File content as of revision 0:5a3104f02775:

#include"MPU9255.h"

//-----------------
//private functions
//-----------------

void MPU9255::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 MPU9255::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 MPU9255::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];
    }
} 


//----------------
//public functions
//----------------

MPU9255::MPU9255(PinName sda, PinName scl, RawSerial* serial_p)
    : i2c_p(new I2C(sda,scl)), i2c(*i2c_p), pc_p(serial_p)
{
    i2c.frequency(40000);
}

MPU9255::~MPU9255() {}

uint8_t MPU9255::whoami_mpu9255()
{
    uint8_t a = readByte(MPU9255_ADDRESS, WHO_AM_I_MPU9255);
    return a;
}

void MPU9255::reset_mpu9255()
{
    writeByte(MPU9255_ADDRESS, PWR_MGMT_1, 0x80);
    wait_ms(10);
}

void MPU9255::selftest_mpu9255(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];
    int32_t gAvg[3] = {0}, aAvg[3] = {0}, aSTAvg[3] = {0}, gSTAvg[3] = {0};
    float factoryTrim[6];
    uint8_t FS = 0;
   
    writeByte(MPU9255_ADDRESS, SMPLRT_DIV, 0x00);    // Set gyro sample rate to 1 kHz
    writeByte(MPU9255_ADDRESS, CONFIG, 0x02);        // Set gyro sample rate to 1 kHz and DLPF to 92 Hz
    writeByte(MPU9255_ADDRESS, GYRO_CONFIG, 1<<FS);  // Set full scale range for the gyro to 250 dps
    writeByte(MPU9255_ADDRESS, ACCEL_CONFIG2, 0x02); // Set accelerometer rate to 1 kHz and bandwidth to 92 Hz
    writeByte(MPU9255_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(MPU9255_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(MPU9255_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(MPU9255_ADDRESS, ACCEL_CONFIG, 0xE0); // Enable self test on all three axes and set accelerometer range to +/- 2 g
    writeByte(MPU9255_ADDRESS, GYRO_CONFIG,  0xE0); // Enable self test on all three axes and set gyro range to +/- 250 degrees/s
    wait_ms(25);  // 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(MPU9255_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(MPU9255_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(MPU9255_ADDRESS, ACCEL_CONFIG, 0x00);  
    writeByte(MPU9255_ADDRESS, GYRO_CONFIG,  0x00);  
    wait_ms(25);  // Delay a while to let the device stabilize
   
   // Retrieve accelerometer and gyro factory Self-Test Code from USR_Reg
    selfTest[0] = readByte(MPU9255_ADDRESS, SELF_TEST_X_ACCEL); // X-axis accel self-test results
    selfTest[1] = readByte(MPU9255_ADDRESS, SELF_TEST_Y_ACCEL); // Y-axis accel self-test results
    selfTest[2] = readByte(MPU9255_ADDRESS, SELF_TEST_Z_ACCEL); // Z-axis accel self-test results
    selfTest[3] = readByte(MPU9255_ADDRESS, SELF_TEST_X_GYRO);  // X-axis gyro self-test results
    selfTest[4] = readByte(MPU9255_ADDRESS, SELF_TEST_Y_GYRO);  // Y-axis gyro self-test results
    selfTest[5] = readByte(MPU9255_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]   = 100.0f*((float)(aSTAvg[i] - aAvg[i]))/factoryTrim[i] - 100.0f;   // Report percent differences
        destination[i+3] = 100.0f*((float)(gSTAvg[i] - gAvg[i]))/factoryTrim[i+3] - 100.0f; // Report percent differences
    }
   
}

float MPU9255::getMres(uint8_t Mscale) 
{
    float _mRes;
    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.*4912./8190.; // Proper scale to return milliGauss
            return _mRes;
            //break;
        case MFS_16BITS:
            _mRes = 10.*4912./32760.0; // Proper scale to return milliGauss (4912/32760=0.15)
            return _mRes;              // convert 'μT' to 'mG' 
            //break;
    }
}

float MPU9255::getGres(uint8_t Gscale)
{
    float _gRes;
    switch (Gscale)
    {
  // Possible gyro scales (and their register bit settings) are:
  // 250 DPS (00), 500 DPS (01), 1000 DPS (10), and 2000 DPS  (11). 
        case GFS_250DPS:
            _gRes = 250.0/32768.0;
            return _gRes;
            //break;
        case GFS_500DPS:
            _gRes = 500.0/32768.0;
            return _gRes;
            //break;
        case GFS_1000DPS:
            _gRes = 1000.0/32768.0;
            return _gRes;
            //break;
        case GFS_2000DPS:
            _gRes = 2000.0/32768.0;
            return _gRes;
            //break;
    }
}

