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>

#define debug(fmt, args ...)  do {printf("MPU9250: " fmt "\n", ## args); } while(0)

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_CONFIG_FIFO_MODE_STOP                    0x40
#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 MPU_SAMPLE_SIZE 14
#define MPU_FIFO_DOWNSAMPLE_COUNT 8
#define MPU_FIFO_BUFFER_SIZE 16

#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,
                                                     enum Rotation rotation)
    : AP_InertialSensor_Backend(imu)
    , _temp_filter(1000, 1)
    , _rotation(rotation)
    , _dev(std::move(dev))
{
}

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), 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,
                                                            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), 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();
    return success;
}

void AP_InertialSensor_MPU9250::_fifo_reset()
{
    uint8_t user_ctrl = _last_stat_user_ctrl;
    user_ctrl &= ~(BIT_USER_CTRL_FIFO_RESET | BIT_USER_CTRL_FIFO_EN);
    _dev->set_speed(AP_HAL::Device::SPEED_LOW);
    _register_write(MPUREG_FIFO_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);
    _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, true);
    hal.scheduler->delay_microseconds(1);
    _dev->set_speed(AP_HAL::Device::SPEED_HIGH);
    _last_stat_user_ctrl = user_ctrl | BIT_USER_CTRL_FIFO_EN;
}

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(0)) {
        return;
    }

    // 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_reset();

    // 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));

    if (enable_fast_sampling(_accel_instance) && _dev->bus_type() == AP_HAL::Device::BUS_TYPE_SPI) {
        _fast_sampling = true;
        hal.console->printf("MPU9250: enabled fast sampling\n");
    }
    
    if (_fast_sampling) {
        // setup for fast sampling
        _register_write(MPUREG_CONFIG, BITS_DLPF_CFG_256HZ_NOLPF2 | MPUREG_CONFIG_FIFO_MODE_STOP, true);
    } else {
        _register_write(MPUREG_CONFIG, BITS_DLPF_CFG_188HZ | MPUREG_CONFIG_FIFO_MODE_STOP, true);
    }
    
    // set sample rate to 1kHz, and use the 2 pole filter to give the
    // desired rate
    _register_write(MPUREG_SMPLRT_DIV, 0, true);
    hal.scheduler->delay(1);

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

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

    if (_fast_sampling) {
        // setup ACCEL_FCHOICE for 4kHz sampling
        _register_write(MPUREG_ACCEL_CONFIG2, 0x08, true);
    } else {
        _register_write(MPUREG_ACCEL_CONFIG2, 0x00, true);
    }
    
    // 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();

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

    // allocate fifo buffer
    _fifo_buffer = (uint8_t *)hal.util->dma_allocate(MPU_FIFO_BUFFER_SIZE * MPU_SAMPLE_SIZE);
    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;
}

/*
  accumulate new samples
 */
void AP_InertialSensor_MPU9250::accumulate()
{
    // nothing to do
}


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;
}


bool AP_InertialSensor_MPU9250::_accumulate(uint8_t *samples, uint8_t n_samples, int16_t raw_temp)
{
    for (uint8_t i = 0; i < n_samples; i++) {
        const uint8_t *data = samples + MPU_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;

        int16_t t2 = int16_val(data, 3);
        if (abs(t2 - raw_temp) > 400) {
            debug("temp reset %d %d %d", raw_temp, t2, raw_temp-t2);
            _fifo_reset();
            return false;
        }
        float temp = t2/340 + 36.53;
        
        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);
    }
    return true;
}

/*
  when doing fast sampling the sensor gives us 8k samples/second. Every 2nd accel sample is a duplicate.

  To filter this we first apply a 1p low pass filter at 188Hz, then we
  average over 8 samples to bring the data rate down to 1kHz. This
  gives very good aliasing rejection at frequencies well above what
  can be handled with 1kHz sample rates.
 */
bool AP_InertialSensor_MPU9250::_accumulate_fast_sampling(uint8_t *samples, uint8_t n_samples, int16_t raw_temp)
{
    int32_t tsum = 0;
    const int32_t clip_limit = AP_INERTIAL_SENSOR_ACCEL_CLIP_THRESH_MSS / MPU9250_ACCEL_SCALE_1G;
    bool clipped = false;
    bool ret = true;
    
    for (uint8_t i = 0; i < n_samples; i++) {
        const uint8_t *data = samples + MPU_SAMPLE_SIZE * i;

        // use temperatue to detect FIFO corruption
        int16_t t2 = int16_val(data, 3);
        if (abs(t2 - raw_temp) > 400) {
            debug("temp reset %d %d %d", raw_temp, t2, raw_temp - t2);
            _fifo_reset();
            ret = false;
            break;
        }
        tsum += t2;

        if ((_accum.count & 1) == 0) {
            // accels are at 4kHz not 8kHz
            Vector3f a(int16_val(data, 1),
                       int16_val(data, 0),
                       -int16_val(data, 2));
            if (fabsf(a.x) > clip_limit ||
                fabsf(a.y) > clip_limit ||
                fabsf(a.z) > clip_limit) {
                clipped = true;
            }
            _accum.accel += _accum.accel_filter.apply(a);
        }
        Vector3f g(int16_val(data, 5),
                   int16_val(data, 4),
                   -int16_val(data, 6));

