ardupilot/libraries/AP_InertialSensor/AP_InertialSensor_MPU9250.cpp

/*
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
#include <AP_HAL/AP_HAL.h>

#include "AP_InertialSensor_MPU9250.h"

#include <assert.h>
#include <utility>
#include <stdio.h>

#include <AP_HAL/GPIO.h>

extern const AP_HAL::HAL &hal;

// MPU9250 accelerometer scaling for 16g range
#define MPU9250_ACCEL_SCALE_1G    (GRAVITY_MSS / 2048.0f)

#define MPUREG_XG_OFFS_TC                               0x00
#define MPUREG_YG_OFFS_TC                               0x01
#define MPUREG_ZG_OFFS_TC                               0x02
#define MPUREG_X_FINE_GAIN                              0x03
#define MPUREG_Y_FINE_GAIN                              0x04
#define MPUREG_Z_FINE_GAIN                              0x05

// MPU9250 registers
#define MPUREG_XA_OFFS_H                                0x77    // X axis accelerometer offset (high byte)
#define MPUREG_XA_OFFS_L                                0x78    // X axis accelerometer offset (low byte)
#define MPUREG_YA_OFFS_H                                0x7A    // Y axis accelerometer offset (high byte)
#define MPUREG_YA_OFFS_L                                0x0B    // Y axis accelerometer offset (low byte)
#define MPUREG_ZA_OFFS_H                                0x0D    // Z axis accelerometer offset (high byte)
#define MPUREG_ZA_OFFS_L                                0x0E    // Z axis accelerometer offset (low byte)

