ardupilot/libraries/AP_InertialSensor/AP_InertialSensor.h

#pragma once

// Gyro and Accelerometer calibration criteria
#define AP_INERTIAL_SENSOR_ACCEL_TOT_MAX_OFFSET_CHANGE  4.0f
#define AP_INERTIAL_SENSOR_ACCEL_MAX_OFFSET             250.0f
#define AP_INERTIAL_SENSOR_ACCEL_VIBE_FLOOR_FILT_HZ     5.0f    // accel vibration floor filter hz
#define AP_INERTIAL_SENSOR_ACCEL_VIBE_FILT_HZ           2.0f    // accel vibration filter hz
#define AP_INERTIAL_SENSOR_ACCEL_PEAK_DETECT_TIMEOUT_MS 500     // peak-hold detector timeout

#include <AP_HAL/AP_HAL.h>

/**
   maximum number of INS instances available on this platform. If more
   than 1 then redundant sensors may be available
 */
#ifndef INS_MAX_INSTANCES
#define INS_MAX_INSTANCES 3
#endif
#define INS_MAX_BACKENDS  2*INS_MAX_INSTANCES
#define INS_MAX_NOTCHES 12
#ifndef INS_VIBRATION_CHECK_INSTANCES
  #if HAL_MEM_CLASS >= HAL_MEM_CLASS_300
    #define INS_VIBRATION_CHECK_INSTANCES INS_MAX_INSTANCES
  #else
    #define INS_VIBRATION_CHECK_INSTANCES 1
  #endif
#endif
#define XYZ_AXIS_COUNT    3
// The maximum we need to store is gyro-rate / loop-rate, worst case ArduCopter with BMI088 is 2000/400
#define INS_MAX_GYRO_WINDOW_SAMPLES 8

#define DEFAULT_IMU_LOG_BAT_MASK 0

#ifndef HAL_INS_TEMPERATURE_CAL_ENABLE
#define HAL_INS_TEMPERATURE_CAL_ENABLE !HAL_MINIMIZE_FEATURES && BOARD_FLASH_SIZE > 1024
#endif


#include <stdint.h>

#include <AP_AccelCal/AP_AccelCal.h>
#include <AP_HAL/utility/RingBuffer.h>
#include <AP_Math/AP_Math.h>
#include <AP_ExternalAHRS/AP_ExternalAHRS.h>
#include <Filter/LowPassFilter2p.h>
#include <Filter/LowPassFilter.h>
#include <Filter/HarmonicNotchFilter.h>
#include <AP_Math/polyfit.h>

#ifndef AP_SIM_INS_ENABLED
#define AP_SIM_INS_ENABLED (CONFIG_HAL_BOARD == HAL_BOARD_SITL)
#endif

class AP_InertialSensor_Backend;
class AuxiliaryBus;
class AP_AHRS;

/*
  forward declare AP_Logger class. We can't include logger.h
  because of mutual dependencies
 */
class AP_Logger;

/* AP_InertialSensor is an abstraction for gyro and accel measurements
 * which are correctly aligned to the body axes and scaled to SI units.
 *
 * Gauss-Newton accel calibration routines borrowed from Rolfe Schmidt
 * blog post describing the method: http://chionophilous.wordpress.com/2011/10/24/accelerometer-calibration-iv-1-implementing-gauss-newton-on-an-atmega/
 * original sketch available at http://rolfeschmidt.com/mathtools/skimetrics/adxl_gn_calibration.pde
 */
class AP_InertialSensor : AP_AccelCal_Client
{
    friend class AP_InertialSensor_Backend;

public:
    AP_InertialSensor();

    /* Do not allow copies */
    AP_InertialSensor(const AP_InertialSensor &other) = delete;
    AP_InertialSensor &operator=(const AP_InertialSensor&) = delete;

    static AP_InertialSensor *get_singleton();

    enum Gyro_Calibration_Timing {
        GYRO_CAL_NEVER = 0,
        GYRO_CAL_STARTUP_ONLY = 1
    };

