16_t)rawData[4] << 8) | rawData[5]) ;
        
        readBytes(MPU9250_ADDRESS, GYRO_XOUT_H, 6, &rawData[0]); // Read the six raw data registers sequentially into data array
        gSTAvg[0] += (int16_t)(((int16_t)rawData[0] << 8) | rawData[1]) ; // Turn the MSB and LSB into a signed 16-bit value
        gSTAvg[1] += (int16_t)(((int16_t)rawData[2] << 8) | rawData[3]) ;
        gSTAvg[2] += (int16_t)(((int16_t)rawData[4] << 8) | rawData[5]) ;
    }
  
    for (int ii =0; ii < 3; ii++) { // Get average of 200 values and store as average self-test readings
        aSTAvg[ii] /= 200;
        gSTAvg[ii] /= 200;
    }
  
 // Configure the gyro and accelerometer for normal operation
    writeByte(MPU9250_ADDRESS, ACCEL_CONFIG, 0x00);
    writeByte(MPU9250_ADDRESS, GYRO_CONFIG, 0x00);
    //delay(45); // Delay a while to let the device stabilize
   
  // Retrieve accelerometer and gyro factory Self-Test Code from USR_Reg
    selfTest[0] = readByte(MPU9250_ADDRESS, SELF_TEST_X_ACCEL); // X-axis accel self-test results
    selfTest[1] = readByte(MPU9250_ADDRESS, SELF_TEST_Y_ACCEL); // Y-axis accel self-test results
    selfTest[2] = readByte(MPU9250_ADDRESS, SELF_TEST_Z_ACCEL); // Z-axis accel self-test results
    selfTest[3] = readByte(MPU9250_ADDRESS, SELF_TEST_X_GYRO); // X-axis gyro self-test results
    selfTest[4] = readByte(MPU9250_ADDRESS, SELF_TEST_Y_GYRO); // Y-axis gyro self-test results
    selfTest[5] = readByte(MPU9250_ADDRESS, SELF_TEST_Z_GYRO); // Z-axis gyro self-test results

    // Retrieve factory self-test value from self-test code reads
    factoryTrim[0] = (float)(2620/1<<FS)*(pow( 1.01 , ((float)selfTest[0] - 1.0) )); // FT[Xa] factory trim calculation
    factoryTrim[1] = (float)(2620/1<<FS)*(pow( 1.01 , ((float)selfTest[1] - 1.0) )); // FT[Ya] factory trim calculation
    factoryTrim[2] = (float)(2620/1<<FS)*(pow( 1.01 , ((float)selfTest[2] - 1.0) )); // FT[Za] factory trim calculation
    factoryTrim[3] = (float)(2620/1<<FS)*(pow( 1.01 , ((float)selfTest[3] - 1.0) )); // FT[Xg] factory trim calculation
    factoryTrim[4] = (float)(2620/1<<FS)*(pow( 1.01 , ((float)selfTest[4] - 1.0) )); // FT[Yg] factory trim calculation
    factoryTrim[5] = (float)(2620/1<<FS)*(pow( 1.01 , ((float)selfTest[5] - 1.0) )); // FT[Zg] factory trim calculation
 
    // Report results as a ratio of (STR - FT)/FT; the change from Factory Trim of the Self-Test Response
    // To get percent, must multiply by 100
    for (int i = 0; i < 3; i++) {
        destination[i] = 100.0*((float)(aSTAvg[i] - aAvg[i]))/factoryTrim[i]; // Report percent differences
        destination[i+3] = 100.0*((float)(gSTAvg[i] - gAvg[i]))/factoryTrim[i+3]; // Report percent differences
    } 
}

void MPU9250::pickupAccel(float accel[3]){
    sensingAccel();
    accel[0] = ax;
    accel[1] = ay;
    accel[2] = az;
}

void MPU9250::pickupGyro(float gyro[3]){
    sensingGyro();
    gyro[0] = gx;
    gyro[1] = gy;
    gyro[2] = gz;
}

