ardupilot/libraries/AP_AHRS/AP_AHRS_MPU6000.h

#ifndef AP_AHRS_MPU6000_H
#define AP_AHRS_MPU6000_H
/*
 *  DCM based AHRS (Attitude Heading Reference System) interface for
 *  ArduPilot
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 */

#define GYRO_BIAS_FROM_GRAVITY_RATE 4  // Rate of the gyro bias from gravity correction (200Hz/4) => 50Hz
#define HEADING_UNKNOWN -9999             // Initial value to detect that compass correction is not initialized

// max rate of gyro drift in gyro_LSB_units/s (16.4LSB = 1deg/s)
static const float _MPU6000_gyro_drift_rate = 0.5; // This correspond to 0.03 degrees/s/s;

class AP_AHRS_MPU6000 : public AP_AHRS
{
public:
    // Constructors
    AP_AHRS_MPU6000(AP_InertialSensor_MPU6000 *mpu6000, GPS *&gps) : AP_AHRS(mpu6000, gps), _mpu6000(mpu6000)
    {
        _dcm_matrix.identity();

        // these are experimentally derived from the simulator
        // with large drift levels
        _ki = 0.0087;
        _ki_yaw = 0.01;

        // dmp related variable initialisation
        _gyro_bias_from_gravity_gain = 0.008;
        _compass_bias_time = 0;
    }

    // initialisation routine to start MPU6000's dmp
    void init( AP_PeriodicProcess * scheduler = NULL );

    // return the smoothed gyro vector corrected for drift
    Vector3f        get_gyro(void) {
        return _ins->get_gyro();
    }
    Matrix3f        get_dcm_matrix(void) {
        return _dcm_matrix;
    }

    // return the current drift correction integrator value
    Vector3f        get_gyro_drift(void) {
        return _omega_I;
    }

    // Methods
    void            update(void);
    void            reset(bool recover_eulers = false);

    // push offsets down from IMU to INS (required so MPU6000 can perform it's own attitude estimation)
    void            push_offsets_to_ins();
    void            push_gains_to_dmp();

    // status reporting
    float           get_error_rp(void);
    float           get_error_yaw(void);

    // set_as_secondary - avoid running some steps twice (imu updates) if this is a secondary ahrs
    void            set_as_secondary(bool secondary) { _secondary_ahrs = secondary; }

private:
    float _ki;
    float _ki_yaw;
    AP_InertialSensor_MPU6000       *_mpu6000;

    // Methods
    void            drift_correction(float deltat);

    // Compass correction variables. TO-DO: move or replace?
    float           wrap_PI(float angle_in_radians);            // TO-DO: move this to standard AP_AHRS methods
    long _compass_bias_time;

    void            drift_correction_yaw(void);
    float           yaw_error_compass();
    void            euler_angles(void);

    Vector3f _accel_filtered;
    int16_t _accel_filtered_samples;
    float _gyro_bias[3];                                                        // bias_tracking
    float _gyro_bias_from_gravity_gain;                         // bias correction algorithm gain
    uint8_t _gyro_bias_from_gravity_counter;

    // primary representation of attitude
    Matrix3f _dcm_matrix;

    Vector3f _accel_vector;                     // current accel vector

    Vector3f _omega_I;                                  // Omega Integrator correction
    Vector3f _omega_I_sum;
    float _omega_I_sum_time;

    // state to support status reporting
    float _error_yaw_sum;
    uint16_t _error_yaw_count;
    float _error_yaw_last;

    bool _secondary_ahrs;
};

#endif // AP_AHRS_MPU6000_H