    /// Perform startup initialisation.
    ///
    /// Called to initialise the state of the IMU.
    ///
    /// Gyros will be calibrated unless INS_GYRO_CAL is zero
    ///
    /// @param style	The initialisation startup style.
    ///
    void init(uint16_t sample_rate_hz);

    /// Register a new gyro/accel driver, allocating an instance
    /// number
    bool register_gyro(uint8_t &instance, uint16_t raw_sample_rate_hz, uint32_t id);
    bool register_accel(uint8_t &instance, uint16_t raw_sample_rate_hz, uint32_t id);

    // a function called by the main thread at the main loop rate:
    void periodic();

    bool calibrate_trim(Vector3f &trim_rad);

    /// calibrating - returns true if the gyros or accels are currently being calibrated
    bool calibrating() const;

    /// calibrating - returns true if a temperature calibration is running
    bool temperature_cal_running() const;
    
    /// Perform cold-start initialisation for just the gyros.
    ///
    /// @note This should not be called unless ::init has previously
    ///       been called, as ::init may perform other work
    ///
    void init_gyro(void);

    // get startup messages to output to the GCS
    bool get_output_banner(uint8_t instance_id, char* banner, uint8_t banner_len);

    /// Fetch the current gyro values
    ///
    /// @returns	vector of rotational rates in radians/sec
    ///
    const Vector3f     &get_gyro(uint8_t i) const { return _gyro[i]; }
    const Vector3f     &get_gyro(void) const { return get_gyro(_primary_gyro); }

    // set gyro offsets in radians/sec
    const Vector3f &get_gyro_offsets(uint8_t i) const { return _gyro_offset[i]; }
    const Vector3f &get_gyro_offsets(void) const { return get_gyro_offsets(_primary_gyro); }

    //get delta angle if available
    bool get_delta_angle(uint8_t i, Vector3f &delta_angle, float &delta_angle_dt) const;
    bool get_delta_angle(Vector3f &delta_angle, float &delta_angle_dt) const {
        return get_delta_angle(_primary_gyro, delta_angle, delta_angle_dt);
    }

    //get delta velocity if available
    bool get_delta_velocity(uint8_t i, Vector3f &delta_velocity, float &delta_velocity_dt) const;
    bool get_delta_velocity(Vector3f &delta_velocity, float &delta_velocity_dt) const {
        return get_delta_velocity(_primary_accel, delta_velocity, delta_velocity_dt);
    }

    /// Fetch the current accelerometer values
    ///
    /// @returns	vector of current accelerations in m/s/s
    ///
    const Vector3f     &get_accel(uint8_t i) const { return _accel[i]; }
    const Vector3f     &get_accel(void) const { return get_accel(_primary_accel); }

    uint32_t get_gyro_error_count(uint8_t i) const { return _gyro_error_count[i]; }
    uint32_t get_accel_error_count(uint8_t i) const { return _accel_error_count[i]; }

    // multi-device interface
    bool get_gyro_health(uint8_t instance) const { return (instance<_gyro_count) ? _gyro_healthy[instance] : false; }
    bool get_gyro_health(void) const { return get_gyro_health(_primary_gyro); }
    bool get_gyro_health_all(void) const;
    uint8_t get_gyro_count(void) const { return MIN(INS_MAX_INSTANCES, _accel_count); }
    bool gyro_calibrated_ok(uint8_t instance) const { return _gyro_cal_ok[instance]; }
    bool gyro_calibrated_ok_all() const;
    bool use_gyro(uint8_t instance) const;
    Gyro_Calibration_Timing gyro_calibration_timing();

    bool get_accel_health(uint8_t instance) const { return (instance<_accel_count) ? _accel_healthy[instance] : false; }
    bool get_accel_health(void) const { return get_accel_health(_primary_accel); }
    bool get_accel_health_all(void) const;
    uint8_t get_accel_count(void) const { return MIN(INS_MAX_INSTANCES, _accel_count); }
    bool accel_calibrated_ok_all() const;
    bool use_accel(uint8_t instance) const;

    // get observed sensor rates, including any internal sampling multiplier
    uint16_t get_gyro_rate_hz(uint8_t instance) const { return uint16_t(_gyro_raw_sample_rates[instance] * _gyro_over_sampling[instance]); }
    uint16_t get_accel_rate_hz(uint8_t instance) const { return uint16_t(_accel_raw_sample_rates[instance] * _accel_over_sampling[instance]); }