// MPU9250 registers
#define MPUREG_XG_OFFS_USRH                     0x13    // X axis gyro offset (high byte)
#define MPUREG_XG_OFFS_USRL                     0x14    // X axis gyro offset (low byte)
#define MPUREG_YG_OFFS_USRH                     0x15    // Y axis gyro offset (high byte)
#define MPUREG_YG_OFFS_USRL                     0x16    // Y axis gyro offset (low byte)
#define MPUREG_ZG_OFFS_USRH                     0x17    // Z axis gyro offset (high byte)
#define MPUREG_ZG_OFFS_USRL                     0x18    // Z axis gyro offset (low byte)
#define MPUREG_SMPLRT_DIV                               0x19    // sample rate.  Fsample= 1Khz/(<this value>+1) = 200Hz
#       define MPUREG_SMPLRT_1000HZ                             0x00
#       define MPUREG_SMPLRT_500HZ                              0x01
#       define MPUREG_SMPLRT_250HZ                              0x03
#       define MPUREG_SMPLRT_200HZ                              0x04
#       define MPUREG_SMPLRT_100HZ                              0x09
#       define MPUREG_SMPLRT_50HZ                               0x13
#define MPUREG_CONFIG                                           0x1A
#define MPUREG_GYRO_CONFIG                                      0x1B
// bit definitions for MPUREG_GYRO_CONFIG
#       define BITS_GYRO_FS_250DPS                              0x00
#       define BITS_GYRO_FS_500DPS                              0x08
#       define BITS_GYRO_FS_1000DPS                             0x10
#       define BITS_GYRO_FS_2000DPS                             0x18
#       define BITS_GYRO_FS_MASK                                0x18    // only bits 3 and 4 are used for gyro full scale so use this to mask off other bits
#       define BITS_GYRO_ZGYRO_SELFTEST                 0x20
#       define BITS_GYRO_YGYRO_SELFTEST                 0x40
#       define BITS_GYRO_XGYRO_SELFTEST                 0x80
#define MPUREG_ACCEL_CONFIG                             0x1C
#define MPUREG_ACCEL_CONFIG2                            0x1D
#define MPUREG_MOT_THR                                  0x1F    // detection threshold for Motion interrupt generation.  Motion is detected when the absolute value of any of the accelerometer measurements exceeds this
#define MPUREG_MOT_DUR                                  0x20    // duration counter threshold for Motion interrupt generation. The duration counter ticks at 1 kHz, therefore MOT_DUR has a unit of 1 LSB = 1 ms
#define MPUREG_ZRMOT_THR                                0x21    // detection threshold for Zero Motion interrupt generation.
#define MPUREG_ZRMOT_DUR                                0x22    // duration counter threshold for Zero Motion interrupt generation. The duration counter ticks at 16 Hz, therefore ZRMOT_DUR has a unit of 1 LSB = 64 ms.
#define MPUREG_FIFO_EN                                  0x23
#       define BIT_TEMP_FIFO_EN                                0x80
#       define BIT_XG_FIFO_EN                                  0x40
#       define BIT_YG_FIFO_EN                                  0x20
#       define BIT_ZG_FIFO_EN                                  0x10
#       define BIT_ACCEL_FIFO_EN                               0x08
#       define BIT_SLV2_FIFO_EN                                0x04
#       define BIT_SLV1_FIFO_EN                                0x02
#       define BIT_SLV0_FIFI_EN0                               0x01
#define MPUREG_INT_PIN_CFG                              0x37
#       define BIT_INT_RD_CLEAR                                 0x10    // clear the interrupt when any read occurs
#       define BIT_LATCH_INT_EN                                 0x20    // latch data ready pin
#       define BIT_BYPASS_EN                                    0x02    // connect auxiliary I2C bus to the main I2C bus
#define MPUREG_INT_ENABLE                               0x38
// bit definitions for MPUREG_INT_ENABLE
#       define BIT_RAW_RDY_EN                                   0x01
#       define BIT_DMP_INT_EN                                   0x02    // enabling this bit (DMP_INT_EN) also enables RAW_RDY_EN it seems
#       define BIT_UNKNOWN_INT_EN                               0x04
#       define BIT_I2C_MST_INT_EN                               0x08
#       define BIT_FIFO_OFLOW_EN                                0x10
#       define BIT_ZMOT_EN                                              0x20
#       define BIT_MOT_EN                                               0x40
#       define BIT_FF_EN                                                0x80
#define MPUREG_INT_STATUS                               0x3A
// bit definitions for MPUREG_INT_STATUS (same bit pattern as above because this register shows what interrupt actually fired)
#       define BIT_RAW_RDY_INT                                  0x01
#       define BIT_DMP_INT                                              0x02
#       define BIT_UNKNOWN_INT                                  0x04
#       define BIT_I2C_MST_INT                                  0x08
#       define BIT_FIFO_OFLOW_INT                               0x10
#       define BIT_ZMOT_INT                                             0x20
#       define BIT_MOT_INT                                              0x40
#       define BIT_FF_INT                                               0x80
#define MPUREG_ACCEL_XOUT_H                             0x3B
#define MPUREG_ACCEL_XOUT_L                             0x3C
#define MPUREG_ACCEL_YOUT_H                             0x3D
#define MPUREG_ACCEL_YOUT_L                             0x3E
#define MPUREG_ACCEL_ZOUT_H                             0x3F
#define MPUREG_ACCEL_ZOUT_L                             0x40
#define MPUREG_TEMP_OUT_H                               0x41
#define MPUREG_TEMP_OUT_L                               0x42
#define MPUREG_GYRO_XOUT_H                              0x43
#define MPUREG_GYRO_XOUT_L                              0x44
#define MPUREG_GYRO_YOUT_H                              0x45
#define MPUREG_GYRO_YOUT_L                              0x46
#define MPUREG_GYRO_ZOUT_H                              0x47
#define MPUREG_GYRO_ZOUT_L                              0x48
#define MPUREG_USER_CTRL                                0x6A
// bit definitions for MPUREG_USER_CTRL
#       define BIT_USER_CTRL_SIG_COND_RESET             0x01            // resets signal paths and results registers for all sensors (gyros, accel, temp)
#       define BIT_USER_CTRL_I2C_MST_RESET              0x02            // reset I2C Master (only applicable if I2C_MST_EN bit is set)
#       define BIT_USER_CTRL_FIFO_RESET                 0x04            // Reset (i.e. clear) FIFO buffer
#       define BIT_USER_CTRL_DMP_RESET                  0x08            // Reset DMP
#       define BIT_USER_CTRL_I2C_IF_DIS                 0x10            // Disable primary I2C interface and enable hal.spi->interface
#       define BIT_USER_CTRL_I2C_MST_EN                 0x20            // Enable MPU to act as the I2C Master to external slave sensors
#       define BIT_USER_CTRL_FIFO_EN                    0x40            // Enable FIFO operations
#       define BIT_USER_CTRL_DMP_EN                             0x80            // Enable DMP operations
#define MPUREG_PWR_MGMT_1                               0x6B
#       define BIT_PWR_MGMT_1_CLK_INTERNAL              0x00            // clock set to internal 8Mhz oscillator
#       define BIT_PWR_MGMT_1_CLK_XGYRO                 0x01            // PLL with X axis gyroscope reference
#       define BIT_PWR_MGMT_1_CLK_YGYRO                 0x02            // PLL with Y axis gyroscope reference
#       define BIT_PWR_MGMT_1_CLK_ZGYRO                 0x03            // PLL with Z axis gyroscope reference
#       define BIT_PWR_MGMT_1_CLK_EXT32KHZ              0x04            // PLL with external 32.768kHz reference
#       define BIT_PWR_MGMT_1_CLK_EXT19MHZ              0x05            // PLL with external 19.2MHz reference
#       define BIT_PWR_MGMT_1_CLK_STOP                  0x07            // Stops the clock and keeps the timing generator in reset
#       define BIT_PWR_MGMT_1_TEMP_DIS                  0x08            // disable temperature sensor
#       define BIT_PWR_MGMT_1_CYCLE                             0x20            // put sensor into cycle mode.  cycles between sleep mode and waking up to take a single sample of data from active sensors at a rate determined by LP_WAKE_CTRL
#       define BIT_PWR_MGMT_1_SLEEP                             0x40            // put sensor into low power sleep mode
#       define BIT_PWR_MGMT_1_DEVICE_RESET              0x80            // reset entire device
#define MPUREG_PWR_MGMT_2                               0x6C            // allows the user to configure the frequency of wake-ups in Accelerometer Only Low Power Mode
#define MPUREG_BANK_SEL                                 0x6D            // DMP bank selection register (used to indirectly access DMP registers)
#define MPUREG_MEM_START_ADDR                   0x6E            // DMP memory start address (used to indirectly write to dmp memory)
#define MPUREG_MEM_R_W                                  0x6F            // DMP related register
#define MPUREG_DMP_CFG_1                                0x70            // DMP related register
#define MPUREG_DMP_CFG_2                                0x71            // DMP related register
#define MPUREG_FIFO_COUNTH                              0x72
#define MPUREG_FIFO_COUNTL                              0x73
#define MPUREG_FIFO_R_W                                 0x74
#define MPUREG_WHOAMI                                   0x75
#define MPUREG_WHOAMI_MPU9250                           0x71
#define MPUREG_WHOAMI_MPU9255                           0x73