void MPU9250::pickupMag(float mag[3]){
    sensingMag();
    mag[0] = mx;
    mag[1] = my;
    mag[2] = mz;
}

float MPU9250::pickupTemp(void){
    sensingTemp();
    return temperature;
}

void MPU9250::displayAccel(void){
    pc_p->printf("ax = %f", 1000*ax); 
  pc_p->printf(" ay = %f", 1000*ay); 
  pc_p->printf(" az = %f  mg\n\r", 1000*az); 
}

void MPU9250::displayGyro(void){
  pc_p->printf("gx = %f", gx); 
  pc_p->printf(" gy = %f", gy); 
  pc_p->printf(" gz = %f  deg/s\n\r", gz); 
}

void MPU9250::displayMag(void){
  pc_p->printf("mx = %f,", mx); 
  pc_p->printf(" my = %f,", my); 
  pc_p->printf(" mz = %f  mG\n\r", mz); 
}

void MPU9250::displayQuaternion(void){
  pc_p->printf("q0 = %f\n\r", q[0]);
  pc_p->printf("q1 = %f\n\r", q[1]);
  pc_p->printf("q2 = %f\n\r", q[2]);
  pc_p->printf("q3 = %f\n\r", q[3]);
}

void MPU9250::displayAngle(void){
    //pc_p->printf("$%d %d %d;",(int)(yaw*100),(int)(pitch*100),(int)(roll*100));
    pc_p->printf("Roll: %f\tPitch: %f\tYaw: %f\n\r",  roll,   pitch,   yaw);
}

void MPU9250::displayTemperature(void){
    pc_p->printf(" temperature = %f  C\n\r", temperature);
}

void MPU9250::setMagBias(float bias_x, float bias_y, float bias_z){
    magbias[0] = bias_x;
    magbias[1] = bias_y;
    magbias[2] = bias_z;
}

/*---------- private function ----------*/

void MPU9250::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 MPU9250::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 MPU9250::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 MPU9250::initializeValue(void){
    Ascale = AFS_2G;     // AFS_2G, AFS_4G, AFS_8G, AFS_16G
    Gscale = GFS_250DPS; // GFS_250DPS, GFS_500DPS, GFS_1000DPS, GFS_2000DPS
    Mscale = MFS_16BITS; // MFS_14BITS or MFS_16BITS, 14-bit or 16-bit magnetometer resolution
    Mmode = 0x06;        // Either 8 Hz 0x02) or 100 Hz (0x06) magnetometer data ODR  

    GyroMeasError = PI * (60.0f / 180.0f);
    beta = sqrt(3.0f / 4.0f) * GyroMeasError;  // compute beta
    GyroMeasDrift = PI * (1.0f / 180.0f);      // gyroscope measurement drift in rad/s/s (start at 0.0 deg/s/s)
    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

    deltat = 0.0f;                             // integration interval for both filter schemes
    lastUpdate = 0, firstUpdate = 0, Now = 0;    // used to calculate integration interval                               // used to calculate integration interval

    for(int i=0; i<3; i++){
        magCalibration[i] = 0;
        gyroBias[i] = 0;
        accelBias[i] = 0;
        magbias[i] = 0;

        eInt[i] = 0.0f; 
    
        lpmag[i] = 0.0f;
    }

    q[0] = 1.0f;
    q[1] = 0.0f;
    q[2] = 0.0f;
    q[3] = 0.0f;
}

void MPU9250::initMPU9250(void)
{  
    // Initialize MPU9250 device
    // wake up device
    writeByte(MPU9250_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(MPU9250_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(MPU9250_ADDRESS, CONFIG, 0x03);  

    // Set sample rate = gyroscope output rate/(1 + SMPLRT_DIV)
    writeByte(MPU9250_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(MPU9250_ADDRESS, GYRO_CONFIG); // get current GYRO_CONFIG register value
    // c = c & ~0xE0; // Clear self-test bits [7:5] 
    c = c & ~0x02; // Clear Fchoice bits [1:0] 
    c = c & ~0x18; // Clear AFS bits [4:3]
    c = c | Gscale << 3; // Set full scale range for the gyro
    // c =| 0x00; // Set Fchoice for the gyro to 11 by writing its inverse to bits 1:0 of GYRO_CONFIG
    writeByte(MPU9250_ADDRESS, GYRO_CONFIG, c ); // Write new GYRO_CONFIG value to register