    // FFT support access
#if HAL_WITH_DSP
    const Vector3f     &get_raw_gyro(void) const { return _gyro_raw[_primary_gyro]; }
    FloatBuffer&  get_raw_gyro_window(uint8_t instance, uint8_t axis) { return _gyro_window[instance][axis]; }
    FloatBuffer&  get_raw_gyro_window(uint8_t axis) { return get_raw_gyro_window(_primary_gyro, axis); }
    uint16_t get_raw_gyro_rate_hz() const { return get_raw_gyro_rate_hz(_primary_gyro); }
    uint16_t get_raw_gyro_rate_hz(uint8_t instance) const { return _gyro_raw_sample_rates[_primary_gyro]; }
#endif
    bool set_gyro_window_size(uint16_t size);
    // get accel offsets in m/s/s
    const Vector3f &get_accel_offsets(uint8_t i) const { return _accel_offset[i]; }
    const Vector3f &get_accel_offsets(void) const { return get_accel_offsets(_primary_accel); }

    // get accel scale
    const Vector3f &get_accel_scale(uint8_t i) const { return _accel_scale[i]; }
    const Vector3f &get_accel_scale(void) const { return get_accel_scale(_primary_accel); }

    // return a 3D vector defining the position offset of the IMU accelerometer in metres relative to the body frame origin
    const Vector3f &get_imu_pos_offset(uint8_t instance) const {
        return _accel_pos[instance];
    }
    const Vector3f &get_imu_pos_offset(void) const {
        return _accel_pos[_primary_accel];
    }

    // return the temperature if supported. Zero is returned if no
    // temperature is available
    float get_temperature(uint8_t instance) const { return _temperature[instance]; }

    /* get_delta_time returns the time period in seconds
     * overwhich the sensor data was collected
     */
    float get_delta_time() const { return MIN(_delta_time, _loop_delta_t_max); }

    // return the maximum gyro drift rate in radians/s/s. This
    // depends on what gyro chips are being used
    float get_gyro_drift_rate(void) const { return ToRad(0.5f/60); }

    // update gyro and accel values from accumulated samples
    void update(void);

    // wait for a sample to be available
    void wait_for_sample(void);

    // class level parameters
    static const struct AP_Param::GroupInfo var_info[];

    // set overall board orientation
    void set_board_orientation(enum Rotation orientation, Matrix3f* custom_rotation = nullptr) {
        _board_orientation = orientation;
        _custom_rotation = custom_rotation;
    }

    // return the selected loop rate at which samples are made avilable
    uint16_t get_loop_rate_hz(void) const { return _loop_rate; }

    // return the main loop delta_t in seconds
    float get_loop_delta_t(void) const { return _loop_delta_t; }

    bool healthy(void) const { return get_gyro_health() && get_accel_health(); }

    uint8_t get_primary_accel(void) const { return _primary_accel; }
    uint8_t get_primary_gyro(void) const { return _primary_gyro; }

    // Update the harmonic notch frequency
    void update_harmonic_notch_freq_hz(float scaled_freq);
    // Update the harmonic notch frequencies
    void update_harmonic_notch_frequencies_hz(uint8_t num_freqs, const float scaled_freq[]);

    // get the gyro filter rate in Hz
    uint16_t get_gyro_filter_hz(void) const { return _gyro_filter_cutoff; }

    // get the accel filter rate in Hz
    uint16_t get_accel_filter_hz(void) const { return _accel_filter_cutoff; }

    // harmonic notch current center frequency
    float get_gyro_dynamic_notch_center_freq_hz(void) const { return _calculated_harmonic_notch_freq_hz[0]; }

    // number of dynamic harmonic notches
    uint8_t get_num_gyro_dynamic_notches(void) const { return _num_dynamic_harmonic_notches; }

    // set of harmonic notch current center frequencies
    const float* get_gyro_dynamic_notch_center_frequencies_hz(void) const { return _calculated_harmonic_notch_freq_hz; }