/* bit definitions for MPUREG_MST_CTRL */
#define MPUREG_I2C_MST_CTRL                             0x24
#        define I2C_MST_P_NSR                           0x10
#        define I2C_SLV0_EN                             0x80
#        define I2C_MST_CLOCK_400KHZ                    0x0D
#        define I2C_MST_CLOCK_258KHZ                    0x08
#define MPUREG_I2C_SLV4_CTRL                            0x34
#define MPUREG_I2C_MST_DELAY_CTRL                       0x67
#        define I2C_SLV0_DLY_EN                         0x01
#        define I2C_SLV1_DLY_EN                         0x02
#        define I2C_SLV2_DLY_EN                         0x04
#        define I2C_SLV3_DLY_EN                         0x08
#define READ_FLAG                                       0x80
#define MPUREG_I2C_SLV0_ADDR                            0x25
#define MPUREG_EXT_SENS_DATA_00                         0x49
#define MPUREG_I2C_SLV0_DO                              0x63

// Configuration bits MPU 3000, MPU 6000 and MPU9250
#define BITS_DLPF_CFG_256HZ_NOLPF2              0x00
#define BITS_DLPF_CFG_188HZ                             0x01
#define BITS_DLPF_CFG_98HZ                              0x02
#define BITS_DLPF_CFG_42HZ                              0x03
#define BITS_DLPF_CFG_20HZ                              0x04
#define BITS_DLPF_CFG_10HZ                              0x05
#define BITS_DLPF_CFG_5HZ                               0x06
#define BITS_DLPF_CFG_2100HZ_NOLPF              0x07
#define BITS_DLPF_CFG_MASK                              0x07
#define BITS_DLPF_FCHOICE_B                             0x08

#define MPU9250_SAMPLE_SIZE 14
#define MPU9250_MAX_FIFO_SAMPLES 20
#define MAX_DATA_READ (MPU9250_MAX_FIFO_SAMPLES * MPU9250_SAMPLE_SIZE)

#define int16_val(v, idx) ((int16_t)(((uint16_t)v[2*idx] << 8) | v[2*idx+1]))
#define uint16_val(v, idx)(((uint16_t)v[2*idx] << 8) | v[2*idx+1])

/*
 *  PS-MPU-9250A-00.pdf, page 8, lists LSB sensitivity of
 *  gyro as 16.4 LSB/DPS at scale factor of +/- 2000dps (FS_SEL==3)
 */
static const float GYRO_SCALE = 0.0174532f / 16.4f;

