AP_AHRS_Backend.h

#pragma once

/*
   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/>.
 */

/*
 *  AHRS (Attitude Heading Reference System) interface for ArduPilot
 *
 */

#include <AP_Math/AP_Math.h>
#include <inttypes.h>
#include <AP_Airspeed/AP_Airspeed.h>
#include <AP_InertialSensor/AP_InertialSensor.h>
#include <AP_Common/Location.h>
#include <AP_NavEKF/AP_NavEKF_Source.h>

#define AP_AHRS_TRIM_LIMIT 10.0f        // maximum trim angle in degrees
#define AP_AHRS_RP_P_MIN   0.05f        // minimum value for AHRS_RP_P parameter
#define AP_AHRS_YAW_P_MIN  0.05f        // minimum value for AHRS_YAW_P parameter

enum class GPSUse : uint8_t {
    Disable = 0,
    Enable  = 1,
    EnableWithHeight = 2,
};

class AP_AHRS_Backend
{
public:

    // Constructor
    AP_AHRS_Backend() {}

    // empty virtual destructor
    virtual ~AP_AHRS_Backend() {}

    CLASS_NO_COPY(AP_AHRS_Backend);

    // structure to retrieve results from backends:
    struct Estimates {
        float roll_rad;
        float pitch_rad;
        float yaw_rad;
        Matrix3f dcm_matrix;
        Vector3f gyro_estimate;
        Vector3f gyro_drift;
        Vector3f accel_ef;
        Vector3f accel_bias;

        Location location;
        bool location_valid;

        bool get_location(Location &loc) const {
            loc = location;
            return location_valid;
        };
    };

    // init sets up INS board orientation
    virtual void init();

    // get the index of the current primary gyro sensor
    virtual uint8_t get_primary_gyro_index(void) const {
#if AP_INERTIALSENSOR_ENABLED
        return AP::ins().get_first_usable_gyro();
#else
        return 0;
#endif
    }

    // Methods
    virtual void update() = 0;

    virtual void get_results(Estimates &results) = 0;

    // returns false if we fail arming checks, in which case the buffer will be populated with a failure message
    // requires_position should be true if horizontal position configuration should be checked
    virtual bool pre_arm_check(bool requires_position, char *failure_msg, uint8_t failure_msg_len) const = 0;

    // check all cores providing consistent attitudes for prearm checks
    virtual bool attitudes_consistent(char *failure_msg, const uint8_t failure_msg_len) const { return true; }

    // see if EKF lane switching is possible to avoid EKF failsafe
    virtual void check_lane_switch(void) {}

    // check if non-compass sensor is providing yaw.  Allows compass pre-arm checks to be bypassed
    virtual bool using_noncompass_for_yaw(void) const { return false; }

    // check if external nav is providing yaw
    virtual bool using_extnav_for_yaw(void) const { return false; }

    // request EKF yaw reset to try and avoid the need for an EKF lane switch or failsafe
    virtual void request_yaw_reset(void) {}

    // set position, velocity and yaw sources to either 0=primary, 1=secondary, 2=tertiary
    virtual void set_posvelyaw_source_set(AP_NavEKF_Source::SourceSetSelection source_set_idx) {}

    // reset the current gyro drift estimate
    //  should be called if gyro offsets are recalculated
    virtual void reset_gyro_drift(void) = 0;

    // reset the current attitude, used on new IMU calibration
    virtual void reset() = 0;

    // get latest altitude estimate above ground level in meters and validity flag
    virtual bool get_hagl(float &height) const WARN_IF_UNUSED { return false; }

    // return a wind estimation vector, in m/s
    virtual bool wind_estimate(Vector3f &wind) const = 0;

    // return an airspeed estimate if available. return true
    // if we have an estimate
    virtual bool airspeed_EAS(float &airspeed_ret) const WARN_IF_UNUSED { return false; }
    virtual bool airspeed_EAS(uint8_t airspeed_index, float &airspeed_ret) const { return false; }

    // return a true airspeed estimate (navigation airspeed) if
    // available. return true if we have an estimate
    bool airspeed_TAS(float &airspeed_ret) const WARN_IF_UNUSED {
        if (!airspeed_EAS(airspeed_ret)) {
            return false;
        }
        airspeed_ret *= get_EAS2TAS();
        return true;
    }

    // get apparent to true airspeed ratio
    static float get_EAS2TAS(void);
    static float get_TAS2EAS(void) { return 1.0/get_EAS2TAS(); }

    // return true if airspeed comes from an airspeed sensor, as
    // opposed to an IMU estimate
    static bool airspeed_sensor_enabled(void) {
    #if AP_AIRSPEED_ENABLED
        const AP_Airspeed *_airspeed = AP::airspeed();
        return _airspeed != nullptr && _airspeed->use() && _airspeed->healthy();
    #else
        return false;
    #endif
    }

    // return true if airspeed comes from a specific airspeed sensor, as
    // opposed to an IMU estimate
    static bool airspeed_sensor_enabled(uint8_t airspeed_index) {
    #if AP_AIRSPEED_ENABLED
        const AP_Airspeed *_airspeed = AP::airspeed();
        return _airspeed != nullptr && _airspeed->use(airspeed_index) && _airspeed->healthy(airspeed_index);
    #else
        return false;
    #endif
    }