    // number of harmonic notch current center frequencies
    uint8_t get_num_gyro_dynamic_notch_center_frequencies(void) const { return _num_calculated_harmonic_notch_frequencies; }

    // harmonic notch reference center frequency
    float get_gyro_harmonic_notch_center_freq_hz(void) const { return _harmonic_notch_filter.center_freq_hz(); }

    // harmonic notch reference scale factor
    float get_gyro_harmonic_notch_reference(void) const { return _harmonic_notch_filter.reference(); }

    // harmonic notch tracking mode
    HarmonicNotchDynamicMode get_gyro_harmonic_notch_tracking_mode(void) const { return _harmonic_notch_filter.tracking_mode(); }

    // harmonic notch harmonics
    uint8_t get_gyro_harmonic_notch_harmonics(void) const { return _harmonic_notch_filter.harmonics(); }

    // harmonic notch options
    bool has_harmonic_option(HarmonicNotchFilterParams::Options option) {
        return _harmonic_notch_filter.hasOption(option);
    }

    // write out harmonic notch log messages
    void write_notch_log_messages() const;

    // indicate which bit in LOG_BITMASK indicates raw logging enabled
    void set_log_raw_bit(uint32_t log_raw_bit) { _log_raw_bit = log_raw_bit; }

    // Logging Functions
    void Write_IMU() const;
    void Write_Vibration() const;

    // calculate vibration levels and check for accelerometer clipping (called by a backends)
    void calc_vibration_and_clipping(uint8_t instance, const Vector3f &accel, float dt);

    // retrieve latest calculated vibration levels
    Vector3f get_vibration_levels() const { return get_vibration_levels(_primary_accel); }
    Vector3f get_vibration_levels(uint8_t instance) const;

    // retrieve and clear accelerometer clipping count
    uint32_t get_accel_clip_count(uint8_t instance) const;

    // check for vibration movement. True when all axis show nearly zero movement
    bool is_still();

    // return true if harmonic notch enabled
    bool gyro_harmonic_notch_enabled(void) const { return _harmonic_notch_filter.enabled(); }

    AuxiliaryBus *get_auxiliary_bus(int16_t backend_id) { return get_auxiliary_bus(backend_id, 0); }
    AuxiliaryBus *get_auxiliary_bus(int16_t backend_id, uint8_t instance);

    void detect_backends(void);

    // accel peak hold detector
    void set_accel_peak_hold(uint8_t instance, const Vector3f &accel);
    float get_accel_peak_hold_neg_x() const { return _peak_hold_state.accel_peak_hold_neg_x; }

    //Returns accel calibrator interface object pointer
    AP_AccelCal* get_acal() const { return _acal; }

    // Returns body fixed accelerometer level data averaged during accel calibration's first step
    bool get_fixed_mount_accel_cal_sample(uint8_t sample_num, Vector3f& ret) const;

    // Returns primary accelerometer level data averaged during accel calibration's first step
    bool get_primary_accel_cal_sample_avg(uint8_t sample_num, Vector3f& ret) const;

    // Returns newly calculated trim values if calculated
    bool get_new_trim(Vector3f &trim_rad);

    // initialise and register accel calibrator
    // called during the startup of accel cal
    void acal_init();

    // update accel calibrator
    void acal_update();

    // simple accel calibration
#if HAL_GCS_ENABLED
    MAV_RESULT simple_accel_cal();
#endif

    bool accel_cal_requires_reboot() const { return _accel_cal_requires_reboot; }

    // return time in microseconds of last update() call
    uint32_t get_last_update_usec(void) const { return _last_update_usec; }

    // for killing an IMU for testing purposes
    void kill_imu(uint8_t imu_idx, bool kill_it);

    enum IMU_SENSOR_TYPE {
        IMU_SENSOR_TYPE_ACCEL = 0,
        IMU_SENSOR_TYPE_GYRO = 1,
    };

    class BatchSampler {
    public:
        BatchSampler(const AP_InertialSensor &imu) :
            type(IMU_SENSOR_TYPE_ACCEL),
            _imu(imu) {
            AP_Param::setup_object_defaults(this, var_info);
        };

        void init();
        void sample(uint8_t instance, IMU_SENSOR_TYPE _type, uint64_t sample_us, const Vector3f &sample) __RAMFUNC__;