/*
 *  PS-MPU-9250A-00.pdf, page 9, lists LSB sensitivity of
 *  accel as 4096 LSB/mg at scale factor of +/- 8g (AFS_SEL==2)
 *
 *  See note below about accel scaling of engineering sample MPUXk
 *  variants however
 */

AP_InertialSensor_MPU9250::AP_InertialSensor_MPU9250(AP_InertialSensor &imu,
                                                     AP_HAL::OwnPtr<AP_HAL::Device> dev,
                                                     bool fast_sampling,
                                                     enum Rotation rotation)
    : AP_InertialSensor_Backend(imu)
    , _temp_filter(1000, 1)
    , _rotation(rotation)
    , _dev(std::move(dev))
    , _fast_sampling(fast_sampling)
{
}

AP_InertialSensor_MPU9250::~AP_InertialSensor_MPU9250()
{
    delete _auxiliary_bus;
}

AP_InertialSensor_Backend *AP_InertialSensor_MPU9250::probe(AP_InertialSensor &imu,
                                                            AP_HAL::OwnPtr<AP_HAL::I2CDevice> dev,
                                                            enum Rotation rotation)
{
    if (!dev) {
        return nullptr;
    }
    AP_InertialSensor_MPU9250 *sensor =
        new AP_InertialSensor_MPU9250(imu, std::move(dev), false, rotation);
    if (!sensor || !sensor->_init()) {
        delete sensor;
        return nullptr;
    }
    sensor->_id = HAL_INS_MPU9250_I2C;

    return sensor;
}


AP_InertialSensor_Backend *AP_InertialSensor_MPU9250::probe(AP_InertialSensor &imu,
                                                            AP_HAL::OwnPtr<AP_HAL::SPIDevice> dev,
                                                            bool fast_sampling,
                                                            enum Rotation rotation)
{
    if (!dev) {
        return nullptr;
    }
    AP_InertialSensor_MPU9250 *sensor;

    dev->set_read_flag(0x80);

    sensor = new AP_InertialSensor_MPU9250(imu, std::move(dev), fast_sampling, rotation);
    if (!sensor || !sensor->_init()) {
        delete sensor;
        return nullptr;
    }
    sensor->_id = HAL_INS_MPU9250_SPI;

    return sensor;
}

bool AP_InertialSensor_MPU9250::_init()
{
    bool success = _hardware_init();

#if MPU9250_DEBUG
    _dump_registers();
#endif

    return success;
}

void AP_InertialSensor_MPU9250::_fifo_reset()
{
    uint8_t user_ctrl = _master_i2c_enable?BIT_USER_CTRL_I2C_MST_EN:0;
    _register_write(MPUREG_USER_CTRL, user_ctrl);
    _register_write(MPUREG_USER_CTRL, user_ctrl | BIT_USER_CTRL_FIFO_RESET);
    _register_write(MPUREG_USER_CTRL, user_ctrl | BIT_USER_CTRL_FIFO_EN);
}

void AP_InertialSensor_MPU9250::_fifo_enable()
{
    _register_write(MPUREG_FIFO_EN, BIT_XG_FIFO_EN | BIT_YG_FIFO_EN |
                    BIT_ZG_FIFO_EN | BIT_ACCEL_FIFO_EN | BIT_TEMP_FIFO_EN);
    _fifo_reset();
    hal.scheduler->delay(1);
}

bool AP_InertialSensor_MPU9250::_has_auxiliary_bus()
{
    return _dev->bus_type() != AP_HAL::Device::BUS_TYPE_I2C;
}

void AP_InertialSensor_MPU9250::start()
{
    if (!_dev->get_semaphore()->take(100)) {
        AP_HAL::panic("MPU92500: Unable to get semaphore");
    }

    // initially run the bus at low speed
    _dev->set_speed(AP_HAL::Device::SPEED_LOW);

    // only used for wake-up in accelerometer only low power mode
    _register_write(MPUREG_PWR_MGMT_2, 0x00);
    hal.scheduler->delay(1);

    // always use FIFO
    _fifo_enable();

    if (_fast_sampling) {
        // setup for fast sampling
        _register_write(MPUREG_CONFIG, BITS_DLPF_CFG_256HZ_NOLPF2);
    } else {
        _register_write(MPUREG_CONFIG, BITS_DLPF_CFG_188HZ);
    }
    
    // set sample rate to 1kHz, and use the 2 pole filter to give the
    // desired rate
    _register_write(MPUREG_SMPLRT_DIV, 0);
    hal.scheduler->delay(1);