    // return a ground vector estimate in meters/second, in North/East order
    virtual Vector2f groundspeed_vector(void) = 0;

    // return a ground velocity in meters/second, North/East/Down
    // order. This will only be accurate if have_inertial_nav() is
    // true
    virtual bool get_velocity_NED(Vector3f &vec) const WARN_IF_UNUSED {
        return false;
    }

    // Get a derivative of the vertical position in m/s which is kinematically consistent with the vertical position is required by some control loops.
    // This is different to the vertical velocity from the EKF which is not always consistent with the vertical position due to the various errors that are being corrected for.
    virtual bool get_vert_pos_rate_D(float &velocity) const = 0;

    //
    virtual bool set_origin(const Location &loc) {
        return false;
    }
    virtual bool get_origin(Location &ret) const = 0;

    // return a position relative to origin in meters, North/East/Down
    // order. This will only be accurate if have_inertial_nav() is
    // true
    virtual bool get_relative_position_NED_origin(Vector3f &vec) const WARN_IF_UNUSED {
        return false;
    }

    // return a position relative to origin in meters, North/East
    // order. Return true if estimate is valid
    virtual bool get_relative_position_NE_origin(Vector2f &vecNE) const WARN_IF_UNUSED {
        return false;
    }

    // return a Down position relative to origin in meters
    // Return true if estimate is valid
    virtual bool get_relative_position_D_origin(float &posD) const WARN_IF_UNUSED {
        return false;
    }

    // return ground speed estimate in meters/second. Used by ground vehicles.
    float groundspeed(void) {
        return groundspeed_vector().length();
    }

    // return true if we will use compass for yaw
    virtual bool use_compass(void) = 0;

    // return the quaternion defining the rotation from NED to XYZ (body) axes
    virtual bool get_quaternion(Quaternion &quat) const WARN_IF_UNUSED = 0;

    // is the AHRS subsystem healthy?
    virtual bool healthy(void) const = 0;

    // true if the AHRS has completed initialisation
    virtual bool initialised(void) const {
        return true;
    };
    virtual bool started(void) const {
        return initialised();
    };

    // return the amount of yaw angle change due to the last yaw angle reset in radians
    // returns the time of the last yaw angle reset or 0 if no reset has ever occurred
    virtual uint32_t getLastYawResetAngle(float &yawAng) {
        return 0;
    };

    // return the amount of NE position change in metres due to the last reset
    // returns the time of the last reset or 0 if no reset has ever occurred
    virtual uint32_t getLastPosNorthEastReset(Vector2f &pos) WARN_IF_UNUSED {
        return 0;
    };

    // return the amount of NE velocity change in metres/sec due to the last reset
    // returns the time of the last reset or 0 if no reset has ever occurred
    virtual uint32_t getLastVelNorthEastReset(Vector2f &vel) const WARN_IF_UNUSED {
        return 0;
    };

    // return the amount of vertical position change due to the last reset in meters
    // returns the time of the last reset or 0 if no reset has ever occurred
    virtual uint32_t getLastPosDownReset(float &posDelta) WARN_IF_UNUSED {
        return 0;
    };

    // Resets the baro so that it reads zero at the current height
    // Resets the EKF height to zero
    // Adjusts the EKf origin height so that the EKF height + origin height is the same as before
    // Returns true if the height datum reset has been performed
    // If using a range finder for height no reset is performed and it returns false
    virtual bool resetHeightDatum(void) WARN_IF_UNUSED {
        return false;
    }

    // return the innovations for the specified instance
    // An out of range instance (eg -1) returns data for the primary instance
    virtual bool get_innovations(Vector3f &velInnov, Vector3f &posInnov, Vector3f &magInnov, float &tasInnov, float &yawInnov) const {
        return false;
    }

    virtual bool get_filter_status(union nav_filter_status &status) const {
        return false;
    }

    // get_variances - provides the innovations normalised using the innovation variance where a value of 0
    // indicates perfect consistency between the measurement and the EKF solution and a value of 1 is the maximum
    // inconsistency that will be accepted by the filter
    // boolean false is returned if variances are not available
    virtual bool get_variances(float &velVar, float &posVar, float &hgtVar, Vector3f &magVar, float &tasVar) const {
        return false;
    }

    // get a source's velocity innovations.  source should be from 0 to 7 (see AP_NavEKF_Source::SourceXY)
    // returns true on success and results are placed in innovations and variances arguments
    virtual bool get_vel_innovations_and_variances_for_source(uint8_t source, Vector3f &innovations, Vector3f &variances) const WARN_IF_UNUSED {
        return false;
    }

    virtual void send_ekf_status_report(class GCS_MAVLINK &link) const = 0;

    // get_hgt_ctrl_limit - get maximum height to be observed by the
    // control loops in meters and a validity flag.  It will return
    // false when no limiting is required
    virtual bool get_hgt_ctrl_limit(float &limit) const WARN_IF_UNUSED { return false; };

    // Set to true if the terrain underneath is stable enough to be used as a height reference
    // this is not related to terrain following
    virtual void set_terrain_hgt_stable(bool stable) {}

    virtual void get_control_limits(float &ekfGndSpdLimit, float &controlScaleXY) const = 0;
};