        // a function called by the main thread at the main loop rate:
        void periodic();

        bool doing_sensor_rate_logging() const { return _doing_sensor_rate_logging; }
        bool doing_post_filter_logging() const { return _doing_post_filter_logging; }

        // class level parameters
        static const struct AP_Param::GroupInfo var_info[];

        // Parameters
        AP_Int16 _required_count;
        AP_Int8 _sensor_mask;
        AP_Int8 _batch_options_mask;

        // Parameters controlling pushing data to AP_Logger:
        // Each DF message is ~ 108 bytes in size, so we use about 1kB/s of
        // logging bandwidth with a 100ms interval.  If we are taking
        // 1024 samples then we need to send 32 packets, so it will
        // take ~3 seconds to push a complete batch to the log.  If
        // you are running a on an FMU with three IMUs then you
        // will loop back around to the first sensor after about
        // twenty seconds.
        AP_Int16 samples_per_msg;
        AP_Int8 push_interval_ms;

        // end Parameters

    private:

        enum batch_opt_t {
            BATCH_OPT_SENSOR_RATE = (1<<0),
            BATCH_OPT_POST_FILTER = (1<<1),
        };

        void rotate_to_next_sensor();
        void update_doing_sensor_rate_logging();

        bool should_log(uint8_t instance, IMU_SENSOR_TYPE type) __RAMFUNC__;
        void push_data_to_log();

        // Logging functions
        bool Write_ISBH(const float sample_rate_hz) const;
        bool Write_ISBD() const;

        uint64_t measurement_started_us;

        bool initialised : 1;
        bool isbh_sent : 1;
        bool _doing_sensor_rate_logging : 1;
        bool _doing_post_filter_logging : 1;
        uint8_t instance : 3; // instance we are sending data for
        AP_InertialSensor::IMU_SENSOR_TYPE type : 1;
        uint16_t isb_seqnum;
        int16_t *data_x;
        int16_t *data_y;
        int16_t *data_z;
        uint16_t data_write_offset; // units: samples
        uint16_t data_read_offset; // units: samples
        uint32_t last_sent_ms;

        // all samples are multiplied by this
        uint16_t multiplier; // initialised as part of init()

        const AP_InertialSensor &_imu;
    };
    BatchSampler batchsampler{*this};

#if HAL_EXTERNAL_AHRS_ENABLED
    // handle external AHRS data
    void handle_external(const AP_ExternalAHRS::ins_data_message_t &pkt);
#endif

#if HAL_INS_TEMPERATURE_CAL_ENABLE
    /*
      get a string representation of parameters that should be made
      persistent across changes of firmware type
     */
    void get_persistent_params(ExpandingString &str) const;
#endif

    // force save of current calibration as valid
    void force_save_calibration(void);

private:
    // load backend drivers
    bool _add_backend(AP_InertialSensor_Backend *backend);
    void _start_backends();
    AP_InertialSensor_Backend *_find_backend(int16_t backend_id, uint8_t instance);

    // gyro initialisation
    void _init_gyro();

    // Calibration routines borrowed from Rolfe Schmidt
    // blog post describing the method: http://chionophilous.wordpress.com/2011/10/24/accelerometer-calibration-iv-1-implementing-gauss-newton-on-an-atmega/
    // original sketch available at http://rolfeschmidt.com/mathtools/skimetrics/adxl_gn_calibration.pde

    bool _calculate_trim(const Vector3f &accel_sample, Vector3f &trim_rad);

    // save gyro calibration values to eeprom
    void _save_gyro_calibration();

    // Logging function
    void Write_IMU_instance(const uint64_t time_us, const uint8_t imu_instance) const;
    
    // backend objects
    AP_InertialSensor_Backend *_backends[INS_MAX_BACKENDS];

    // number of gyros and accel drivers. Note that most backends
    // provide both accel and gyro data, so will increment both
    // counters on initialisation
    uint8_t _gyro_count;
    uint8_t _accel_count;
    uint8_t _backend_count;