        _accum.gyro += _accum.gyro_filter.apply(g);
        _accum.count++;

        if (_accum.count == MPU_FIFO_DOWNSAMPLE_COUNT) {
            float ascale = MPU9250_ACCEL_SCALE_1G / (MPU_FIFO_DOWNSAMPLE_COUNT/2);
            _accum.accel *= ascale;
            
            float gscale = GYRO_SCALE / MPU_FIFO_DOWNSAMPLE_COUNT;
            _accum.gyro *= gscale;
            
            _rotate_and_correct_accel(_accel_instance, _accum.accel);
            _rotate_and_correct_gyro(_gyro_instance, _accum.gyro);
            
            _notify_new_accel_raw_sample(_accel_instance, _accum.accel, AP_HAL::micros64(), false);
            _notify_new_gyro_raw_sample(_gyro_instance, _accum.gyro);
            
            _accum.accel.zero();
            _accum.gyro.zero();
            _accum.count = 0;
        }
    }

    if (clipped) {
        increment_clip_count(_accel_instance);
    }

    if (ret) {
        float temp = (tsum/n_samples)/340.0 + 36.53;
        _temp_filtered = _temp_filter.apply(temp);
    }

    return ret;
}


/*
 * 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;
    int16_t raw_temp;
    uint8_t trx[2];
    bool need_reset = false;
    
    if (!_block_read(MPUREG_FIFO_COUNTH, rx, 2)) {
        goto check_registers;
    }

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

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

    /*
      fetch temperature in order to detect FIFO sync errors
     */
    if (!_block_read(MPUREG_TEMP_OUT_H, trx, 2)) {
        return true;
    }
    raw_temp = int16_val(trx, 0);

    /*
      testing has shown that if we have more than 32 samples in the
      FIFO then some of those samples will be corrupt. It always is
      the ones at the end of the FIFO, so clear those with a reset
      once we've read the first 24. Reading 24 gives us the normal
      number of samples for fast sampling at 400Hz
     */
    if (n_samples > 32) {
        need_reset = true;
        n_samples = 24;
    }
    
    while (n_samples > 0) {
        uint8_t n = MIN(MPU_FIFO_BUFFER_SIZE, n_samples);
        if (!_block_read(MPUREG_FIFO_R_W, rx, n * MPU_SAMPLE_SIZE)) {
            printf("MPU60x0: error in fifo read %u bytes\n", n * MPU_SAMPLE_SIZE);
            goto check_registers;
        }

        if (_fast_sampling) {
            if (!_accumulate_fast_sampling(rx, n, raw_temp)) {
                debug("stop at %u of %u", n_samples, bytes_read/MPU_SAMPLE_SIZE);
                break;
            }
        } else {
            if (!_accumulate(rx, n, raw_temp)) {
                break;
            }
        }
        n_samples -= n;
    }

    if (need_reset) {
        //debug("fifo reset %u", bytes_read/MPU_SAMPLE_SIZE);
        _fifo_reset();
    }
    
check_registers:
    if (_reg_check_counter++ == 10) {
        _reg_check_counter = 0;
        // check next register value for correctness
        if (!_dev->check_next_register()) {
            _inc_gyro_error_count(_gyro_instance);
            _inc_accel_error_count(_accel_instance);
        }
    }
    
    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, bool checked)
{
    _dev->write_register(reg, val, checked);
}

bool AP_InertialSensor_MPU9250::_hardware_init(void)
{
    if (!_dev->get_semaphore()->take(0)) {
        return false;
    }

    // setup for register checking
    _dev->setup_checked_registers(6);

    // 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++) {
        _last_stat_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 (_last_stat_user_ctrl & BIT_USER_CTRL_I2C_MST_EN) {
            _last_stat_user_ctrl &= ~BIT_USER_CTRL_I2C_MST_EN;
            _register_write(MPUREG_USER_CTRL, _last_stat_user_ctrl);
            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) */
            _last_stat_user_ctrl |= BIT_USER_CTRL_I2C_IF_DIS;
            _register_write(MPUREG_USER_CTRL, _last_stat_user_ctrl);
        }

        // 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 (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;
}

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*/
    if (!(backend._last_stat_user_ctrl & BIT_USER_CTRL_I2C_MST_EN)) {
        backend._last_stat_user_ctrl |= BIT_USER_CTRL_I2C_MST_EN;
        backend._register_write(MPUREG_USER_CTRL, backend._last_stat_user_ctrl);
    }

    /* 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;
}