    // Gyro scale 2000º/s
    _register_write(MPUREG_GYRO_CONFIG, BITS_GYRO_FS_2000DPS);
    hal.scheduler->delay(1);

    // RM-MPU-9250A-00.pdf, pg. 15, select accel full scale 16g
    _register_write(MPUREG_ACCEL_CONFIG,3<<3);

    if (_fast_sampling) {
        // setup ACCEL_FCHOICE for 4kHz sampling
        _register_write(MPUREG_ACCEL_CONFIG2, 0x08);
    } else {
        _register_write(MPUREG_ACCEL_CONFIG2, 0x00);
    }
    
    // configure interrupt to fire when new data arrives
    _register_write(MPUREG_INT_ENABLE, BIT_RAW_RDY_EN);

    // clear interrupt on any read, and hold the data ready pin high
    // until we clear the interrupt
    uint8_t value = _register_read(MPUREG_INT_PIN_CFG);
    value |= BIT_INT_RD_CLEAR | BIT_LATCH_INT_EN;
    _register_write(MPUREG_INT_PIN_CFG, value);

    // now that we have initialised, we set the bus speed to high
    _dev->set_speed(AP_HAL::Device::SPEED_HIGH);

    _dev->get_semaphore()->give();

    // grab the used instances
    _gyro_instance = _imu.register_gyro(1000, _dev->get_bus_id_devtype(DEVTYPE_GYR_MPU9250));
    _accel_instance = _imu.register_accel(1000, _dev->get_bus_id_devtype(DEVTYPE_ACC_MPU9250));

    set_gyro_orientation(_gyro_instance, _rotation);
    set_accel_orientation(_accel_instance, _rotation);

    // allocate fifo buffer
    _fifo_buffer = new uint8_t[MAX_DATA_READ];
    if (_fifo_buffer == nullptr) {
        AP_HAL::panic("MPU9250: Unable to allocate FIFO buffer");
    }
    
    // start the timer process to read samples
    _dev->register_periodic_callback(1000, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_MPU9250::_read_sample, bool));
}

/*
  update the accel and gyro vectors
 */
bool AP_InertialSensor_MPU9250::update()
{
    update_gyro(_gyro_instance);
    update_accel(_accel_instance);

    _publish_temperature(_accel_instance, _temp_filtered);
    
    return true;
}

AuxiliaryBus *AP_InertialSensor_MPU9250::get_auxiliary_bus()
{
    if (_auxiliary_bus) {
        return _auxiliary_bus;
    }

    if (_has_auxiliary_bus()) {
        _auxiliary_bus = new AP_MPU9250_AuxiliaryBus(*this, _dev->get_bus_id());
    }

    return _auxiliary_bus;
}

/*
 * Return true if the MPU9250 has new data available for reading.
 */
bool AP_InertialSensor_MPU9250::_data_ready()
{
    uint8_t int_status = _register_read(MPUREG_INT_STATUS);
    return _data_ready(int_status);
}

bool AP_InertialSensor_MPU9250::_data_ready(uint8_t int_status)
{
    return (int_status & BIT_RAW_RDY_INT) != 0;
}


void AP_InertialSensor_MPU9250::_accumulate(uint8_t *samples, uint8_t n_samples)
{
    for (uint8_t i = 0; i < n_samples; i++) {
        uint8_t *data = samples + MPU9250_SAMPLE_SIZE * i;
        Vector3f accel, gyro;

        accel = Vector3f(int16_val(data, 1),
                         int16_val(data, 0),
                         -int16_val(data, 2));
        accel *= MPU9250_ACCEL_SCALE_1G;

        float temp = int16_val(data, 3);
        temp = temp/340 + 36.53;
        _last_temp = temp;
        
        gyro = Vector3f(int16_val(data, 5),
                        int16_val(data, 4),
                        -int16_val(data, 6));
        gyro *= GYRO_SCALE;

        _rotate_and_correct_accel(_accel_instance, accel);
        _rotate_and_correct_gyro(_gyro_instance, gyro);

        _notify_new_accel_raw_sample(_accel_instance, accel, AP_HAL::micros64());
        _notify_new_gyro_raw_sample(_gyro_instance, gyro);