    // the selected loop rate at which samples are made available
    uint16_t _loop_rate;
    float _loop_delta_t;
    float _loop_delta_t_max;

    // Most recent accelerometer reading
    Vector3f _accel[INS_MAX_INSTANCES];
    Vector3f _delta_velocity[INS_MAX_INSTANCES];
    float _delta_velocity_dt[INS_MAX_INSTANCES];
    bool _delta_velocity_valid[INS_MAX_INSTANCES];
    // delta velocity accumulator
    Vector3f _delta_velocity_acc[INS_MAX_INSTANCES];
    // time accumulator for delta velocity accumulator
    float _delta_velocity_acc_dt[INS_MAX_INSTANCES];

    // Low Pass filters for gyro and accel
    LowPassFilter2pVector3f _accel_filter[INS_MAX_INSTANCES];
    LowPassFilter2pVector3f _gyro_filter[INS_MAX_INSTANCES];
    Vector3f _accel_filtered[INS_MAX_INSTANCES];
    Vector3f _gyro_filtered[INS_MAX_INSTANCES];
#if HAL_WITH_DSP
    // Thread-safe public version of _last_raw_gyro
    Vector3f _gyro_raw[INS_MAX_INSTANCES];
    FloatBuffer _gyro_window[INS_MAX_INSTANCES][XYZ_AXIS_COUNT];
    uint16_t _gyro_window_size;
#endif
    bool _new_accel_data[INS_MAX_INSTANCES];
    bool _new_gyro_data[INS_MAX_INSTANCES];

    // optional notch filter on gyro
    HarmonicNotchFilterParams _notch_filter;
    HarmonicNotchFilterVector3f _gyro_notch_filter[INS_MAX_INSTANCES];

    // optional harmonic notch filter on gyro
    HarmonicNotchFilterParams _harmonic_notch_filter;
    HarmonicNotchFilterVector3f _gyro_harmonic_notch_filter[INS_MAX_INSTANCES];
    // number of independent notches in the filter
    uint8_t _num_dynamic_harmonic_notches;
    // the current center frequency for the notch
    float _calculated_harmonic_notch_freq_hz[INS_MAX_NOTCHES];
    uint8_t _num_calculated_harmonic_notch_frequencies;

    // Most recent gyro reading
    Vector3f _gyro[INS_MAX_INSTANCES];
    Vector3f _delta_angle[INS_MAX_INSTANCES];
    float _delta_angle_dt[INS_MAX_INSTANCES];
    bool _delta_angle_valid[INS_MAX_INSTANCES];
    // time accumulator for delta angle accumulator
    float _delta_angle_acc_dt[INS_MAX_INSTANCES];
    Vector3f _delta_angle_acc[INS_MAX_INSTANCES];
    Vector3f _last_delta_angle[INS_MAX_INSTANCES];
    Vector3f _last_raw_gyro[INS_MAX_INSTANCES];

    // bitmask indicating if a sensor is doing sensor-rate sampling:
    uint8_t _accel_sensor_rate_sampling_enabled;
    uint8_t _gyro_sensor_rate_sampling_enabled;

    // multipliers for data supplied via sensor-rate logging:
    uint16_t _accel_raw_sampling_multiplier[INS_MAX_INSTANCES];
    uint16_t _gyro_raw_sampling_multiplier[INS_MAX_INSTANCES];

    // IDs to uniquely identify each sensor: shall remain
    // the same across reboots
    AP_Int32 _accel_id[INS_MAX_INSTANCES];
    AP_Int32 _gyro_id[INS_MAX_INSTANCES];

    // accelerometer scaling and offsets
    AP_Vector3f _accel_scale[INS_MAX_INSTANCES];
    AP_Vector3f _accel_offset[INS_MAX_INSTANCES];
    AP_Vector3f _gyro_offset[INS_MAX_INSTANCES];

    // accelerometer position offset in body frame
    AP_Vector3f _accel_pos[INS_MAX_INSTANCES];

    // accelerometer max absolute offsets to be used for calibration
    float _accel_max_abs_offsets[INS_MAX_INSTANCES];