float MPU9255::getAres(uint8_t Ascale)
{
    float _aRes;
    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 = 2.0f/32768.0f;
            return _aRes;
            //break;
        case AFS_4G:
            _aRes = 4.0f/32768.0f;
            return _aRes;
            //break;
        case AFS_8G:
            _aRes = 8.0f/32768.0f;
            return _aRes;
            //break;
        case AFS_16G:
            _aRes = 16.0f/32768.0f;
            return _aRes;
            //break;
    }
}

void MPU9255::calibrate_mpu9255(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
    writeByte(MPU9255_ADDRESS, PWR_MGMT_1, 0x80); // Write a one to bit 7 reset bit; toggle reset device
    wait_ms(100);
   
    // get stable time source; Auto select clock source to be PLL gyroscope reference if ready 
    // else use the internal oscillator, bits 2:0 = 001
    writeByte(MPU9255_ADDRESS, PWR_MGMT_1, 0x01);  
    writeByte(MPU9255_ADDRESS, PWR_MGMT_2, 0x00);
    wait_ms(200);                                    

    // Configure device for bias calculation
    writeByte(MPU9255_ADDRESS, INT_ENABLE, 0x00);   // Disable all interrupts
    writeByte(MPU9255_ADDRESS, FIFO_EN, 0x00);      // Disable FIFO
    writeByte(MPU9255_ADDRESS, PWR_MGMT_1, 0x00);   // Turn on internal clock source
    writeByte(MPU9255_ADDRESS, I2C_MST_CTRL, 0x00); // Disable I2C master
    writeByte(MPU9255_ADDRESS, USER_CTRL, 0x00);    // Disable FIFO and I2C master modes
    writeByte(MPU9255_ADDRESS, USER_CTRL, 0x0C);    // Reset FIFO and DMP
    wait_ms(15);
  
    // Configure MPU6050 gyro and accelerometer for bias calculation
    writeByte(MPU9255_ADDRESS, CONFIG, 0x01);      // Set low-pass filter to 188 Hz
    writeByte(MPU9255_ADDRESS, SMPLRT_DIV, 0x00);  // Set sample rate to 1 kHz
    writeByte(MPU9255_ADDRESS, GYRO_CONFIG, 0x00);  // Set gyro full-scale to 250 degrees per second, maximum sensitivity
    writeByte(MPU9255_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(MPU9255_ADDRESS, USER_CTRL, 0x40);   // Enable FIFO  
    writeByte(MPU9255_ADDRESS, FIFO_EN, 0x78);     // Enable gyro and accelerometer sensors for FIFO  (max size 512 bytes in MPU-9150)
    wait_ms(40); // accumulate 40 samples in 40 milliseconds = 480 bytes

// At end of sample accumulation, turn off FIFO sensor read
    writeByte(MPU9255_ADDRESS, FIFO_EN, 0x00);        // Disable gyro and accelerometer sensors for FIFO
    readBytes(MPU9255_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(MPU9255_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(MPU9255_ADDRESS, XG_OFFSET_H, data[0]);
    writeByte(MPU9255_ADDRESS, XG_OFFSET_L, data[1]);
    writeByte(MPU9255_ADDRESS, YG_OFFSET_H, data[2]);
    writeByte(MPU9255_ADDRESS, YG_OFFSET_L, data[3]);
    writeByte(MPU9255_ADDRESS, ZG_OFFSET_H, data[4]);
    writeByte(MPU9255_ADDRESS, ZG_OFFSET_L, data[5]);
  
// Output scaled gyro biases for display in the main program
    dest1[0] = (float) gyro_bias[0]/(float) gyrosensitivity;  
    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(MPU9255_ADDRESS, XA_OFFSET_H, 2, &data[0]); // Read factory accelerometer trim values
    accel_bias_reg[0] = (int32_t) (((int16_t)data[0] << 8) | data[1]);
    readBytes(MPU9255_ADDRESS, YA_OFFSET_H, 2, &data[0]);
    accel_bias_reg[1] = (int32_t) (((int16_t)data[0] << 8) | data[1]);
    readBytes(MPU9255_ADDRESS, ZA_OFFSET_H, 2, &data[0]);
    accel_bias_reg[2] = (int32_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-9255
// Are we handling the temperature correction bit properly?
// Push accelerometer biases to hardware registers
//  writeByte(MPU9255_ADDRESS, XA_OFFSET_H, data[0]);
//  writeByte(MPU9255_ADDRESS, XA_OFFSET_L, data[1]);
//  writeByte(MPU9255_ADDRESS, YA_OFFSET_H, data[2]);
//  writeByte(MPU9255_ADDRESS, YA_OFFSET_L, data[3]);
//  writeByte(MPU9255_ADDRESS, ZA_OFFSET_H, data[4]);
//  writeByte(MPU9255_ADDRESS, ZA_OFFSET_L, data[5]);