        _temp_filtered = _temp_filter.apply(temp);
    }
}

void AP_InertialSensor_MPU9250::_accumulate_fast_sampling(uint8_t *samples, uint8_t n_samples)
{
    Vector3l asum, gsum;
    float tsum = 0;

    for (uint8_t i = 0; i < n_samples; i++) {
        uint8_t *data = samples + MPU9250_SAMPLE_SIZE * i;
        asum += Vector3l(int16_val(data, 1),
                          int16_val(data, 0),
                         -int16_val(data, 2));
        gsum += Vector3l(int16_val(data, 5),
                         int16_val(data, 4),
                         -int16_val(data, 6));

        float temp = int16_val(data, 3);
        temp = temp/340 + 36.53;
        tsum += temp;
        _last_temp = temp;
    }

    float ascale = MPU9250_ACCEL_SCALE_1G / n_samples;
    Vector3f accel(asum.x*ascale, asum.y*ascale, asum.z*ascale);

    float gscale = GYRO_SCALE / n_samples;
    Vector3f gyro(gsum.x*gscale, gsum.y*gscale, gsum.z*gscale);
    
    _rotate_and_correct_accel(_accel_instance, accel);
    _rotate_and_correct_gyro(_gyro_instance, gyro);
    
    _notify_new_accel_raw_sample(_accel_instance, accel, AP_HAL::micros64(), false);
    _notify_new_gyro_raw_sample(_gyro_instance, gyro);

    _temp_filtered = _temp_filter.apply(tsum / n_samples);
}


/*
 * check the FIFO integrity by cross-checking the temperature against
 * the last FIFO reading
 */
void AP_InertialSensor_MPU9250::_check_temperature(void)
{
    uint8_t rx[2];
    
    if (!_block_read(MPUREG_TEMP_OUT_H, rx, 2)) {
        return;
    }
    float temp = int16_val(rx, 0) / 340 + 36.53;

    if (fabsf(_last_temp - temp) > 2 && !is_zero(_last_temp)) {
        // a 2 degree change in one sample is a highly likely
        // sign of a FIFO alignment error
        printf("FIFO temperature reset: %.2f %.2f\n",
               (double)temp, (double)_last_temp);
        _last_temp = temp;
        _fifo_reset();
    }
}

/*
 * read from the data registers and update filtered data
 */
bool AP_InertialSensor_MPU9250::_read_sample()
{
    uint8_t n_samples;
    uint16_t bytes_read;
    uint8_t *rx = _fifo_buffer;

    if (!_block_read(MPUREG_FIFO_COUNTH, rx, 2)) {
        hal.console->printf("MPU9250: error in fifo read\n");
        return true;
    }

    bytes_read = uint16_val(rx, 0);
    n_samples = bytes_read / MPU9250_SAMPLE_SIZE;

    if (n_samples == 0) {
        /* Not enough data in FIFO */
        return true;
    }

    if (n_samples > MPU9250_MAX_FIFO_SAMPLES) {
        printf("bytes_read = %u, n_samples %u > %u, dropping samples\n",
               bytes_read, n_samples, MPU9250_MAX_FIFO_SAMPLES);

        /* Too many samples, do a FIFO RESET */
        _fifo_reset();
        return true;
    }

    if (!_block_read(MPUREG_FIFO_R_W, rx, n_samples * MPU9250_SAMPLE_SIZE)) {
        printf("MPU60x0: error in fifo read %u bytes\n",
               n_samples * MPU9250_SAMPLE_SIZE);
        return true;
    }

    if (_fast_sampling) {
        _accumulate_fast_sampling(rx, n_samples);
    } else {
        _accumulate_fast_sampling(rx, n_samples);
    }

    if (_temp_counter++ == 255) {
        // check FIFO integrity every 0.25s
        _check_temperature();
    }
    
    return true;
}

bool AP_InertialSensor_MPU9250::_block_read(uint8_t reg, uint8_t *buf,
                                            uint32_t size)
{
    return _dev->read_registers(reg, buf, size);
}

uint8_t AP_InertialSensor_MPU9250::_register_read(uint8_t reg)
{
    uint8_t val = 0;
    _dev->read_registers(reg, &val, 1);
    return val;
}

void AP_InertialSensor_MPU9250::_register_write(uint8_t reg, uint8_t val)
{
    _dev->write_register(reg, val);
}

bool AP_InertialSensor_MPU9250::_hardware_init(void)
{
    if (!_dev->get_semaphore()->take(100)) {
        AP_HAL::panic("MPU9250: Unable to get semaphore");
    }