    // accelerometer and gyro raw sample rate in units of Hz
    float  _accel_raw_sample_rates[INS_MAX_INSTANCES];
    float  _gyro_raw_sample_rates[INS_MAX_INSTANCES];

    // how many sensors samples per notify to the backend
    uint8_t _accel_over_sampling[INS_MAX_INSTANCES];
    uint8_t _gyro_over_sampling[INS_MAX_INSTANCES];

    // last sample time in microseconds. Use for deltaT calculations
    // on non-FIFO sensors
    uint64_t _accel_last_sample_us[INS_MAX_INSTANCES];
    uint64_t _gyro_last_sample_us[INS_MAX_INSTANCES];

    // sample times for checking real sensor rate for FIFO sensors
    uint16_t _sample_accel_count[INS_MAX_INSTANCES];
    uint32_t _sample_accel_start_us[INS_MAX_INSTANCES];
    uint16_t _sample_gyro_count[INS_MAX_INSTANCES];
    uint32_t _sample_gyro_start_us[INS_MAX_INSTANCES];
    
    // temperatures for an instance if available
    float _temperature[INS_MAX_INSTANCES];

    // filtering frequency (0 means default)
    AP_Int16    _accel_filter_cutoff;
    AP_Int16    _gyro_filter_cutoff;
    AP_Int8     _gyro_cal_timing;

    // use for attitude, velocity, position estimates
    AP_Int8     _use[INS_MAX_INSTANCES];

    // control enable of fast sampling
    AP_Int8     _fast_sampling_mask;

    // control enable of fast sampling
    AP_Int8     _fast_sampling_rate;

    // control enable of detected sensors
    AP_Int8     _enable_mask;
    
    // board orientation from AHRS
    enum Rotation _board_orientation;
    Matrix3f* _custom_rotation;

    // per-sensor orientation to allow for board type defaults at runtime
    enum Rotation _gyro_orientation[INS_MAX_INSTANCES];
    enum Rotation _accel_orientation[INS_MAX_INSTANCES];

    // calibrated_ok/id_ok flags
    bool _gyro_cal_ok[INS_MAX_INSTANCES];
    bool _accel_id_ok[INS_MAX_INSTANCES];

    // primary accel and gyro
    uint8_t _primary_gyro;
    uint8_t _primary_accel;

    // mask of accels and gyros which we will be actively using
    // and this should wait for in wait_for_sample()
    uint8_t _gyro_wait_mask;
    uint8_t _accel_wait_mask;

    // bitmask bit which indicates if we should log raw accel and gyro data
    uint32_t _log_raw_bit;

    // has wait_for_sample() found a sample?
    bool _have_sample:1;

    bool _backends_detected:1;

    // are gyros or accels currently being calibrated
    bool _calibrating_accel;
    bool _calibrating_gyro;

    // the delta time in seconds for the last sample
    float _delta_time;

    // last time a wait_for_sample() returned a sample
    uint32_t _last_sample_usec;

    // target time for next wait_for_sample() return
    uint32_t _next_sample_usec;

    // time between samples in microseconds
    uint32_t _sample_period_usec;

    // last time update() completed
    uint32_t _last_update_usec;

    // health of gyros and accels
    bool _gyro_healthy[INS_MAX_INSTANCES];
    bool _accel_healthy[INS_MAX_INSTANCES];

    uint32_t _accel_error_count[INS_MAX_INSTANCES];
    uint32_t _gyro_error_count[INS_MAX_INSTANCES];

    // vibration and clipping
    uint32_t _accel_clip_count[INS_MAX_INSTANCES];
    LowPassFilterVector3f _accel_vibe_floor_filter[INS_VIBRATION_CHECK_INSTANCES];
    LowPassFilterVector3f _accel_vibe_filter[INS_VIBRATION_CHECK_INSTANCES];

    // peak hold detector state for primary accel
    struct PeakHoldState {
        float accel_peak_hold_neg_x;
        uint32_t accel_peak_hold_neg_x_age;
    } _peak_hold_state;

    // threshold for detecting stillness
    AP_Float _still_threshold;

