File content as of revision 2:a17f66569378:

#include <mbed.h>
#include "MPU9250.h"


mpu9250::mpu9250(PinName _sda, PinName _scl, uint8_t address) : i2c(_sda, _scl)
{    
    MPU9250_ADDRESS = address << 1;
    i2c.frequency(400000);
}


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];
    }
}

bool mpu9250::alive()
{
    if(readByte(MPU9250_ADDRESS, WHO_AM_I_MPU9250) == 0x71)
        return true;
    else
        return false;
}

void mpu9250::getGres(uint8_t Gscale)
{
    switch (Gscale) {
        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(uint8_t Ascale)
{
    switch (Ascale) {
        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::readTempData(int16_t * destination)
{
    uint8_t rawData[2];
    readBytes(MPU9250_ADDRESS, TEMP_OUT_H, 2, &rawData[0]);  // Read the two 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 16-bit value
}

void mpu9250::readAll(int16_t * destinationAcc, int16_t * destinationGyro, int16_t * destinationTemp)
{
    readAccelData(destinationAcc);  // Read the x/y/z adc values
    readGyroData(destinationGyro);  // Read the x/y/z adc values
    readTempData(destinationTemp);  // Read the adc values
}

void mpu9250::ReadConvertAll(float * destinationAcc, float * destinationGyro, float * destinationTemp)
{
    int16_t AccRead[3];
    int16_t GyroRead[3];
    int16_t TempRead[1];

    readAll(AccRead,GyroRead,TempRead);

    destinationAcc[0] = -1000*((float)AccRead[1]*aRes - accelBias[1]);  // get actual g value, this depends on scale being set
    destinationAcc[1] = -1000*((float)AccRead[0]*aRes - accelBias[0]);
    destinationAcc[2] = 1000*((float)AccRead[2]*aRes - accelBias[2]);

    destinationGyro[0] = (float)GyroRead[0]*gRes - gyroBias[0];  // get actual gyro value, this depends on scale being set
    destinationGyro[1] = (float)GyroRead[1]*gRes - gyroBias[1];
    destinationGyro[2] = (float)GyroRead[2]*gRes - gyroBias[2];

    destinationTemp[0] = ((float) TempRead[0]) / 333.87f + 21.0f; // Temperature in degrees Centigrade
}

void mpu9250::resetMPU9250()
{
    writeByte(MPU9250_ADDRESS, PWR_MGMT_1, 0x80); // Write a one to bit 7 reset bit; toggle reset device
    wait(0.1);
}

void mpu9250::initMPU9250(uint8_t Ascale,uint8_t Gscale)
{
    resetMPU9250();
    wait(0.2);

    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

    writeByte(MPU9250_ADDRESS, PWR_MGMT_1, 0x01);  // Set clock source to be PLL with x-axis gyroscope reference, bits 2:0 = 001
    writeByte(MPU9250_ADDRESS, CONFIG, 0x03);

    writeByte(MPU9250_ADDRESS, SMPLRT_DIV, 0x04);  // Use a 200 Hz rate; the same rate set in CONFIG above

    uint8_t c =  readByte(MPU9250_ADDRESS, GYRO_CONFIG);
    writeByte(MPU9250_ADDRESS, GYRO_CONFIG, c & ~0xE0); // Clear self-test bits [7:5]
    writeByte(MPU9250_ADDRESS, GYRO_CONFIG, c & ~0x18); // Clear AFS bits [4:3]
    writeByte(MPU9250_ADDRESS, GYRO_CONFIG, c | Gscale); // Set full scale range for the gyro

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

    c = readByte(MPU9250_ADDRESS, ACCEL_CONFIG2);
    writeByte(MPU9250_ADDRESS, ACCEL_CONFIG2, c & ~0x0F); // Clear accel_fchoice_b (bit 3) and A_DLPFG (bits [2:0])
    writeByte(MPU9250_ADDRESS, ACCEL_CONFIG2, c | 0x03); // Set accelerometer rate to 1 kHz and bandwidth to 41 Hz

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

    getAres(Ascale); // Get accelerometer sensitivity
    getGres(Gscale); // Get gyro sensitivity

    calibrateMPU9250(gyroBias, accelBias); // Calibrate gyro and accelerometers, load biases in 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};

    writeByte(MPU9250_ADDRESS, PWR_MGMT_1, 0x80); // Write a one to bit 7 reset bit; toggle reset device
    wait(0.1);

    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;

    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;

    int32_t accel_bias_reg[3] = {0, 0, 0}; // A place to hold the factory accelerometer trim biases
    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

    // 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;
}