    // initially run the bus at low speed
    _dev->set_speed(AP_HAL::Device::SPEED_LOW);

    uint8_t value = _register_read(MPUREG_WHOAMI);
    if (value != MPUREG_WHOAMI_MPU9250 && value != MPUREG_WHOAMI_MPU9255) {
        hal.console->printf("MPU9250: unexpected WHOAMI 0x%x\n", (unsigned)value);
        goto fail_whoami;
    }

    // Chip reset
    uint8_t tries;
    for (tries = 0; tries < 5; tries++) {
        uint8_t user_ctrl = _register_read(MPUREG_USER_CTRL);

        /* First disable the master I2C to avoid hanging the slaves on the
         * aulixiliar I2C bus - it will be enabled again if the AuxiliaryBus
         * is used */
        if (user_ctrl & BIT_USER_CTRL_I2C_MST_EN) {
            _register_write(MPUREG_USER_CTRL, user_ctrl & ~BIT_USER_CTRL_I2C_MST_EN);
            hal.scheduler->delay(10);
        }

        // reset device
        _register_write(MPUREG_PWR_MGMT_1, BIT_PWR_MGMT_1_DEVICE_RESET);
        hal.scheduler->delay(100);

        /* bus-dependent initialization */
        if (_dev->bus_type() == AP_HAL::Device::BUS_TYPE_SPI) {
            /* Disable I2C bus if SPI selected (Recommended in Datasheet to be
             * done just after the device is reset) */
            _register_write(MPUREG_USER_CTRL, BIT_USER_CTRL_I2C_IF_DIS);
        }

        // Wake up device and select GyroZ clock. Note that the
        // MPU9250 starts up in sleep mode, and it can take some time
        // for it to come out of sleep
        _register_write(MPUREG_PWR_MGMT_1, BIT_PWR_MGMT_1_CLK_ZGYRO);
        hal.scheduler->delay(5);

        // check it has woken up
        if (_register_read(MPUREG_PWR_MGMT_1) == BIT_PWR_MGMT_1_CLK_ZGYRO) {
            break;
        }

        hal.scheduler->delay(10);
        if (_data_ready()) {
            break;
        }

#if MPU9250_DEBUG
        _dump_registers();
#endif
    }
    if (tries == 5) {
        hal.console->println("Failed to boot MPU9250 5 times");
        goto fail_tries;
    }

    _dev->set_speed(AP_HAL::Device::SPEED_HIGH);
    _dev->get_semaphore()->give();

    return true;

fail_tries:
fail_whoami:
    _dev->get_semaphore()->give();
    _dev->set_speed(AP_HAL::Device::SPEED_HIGH);
    return false;
}

#if MPU9250_DEBUG
// dump all config registers - used for debug
void AP_InertialSensor_MPU9250::_dump_registers(AP_MPU9250_BusDriver *bus)
{
    hal.console->println("MPU9250 registers");
    for (uint8_t reg=0; reg<=126; reg++) {
        uint8_t v = _register_read(bus, reg);
        hal.console->printf("%02x:%02x ", (unsigned)reg, (unsigned)v);
        if ((reg - (MPUREG_PRODUCT_ID-1)) % 16 == 0) {
            hal.console->println();
        }
    }
    hal.console->println();
}
#endif

AP_MPU9250_AuxiliaryBusSlave::AP_MPU9250_AuxiliaryBusSlave(AuxiliaryBus &bus, uint8_t addr,
                                                           uint8_t instance)
    : AuxiliaryBusSlave(bus, addr, instance)
    , _mpu9250_addr(MPUREG_I2C_SLV0_ADDR + _instance * 3)
    , _mpu9250_reg(_mpu9250_addr + 1)
    , _mpu9250_ctrl(_mpu9250_addr + 2)
    , _mpu9250_do(MPUREG_I2C_SLV0_DO + _instance)
{
}

int AP_MPU9250_AuxiliaryBusSlave::_set_passthrough(uint8_t reg, uint8_t size,
                                                   uint8_t *out)
{
    auto &backend = AP_InertialSensor_MPU9250::from(_bus.get_backend());
    uint8_t addr;