    // Set accelerometer full-scale range configuration
    c = readByte(MPU9250_ADDRESS, ACCEL_CONFIG); // get current ACCEL_CONFIG register value
    // c = c & ~0xE0; // Clear self-test bits [7:5] 
    c = c & ~0x18;  // Clear AFS bits [4:3]
    c = c | Ascale << 3; // Set full scale range for the accelerometer 
    writeByte(MPU9250_ADDRESS, ACCEL_CONFIG, c); // Write new ACCEL_CONFIG register value

    // Set accelerometer sample rate configuration
    // It is possible to get a 4 kHz sample rate from the accelerometer by choosing 1 for
    // accel_fchoice_b bit [3]; in this case the bandwidth is 1.13 kHz
    c = readByte(MPU9250_ADDRESS, ACCEL_CONFIG2); // get current ACCEL_CONFIG2 register value
    c = c & ~0x0F; // Clear accel_fchoice_b (bit 3) and A_DLPFG (bits [2:0])  
    c = c | 0x03;  // Set accelerometer rate to 1 kHz and bandwidth to 41 Hz
    writeByte(MPU9250_ADDRESS, ACCEL_CONFIG2, c); // Write new ACCEL_CONFIG2 register value

    // 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(MPU9250_ADDRESS, INT_PIN_CFG, 0x22);    
    writeByte(MPU9250_ADDRESS, INT_ENABLE, 0x01);  // Enable data ready (bit 0) interrupt
}

void MPU9250::initAK8963(float * destination)
{
    // First extract the factory calibration for each magnetometer axis
    uint8_t rawData[3];  // x/y/z gyro calibration data stored here

    writeByte(AK8963_ADDRESS, AK8963_CNTL, 0x00); // Power down magnetometer  
    wait(0.01);
    
    writeByte(AK8963_ADDRESS, AK8963_CNTL, 0x0F); // Enter Fuse ROM access mode
    wait(0.01);
  
    readBytes(AK8963_ADDRESS, AK8963_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, etc.
    destination[1] =  (float)(rawData[1] - 128)/256.0f + 1.0f;  
    destination[2] =  (float)(rawData[2] - 128)/256.0f + 1.0f; 
    writeByte(AK8963_ADDRESS, AK8963_CNTL, 0x00); // Power down magnetometer  
    wait(0.01);

    // Configure the magnetometer for continuous read and highest resolution
    // set Mscale bit 4 to 1 (0) to enable 16 (14) bit resolution in CNTL register,
    // and enable continuous mode data acquisition Mmode (bits [3:0]), 0010 for 8 Hz and 0110 for 100 Hz sample rates
    writeByte(AK8963_ADDRESS, AK8963_CNTL, Mscale << 4 | Mmode); // Set magnetometer data resolution and sample ODR
    wait(0.01);
}

void MPU9250::resetMPU9250(void)
{
    // reset device
    writeByte(MPU9250_ADDRESS, PWR_MGMT_1, 0x80); // Write a one to bit 7 reset bit; toggle reset device
    wait(0.1);
}

// 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 MPU9250::calibrateMPU9250(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};
    int32_t accel_bias_reg[3] = {0, 0, 0}; // A place to hold the factory accelerometer trim biases
  
    // reset device, reset all registers, clear gyro and accelerometer bias registers
    writeByte(MPU9250_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(MPU9250_ADDRESS, PWR_MGMT_1, 0x01);  
    writeByte(MPU9250_ADDRESS, PWR_MGMT_2, 0x00); 
    wait(0.2);