// Output scaled accelerometer biases for display 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 MPU9255::init_mpu9255(uint8_t Ascale, uint8_t Gscale, uint8_t sampleRate)
{  
 // wake up device
    writeByte(MPU9255_ADDRESS, PWR_MGMT_1, 0x00); // Clear sleep mode bit (6), enable all sensors 
    wait_ms(100); // Wait for all registers to reset 

 // get stable time source
    writeByte(MPU9255_ADDRESS, PWR_MGMT_1, 0x01);  // Auto select clock source to be PLL gyroscope reference if ready else
    wait_ms(200); 
  
 // Configure Gyro and Thermometer
 // Disable FSYNC and set thermometer and gyro bandwidth to 41 and 42 Hz, respectively; 
 // minimum delay time for this setting is 5.9 ms, which means sensor fusion update rates cannot
 // be higher than 1 / 0.0059 = 170 Hz
 // DLPF_CFG = bits 2:0 = 011; this limits the sample rate to 1000 Hz for both
 // With the MPU9255, it is possible to get gyro sample rates of 32 kHz (!), 8 kHz, or 1 kHz
    writeByte(MPU9255_ADDRESS, CONFIG, 0x03);  

 // Set sample rate = gyroscope output rate/(1 + SMPLRT_DIV)
    writeByte(MPU9255_ADDRESS, SMPLRT_DIV, sampleRate);  // Use a 200 Hz rate; a rate consistent with the filter update rate 
                                                       // determined inset 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(MPU9255_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(MPU9255_ADDRESS, GYRO_CONFIG, c ); // Write new GYRO_CONFIG value to register
  
 // Set accelerometer full-scale range configuration
    c = readByte(MPU9255_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(MPU9255_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(MPU9255_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(MPU9255_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, hold interrupt pin level HIGH until interrupt cleared,
  // clear on read of INT_STATUS, and enable I2C_BYPASS_EN so additional chips 
  // can join the I2C bus and all can be controlled by the Arduino as master
    writeByte(MPU9255_ADDRESS, INT_PIN_CFG, 0x10);  // INT is 50 microsecond pulse and any read to clear  
    writeByte(MPU9255_ADDRESS, INT_ENABLE, 0x01);  // Enable data ready (bit 0) interrupt
    wait_ms(100);
 
    writeByte(MPU9255_ADDRESS, USER_CTRL, 0x20);          // Enable I2C Master mode  
    writeByte(MPU9255_ADDRESS, I2C_MST_CTRL, 0x1D);       // I2C configuration STOP after each transaction, master I2C bus at 400 KHz
    writeByte(MPU9255_ADDRESS, I2C_MST_DELAY_CTRL, 0x81); // Use blocking data retreival and enable delay for mag sample rate mismatch
    writeByte(MPU9255_ADDRESS, I2C_SLV4_CTRL, 0x01);      // Delay mag data retrieval to once every other accel/gyro data sample
}


uint8_t MPU9255::get_AK8963CID()
{
    writeByte(MPU9255_ADDRESS, USER_CTRL, 0x20);    // Enable I2C Master mode  
    writeByte(MPU9255_ADDRESS, I2C_MST_CTRL, 0x0D); // I2C configuration multi-master I2C 400KHz

    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS | 0x80);    // Set the I2C slave address of AK8963 and set for read.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, WHO_AM_I_AK8963);           // I2C slave 0 register address from where to begin data transfer
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x81);                     // Enable I2C and transfer 1 byte
    wait_ms(10);
    uint8_t c = readByte(MPU9255_ADDRESS, EXT_SENS_DATA_00);             // Read the WHO_AM_I byte
    return c;
}

void MPU9255::init_AK8963Slave(uint8_t Mscale, uint8_t Mmode, float * magCalibration)
{
   // First extract the factory calibration for each magnetometer axis
    uint8_t rawData[3];  // x/y/z gyro calibration data stored here