    /* Ensure the slave read/write is disabled before changing the registers */
    backend._register_write(_mpu9250_ctrl, 0);

    if (out) {
        backend._register_write(_mpu9250_do, *out);
        addr = _addr;
    } else {
        addr = _addr | READ_FLAG;
    }

    backend._register_write(_mpu9250_addr, addr);
    backend._register_write(_mpu9250_reg, reg);
    backend._register_write(_mpu9250_ctrl, I2C_SLV0_EN | size);

    return 0;
}

int AP_MPU9250_AuxiliaryBusSlave::passthrough_read(uint8_t reg, uint8_t *buf,
                                                   uint8_t size)
{
    assert(buf);

    if (_registered) {
        hal.console->println("Error: can't passthrough when slave is already configured");
        return -1;
    }

    int r = _set_passthrough(reg, size);
    if (r < 0) {
        return r;
    }

    /* wait the value to be read from the slave and read it back */
    hal.scheduler->delay(10);

    auto &backend = AP_InertialSensor_MPU9250::from(_bus.get_backend());
    backend._block_read(MPUREG_EXT_SENS_DATA_00 + _ext_sens_data, buf, size);

    /* disable new reads */
    backend._register_write(_mpu9250_ctrl, 0);

    return size;
}

int AP_MPU9250_AuxiliaryBusSlave::passthrough_write(uint8_t reg, uint8_t val)
{
    if (_registered) {
        hal.console->println("Error: can't passthrough when slave is already configured");
        return -1;
    }

    int r = _set_passthrough(reg, 1, &val);
    if (r < 0) {
        return r;
    }

    /* wait the value to be written to the slave */
    hal.scheduler->delay(10);

    auto &backend = AP_InertialSensor_MPU9250::from(_bus.get_backend());

    /* disable new writes */
    backend._register_write(_mpu9250_ctrl, 0);

    return 1;
}

int AP_MPU9250_AuxiliaryBusSlave::read(uint8_t *buf)
{
    if (!_registered) {
        hal.console->println("Error: can't read before configuring slave");
        return -1;
    }

    auto &backend = AP_InertialSensor_MPU9250::from(_bus.get_backend());
    if (!backend._block_read(MPUREG_EXT_SENS_DATA_00 + _ext_sens_data, buf, _sample_size)) {
        return -1;
    }

    return _sample_size;
}

/* MPU9250 provides up to 5 slave devices, but the 5th is way too different to
 * configure and is seldom used */
AP_MPU9250_AuxiliaryBus::AP_MPU9250_AuxiliaryBus(AP_InertialSensor_MPU9250 &backend, uint32_t devid)
    : AuxiliaryBus(backend, 4, devid)
{
}

AP_HAL::Semaphore *AP_MPU9250_AuxiliaryBus::get_semaphore()
{
    return AP_InertialSensor_MPU9250::from(_ins_backend)._dev->get_semaphore();
}

AuxiliaryBusSlave *AP_MPU9250_AuxiliaryBus::_instantiate_slave(uint8_t addr, uint8_t instance)
{
    /* Enable slaves on MPU9250 if this is the first time */
    if (_ext_sens_data == 0)
        _configure_slaves();

    return new AP_MPU9250_AuxiliaryBusSlave(*this, addr, instance);
}

void AP_MPU9250_AuxiliaryBus::_configure_slaves()
{
    auto &backend = AP_InertialSensor_MPU9250::from(_ins_backend);

    /* Enable the I2C master to slaves on the auxiliary I2C bus*/
    uint8_t user_ctrl = backend._register_read(MPUREG_USER_CTRL);
    backend._register_write(MPUREG_USER_CTRL, user_ctrl | BIT_USER_CTRL_I2C_MST_EN);

    backend._master_i2c_enable = true;

    /* stop condition between reads; clock at 400kHz */
    backend._register_write(MPUREG_I2C_MST_CTRL,
                            I2C_MST_CLOCK_400KHZ | I2C_MST_P_NSR);

    /* Hard-code divider for internal sample rate, 1 kHz, resulting in a
     * sample rate of 100Hz */
    backend._register_write(MPUREG_I2C_SLV4_CTRL, 9);

    /* All slaves are subject to the sample rate */
    backend._register_write(MPUREG_I2C_MST_DELAY_CTRL,
                            I2C_SLV0_DLY_EN | I2C_SLV1_DLY_EN |
                            I2C_SLV2_DLY_EN | I2C_SLV3_DLY_EN);
}

int AP_MPU9250_AuxiliaryBus::_configure_periodic_read(AuxiliaryBusSlave *slave,
                                                      uint8_t reg, uint8_t size)
{
    if (_ext_sens_data + size > MAX_EXT_SENS_DATA) {
        return -1;
    }

    AP_MPU9250_AuxiliaryBusSlave *mpu_slave =
        static_cast<AP_MPU9250_AuxiliaryBusSlave*>(slave);
    mpu_slave->_set_passthrough(reg, size);
    mpu_slave->_ext_sens_data = _ext_sens_data;
    _ext_sens_data += size;

    return 0;
}