    // Configure device for bias calculation
    writeByte(MPU9250_ADDRESS, INT_ENABLE, 0x00);   // Disable all interrupts
    writeByte(MPU9250_ADDRESS, FIFO_EN, 0x00);      // Disable FIFO
    writeByte(MPU9250_ADDRESS, PWR_MGMT_1, 0x00);   // Turn on internal clock source
    writeByte(MPU9250_ADDRESS, I2C_MST_CTRL, 0x00); // Disable I2C master
    writeByte(MPU9250_ADDRESS, USER_CTRL, 0x00);    // Disable FIFO and I2C master modes
    writeByte(MPU9250_ADDRESS, USER_CTRL, 0x0C);    // Reset FIFO and DMP
    wait(0.015);
  
    // Configure MPU9250 gyro and accelerometer for bias calculation
    writeByte(MPU9250_ADDRESS, CONFIG, 0x01);      // Set low-pass filter to 188 Hz
    writeByte(MPU9250_ADDRESS, SMPLRT_DIV, 0x00);  // Set sample rate to 1 kHz
    writeByte(MPU9250_ADDRESS, GYRO_CONFIG, 0x00);  // Set gyro full-scale to 250 degrees per second, maximum sensitivity
    writeByte(MPU9250_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(MPU9250_ADDRESS, USER_CTRL, 0x40);   // Enable FIFO  
    writeByte(MPU9250_ADDRESS, FIFO_EN, 0x78);     // Enable gyro and accelerometer sensors for FIFO (max size 512 bytes in MPU-9250)
    wait(0.04); // accumulate 40 samples in 80 milliseconds = 480 bytes

    // At end of sample accumulation, turn off FIFO sensor read
    writeByte(MPU9250_ADDRESS, FIFO_EN, 0x00);        // Disable gyro and accelerometer sensors for FIFO
    readBytes(MPU9250_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(MPU9250_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(MPU9250_ADDRESS, XG_OFFSET_H, data[0]);
    writeByte(MPU9250_ADDRESS, XG_OFFSET_L, data[1]);
    writeByte(MPU9250_ADDRESS, YG_OFFSET_H, data[2]);
    writeByte(MPU9250_ADDRESS, YG_OFFSET_L, data[3]);
    writeByte(MPU9250_ADDRESS, ZG_OFFSET_H, data[4]);
    writeByte(MPU9250_ADDRESS, ZG_OFFSET_L, 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.

    readBytes(MPU9250_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(MPU9250_ADDRESS, YA_OFFSET_H, 2, &data[0]);
    accel_bias_reg[1] = (int16_t) ((int16_t)data[0] << 8) | data[1];
    readBytes(MPU9250_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(MPU9250_ADDRESS, XA_OFFSET_H, data[0]);
    writeByte(MPU9250_ADDRESS, XA_OFFSET_L, data[1]);
    writeByte(MPU9250_ADDRESS, YA_OFFSET_H, data[2]);
    writeByte(MPU9250_ADDRESS, YA_OFFSET_L, data[3]);
    writeByte(MPU9250_ADDRESS, ZA_OFFSET_H, data[4]);
    writeByte(MPU9250_ADDRESS, ZA_OFFSET_L, 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;
}

void MPU9250::getMres(void)
{
    switch (Mscale)
    {
        // Possible magnetometer scales (and their register bit settings) are:
        // 14 bit resolution (0) and 16 bit resolution (1)
        case MFS_14BITS:
                mRes = 10.0*4219.0/8190.0; // Proper scale to return milliGauss
                break;
        case MFS_16BITS:
                mRes = 10.0*4219.0/32760.0; // Proper scale to return milliGauss
                break;
  }
}

void MPU9250::getGres(void) {
    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 MPU9250::getAres(void) 
{
    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 MPU9250::readAccelData(int16_t * destination)
{
    uint8_t rawData[6];  // x/y/z accel register data stored here
  
    readBytes(MPU9250_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 MPU9250::readGyroData(int16_t * destination)
{
    uint8_t rawData[6];  // x/y/z gyro register data stored here
  
    readBytes(MPU9250_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 MPU9250::readMagData(int16_t * destination)
{
    uint8_t rawData[7];  // x/y/z gyro register data, ST2 register stored here, must read ST2 at end of data acquisition
  