    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS);           // Set the I2C slave address of AK8963 and set for write.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, AK8963_CNTL2);              // I2C slave 0 register address from where to begin data transfer
    writeByte(MPU9255_ADDRESS, I2C_SLV0_DO, 0x01);                       // Reset AK8963
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x81);                     // Enable I2C and write 1 byte
    wait_ms(50);
    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS);           // Set the I2C slave address of AK8963 and set for write.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, AK8963_CNTL);               // I2C slave 0 register address from where to begin data transfer
    writeByte(MPU9255_ADDRESS, I2C_SLV0_DO, 0x00);                       // Power down magnetometer  
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x81);                     // Enable I2C and write 1 byte
    wait_ms(50);
    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS);           // Set the I2C slave address of AK8963 and set for write.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, AK8963_CNTL);               // I2C slave 0 register address from where to begin data transfer
    writeByte(MPU9255_ADDRESS, I2C_SLV0_DO, 0x0F);                       // Enter fuze mode
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x81);                     // Enable I2C and write 1 byte
    wait_ms(50);
   
    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS | 0x80);    // Set the I2C slave address of AK8963 and set for read.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, AK8963_ASAX);               // I2C slave 0 register address from where to begin data transfer
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x83);                     // Enable I2C and read 3 bytes
    wait_ms(50);
    readBytes(MPU9255_ADDRESS, EXT_SENS_DATA_00, 3, &rawData[0]);        // Read the x-, y-, and z-axis calibration values
    magCalibration[0] =  (float)(rawData[0] - 128)/256.0f + 1.0f;        // Return x-axis sensitivity adjustment values, etc.
    magCalibration[1] =  (float)(rawData[1] - 128)/256.0f + 1.0f;  
    magCalibration[2] =  (float)(rawData[2] - 128)/256.0f + 1.0f; 
    /*_magCalibration[0] = magCalibration[0];
    _magCalibration[1] = magCalibration[1];
    _magCalibration[2] = magCalibration[2];
    _Mmode = Mmode;*/
    
    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS);           // Set the I2C slave address of AK8963 and set for write.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, AK8963_CNTL);               // I2C slave 0 register address from where to begin data transfer
    writeByte(MPU9255_ADDRESS, I2C_SLV0_DO, 0x00);                       // Power down magnetometer  
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x81);                     // Enable I2C and transfer 1 byte
    wait_ms(50);

    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS);           // Set the I2C slave address of AK8963 and set for write.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, AK8963_CNTL);               // I2C slave 0 register address from where to begin data transfer 
    // 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(MPU9255_ADDRESS, I2C_SLV0_DO, Mscale << 4 | Mmode);        // Set magnetometer data resolution and sample ODR
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x81);                     // Enable I2C and transfer 1 byte
    wait_ms(50);
    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS | 0x80);    // Set the I2C slave address of AK8963 and set for read.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, AK8963_CNTL);               // I2C slave 0 register address from where to begin data transfer
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x81);                     // Enable I2C and transfer 1 byte
    wait_ms(50);
}

void MPU9255::readMagData_mpu9255(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
//  readBytes(AK8963_ADDRESS, AK8963_XOUT_L, 7, &rawData[0]);  // Read the six raw data and ST2 registers sequentially into data array
    writeByte(MPU9255_ADDRESS, I2C_SLV0_ADDR, AK8963_ADDRESS | 0x80);    // Set the I2C slave address of AK8963 and set for read.
    writeByte(MPU9255_ADDRESS, I2C_SLV0_REG, AK8963_XOUT_L);             // I2C slave 0 register address from where to begin data transfer
    writeByte(MPU9255_ADDRESS, I2C_SLV0_CTRL, 0x87);                     // Enable I2C and read 7 bytes
    wait_ms(2);
    readBytes(MPU9255_ADDRESS, EXT_SENS_DATA_00, 7, &rawData[0]);        // Read the x-, y-, and z-axis calibration values
    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)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] ;  // Data stored as little Endian
        destination[2] = ((int16_t)rawData[5] << 8) | rawData[4] ; 
    }
}

void MPU9255::readaccgyrodata_mpu9255(int16_t * destination)
{
    uint8_t rawData[14];  // x/y/z accel register data stored here
    readBytes(MPU9255_ADDRESS, ACCEL_XOUT_H, 14, &rawData[0]);  // Read the 14 raw data registers into data array
    destination[0] = ((int16_t)rawData[0] << 8) | rawData[1] ;  // Turn the MSB and LSB into a signed 16-bit value
    destination[1] = ((int16_t)rawData[2] << 8) | rawData[3] ;  
    destination[2] = ((int16_t)rawData[4] << 8) | rawData[5] ; 
    destination[3] = ((int16_t)rawData[6] << 8) | rawData[7] ;   
    destination[4] = ((int16_t)rawData[8] << 8) | rawData[9] ;  
    destination[5] = ((int16_t)rawData[10] << 8) | rawData[11] ;  
    destination[6] = ((int16_t)rawData[12] << 8) | rawData[13] ; 
}