    // Trim options
    AP_Int8 _acc_body_aligned;
    AP_Int8 _trim_option;

    static AP_InertialSensor *_singleton;
    AP_AccelCal* _acal;

    AccelCalibrator *_accel_calibrator;

    //save accelerometer bias and scale factors
    void _acal_save_calibrations() override;
    void _acal_event_failure() override;

    // Returns AccelCalibrator objects pointer for specified acceleromter
    AccelCalibrator* _acal_get_calibrator(uint8_t i) override { return i<get_accel_count()?&(_accel_calibrator[i]):nullptr; }

    Vector3f _trim_rad;
    bool _new_trim;

    bool _accel_cal_requires_reboot;

    // sensor error count at startup (used to ignore errors within 2 seconds of startup)
    uint32_t _accel_startup_error_count[INS_MAX_INSTANCES];
    uint32_t _gyro_startup_error_count[INS_MAX_INSTANCES];
    bool _startup_error_counts_set;
    uint32_t _startup_ms;

    uint8_t imu_kill_mask;

#if HAL_INS_TEMPERATURE_CAL_ENABLE
public:
    // TCal class is public for use by SITL
    class TCal {
    public:
        static const struct AP_Param::GroupInfo var_info[];
        void correct_accel(float temperature, float cal_temp, Vector3f &accel) const;
        void correct_gyro(float temperature, float cal_temp, Vector3f &accel) const;
        void sitl_apply_accel(float temperature, Vector3f &accel) const;
        void sitl_apply_gyro(float temperature, Vector3f &accel) const;

        void update_accel_learning(const Vector3f &accel);
        void update_gyro_learning(const Vector3f &accel);

        enum class Enable : uint8_t {
            Disabled = 0,
            Enabled = 1,
            LearnCalibration = 2,
        };

        // add samples for learning
        void update_accel_learning(const Vector3f &gyro, float temperature);
        void update_gyro_learning(const Vector3f &accel, float temperature);
        
        // class for online learning of calibration
        class Learn {
        public:
            Learn(TCal &_tcal, float _start_temp);

            // state for accel/gyro (accel first)
            struct LearnState {
                float last_temp;
                uint32_t last_sample_ms;
                Vector3f sum;
                uint32_t sum_count;
                LowPassFilter2p<float> temp_filter;
                // double precision is needed for good results when we
                // span a wide range of temperatures
                PolyFit<4, double, Vector3f> pfit;
            } state[2];

            void add_sample(const Vector3f &sample, float temperature, LearnState &state);
            void finish_calibration(float temperature);
            bool save_calibration(float temperature);
            void reset(float temperature);
            float start_temp;
            float start_tmax;
            uint32_t last_save_ms;

            TCal &tcal;
            uint8_t instance(void) const {
                return tcal.instance();
            }
            Vector3f accel_start;
        };

        AP_Enum<Enable> enable;

        // get persistent params for this instance
        void get_persistent_params(ExpandingString &str) const;

    private:
        AP_Float temp_max;
        AP_Float temp_min;
        AP_Vector3f accel_coeff[3];
        AP_Vector3f gyro_coeff[3];
        Vector3f accel_tref;
        Vector3f gyro_tref;
        Learn *learn;

        void correct_sensor(float temperature, float cal_temp, const AP_Vector3f coeff[3], Vector3f &v) const;
        Vector3f polynomial_eval(float temperature, const AP_Vector3f coeff[3]) const;

        // get instance number
        uint8_t instance(void) const;
    };

    // instance number for logging
    uint8_t tcal_instance(const TCal &tc) const {
        return &tc - &tcal[0];
    }
private:
    TCal tcal[INS_MAX_INSTANCES];

    enum class TCalOptions : uint8_t {
        PERSIST_TEMP_CAL = (1U<<0),
        PERSIST_ACCEL_CAL = (1U<<1),
    };

    // temperature that last calibration was run at
    AP_Float caltemp_accel[INS_MAX_INSTANCES];
    AP_Float caltemp_gyro[INS_MAX_INSTANCES];
    AP_Int32 tcal_options;
    bool tcal_learning;
#endif
};

namespace AP {
    AP_InertialSensor &ins();
};