    if(readByte(AK8963_ADDRESS, AK8963_ST1) & 0x01) { // wait for magnetometer data ready bit to be set
        readBytes(AK8963_ADDRESS, AK8963_XOUT_L, 7, &rawData[0]);  // Read the six raw data and ST2 registers sequentially into data array
        uint8_t c = rawData[6]; // End data read by reading ST2 register
        if(!(c & 0x08)) { // Check if magnetic sensor overflow set, if not then report data
            destination[0] = (int16_t)(((int16_t)rawData[1] << 8) | rawData[0]);  // Turn the MSB and LSB into a signed 16-bit value
            destination[1] = (int16_t)(((int16_t)rawData[3] << 8) | rawData[2]) ;  // Data stored as little Endian
            destination[2] = (int16_t)(((int16_t)rawData[5] << 8) | rawData[4]) ; 
        }
    }
}

int16_t MPU9250::readTempData(void)
{
  uint8_t rawData[2];  // x/y/z gyro register data stored here
  
  readBytes(MPU9250_ADDRESS, TEMP_OUT_H, 2, &rawData[0]);  // Read the two raw data registers sequentially into data array 
  
  return (int16_t)(((int16_t)rawData[0]) << 8 | rawData[1]) ;  // Turn the MSB and LSB into a 16-bit value
}

uint8_t MPU9250::Whoami_MPU9250(void){
    return readByte(MPU9250_ADDRESS, WHO_AM_I_MPU9250);
}

uint8_t MPU9250::Whoami_AK8963(void){
    return readByte(WHO_AM_I_AK8963, WHO_AM_I_AK8963);
}

void MPU9250::sensingAccel(void){
    readAccelData(accelCount);
    ax = (float)accelCount[0]*aRes - accelBias[0];
    ay = (float)accelCount[1]*aRes - accelBias[1];   
    az = (float)accelCount[2]*aRes - accelBias[2];
}

void MPU9250::sensingGyro(void){
    readGyroData(gyroCount);
    gx = (float)gyroCount[0]*gRes - gyroBias[0];
    gy = (float)gyroCount[1]*gRes - gyroBias[1];  
    gz = (float)gyroCount[2]*gRes - gyroBias[2];   
}

void MPU9250::sensingMag(void){
    readMagData(magCount);
    mx = (float)magCount[0]*mRes*magCalibration[0] - magbias[0];
    my = (float)magCount[1]*mRes*magCalibration[1] - magbias[1];  
    mz = (float)magCount[2]*mRes*magCalibration[2] - magbias[2];
}

void MPU9250::sensingTemp(void){
    tempCount = readTempData();
  temperature = ((float) tempCount) / 333.87f + 21.0f; // Temperature in degrees Centigrade
}

// 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 MPU9250::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;

}

void MPU9250::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;

}

void MPU9250::translateQuaternionToDeg(float quaternion[4]){
  yaw   = atan2(2.0f * (quaternion[1] * quaternion[2] + quaternion[0] * quaternion[3]), quaternion[0] * quaternion[0] + quaternion[1] * quaternion[1] - quaternion[2] * quaternion[2] - quaternion[3] * quaternion[3]);   
  roll = -asin(2.0f * (quaternion[1] * quaternion[3] - quaternion[0] * quaternion[2]));
  pitch  = atan2(2.0f * (quaternion[0] * quaternion[1] + quaternion[2] * quaternion[3]), quaternion[0] * quaternion[0] - quaternion[1] * quaternion[1] - quaternion[2] * quaternion[2] + quaternion[3] * quaternion[3]);
}

void MPU9250::calibrateDegree(void){
    pitch *= 180.0f / PI;
  yaw   *= 180.0f / PI; 
  yaw   -= DECLINATION;
  roll  *= 180.0f / PI; 
}

void MPU9250::transformCoordinateFromCompassToMPU(){
    float buf = mx;
    mx = my;
    my = buf;
    mz = -mz;
}