ardupilot/libraries/AP_Compass/AP_Compass_SITL.cpp

#include "AP_Compass_SITL.h"

#if AP_COMPASS_SITL_ENABLED

#include <AP_HAL/AP_HAL.h>

extern const AP_HAL::HAL& hal;

AP_Compass_SITL::AP_Compass_SITL(uint8_t _sitl_instance) :
    _sitl(AP::sitl()),
    sitl_instance(_sitl_instance)
{
    if (sitl_instance > ARRAY_SIZE(_sitl->mag_devid)) {
        return;
    }

            const uint32_t dev_id = _sitl->mag_devid[sitl_instance];
            if (dev_id == 0) {
                return;
            }
            if (!register_compass(dev_id)) {
                return;
            }
                if (_sitl->mag_save_ids) {
                    // save so the compass always comes up configured in SITL
                    save_dev_id();
                }
                set_rotation(ROTATION_NONE);

        // Scroll through the registered compasses, and set the offsets
            if (_compass.get_offsets(instance).is_zero()) {
                _compass.set_offsets(instance, _sitl->mag_ofs[sitl_instance]);
            }

        // we want to simulate a calibrated compass by default, so set
        // scale to 1
        AP_Param::set_default_by_name("COMPASS_SCALE", 1);
        AP_Param::set_default_by_name("COMPASS_SCALE2", 1);
        AP_Param::set_default_by_name("COMPASS_SCALE3", 1);

        // make first compass external
        if (sitl_instance == 0) {
            set_external(true);
        }

        hal.scheduler->register_timer_process(FUNCTOR_BIND(this, &AP_Compass_SITL::_timer, void));
}


/*
  create correction matrix for diagonals and off-diagonals
*/
void AP_Compass_SITL::_setup_eliptical_correcion()
{
    Vector3f diag = _sitl->mag_diag[sitl_instance].get();
    if (diag.is_zero()) {
        diag = {1,1,1};
    }
    const Vector3f &diagonals = diag;
    const Vector3f &offdiagonals = _sitl->mag_offdiag[sitl_instance];
    
    if (diagonals == _last_dia && offdiagonals == _last_odi) {
        return;
    }
    
    _eliptical_corr = Matrix3f(diagonals.x,    offdiagonals.x, offdiagonals.y,
                               offdiagonals.x, diagonals.y,    offdiagonals.z,
                               offdiagonals.y, offdiagonals.z, diagonals.z);
    if (!_eliptical_corr.invert()) {
        _eliptical_corr.identity();
    }
    _last_dia = diag;
    _last_odi = offdiagonals;
}

void AP_Compass_SITL::_timer()
{
    // TODO: Refactor delay buffer with AP_Baro_SITL.

    // Sampled at 100Hz
    uint32_t now = AP_HAL::millis();
    if ((now - _last_sample_time) < 10) {
        return;
    }
    _last_sample_time = now;

    // calculate sensor noise and add to 'truth' field in body frame
    // units are milli-Gauss
    Vector3f noise = rand_vec3f() * _sitl->mag_noise;
    Vector3f new_mag_data = _sitl->state.bodyMagField + noise;

    // add delay
    uint32_t best_time_delta = 1000; // initialise large time representing buffer entry closest to current time - delay.
    uint8_t best_index = 0; // initialise number representing the index of the entry in buffer closest to delay.

    // storing data from sensor to buffer
    if (now - last_store_time >= 10) { // store data every 10 ms.
        last_store_time = now;
        if (store_index > buffer_length-1) { // reset buffer index if index greater than size of buffer
            store_index = 0;
        }
        buffer[store_index].data = new_mag_data; // add data to current index
        buffer[store_index].time = last_store_time; // add time to current index
        store_index = store_index + 1; // increment index
    }

    // return delayed measurement
    uint32_t delayed_time = now - _sitl->mag_delay; // get time corresponding to delay
    // find data corresponding to delayed time in buffer
    for (uint8_t i=0; i<=buffer_length-1; i++) {
        // find difference between delayed time and time stamp in buffer
        uint32_t time_delta = abs((int32_t)(delayed_time - buffer[i].time));
        // if this difference is smaller than last delta, store this time
        if (time_delta < best_time_delta) {
            best_index= i;
            best_time_delta = time_delta;
        }
    }
    if (best_time_delta < 1000) { // only output stored state if < 1 sec retrieval error
        new_mag_data = buffer[best_index].data;
    }

        _setup_eliptical_correcion();
        Vector3f f = (_eliptical_corr * new_mag_data) - _sitl->mag_ofs[sitl_instance].get();
        // rotate compass
        f.rotate_inverse((enum Rotation)_sitl->mag_orient[sitl_instance].get());
        f.rotate(get_board_orientation());
        // SIM_BRD_TRIM: rigid board mounting offset (same rotation applied to
        // the accels and gyros), keeping the compass consistent with the IMU
        const Vector3f &board_trim = _sitl->board_trim.get();
        if (!board_trim.is_zero()) {
            Matrix3f trim_rotation;
            trim_rotation.from_euler(board_trim.x, board_trim.y, board_trim.z);
            f = trim_rotation.transposed() * f;
        }
        // scale the compass to simulate sensor scale factor errors
        f *= _sitl->mag_scaling[sitl_instance];

        switch (_sitl->mag_fail[sitl_instance]) {
        case 0:
            accumulate_sample(f, 10);
            _last_data = f;
            break;
        case 1:
            // no data
            break;
        case 2:
            // frozen compass
            accumulate_sample(_last_data, 10);
            break;
        }
}

#endif  // AP_COMPASS_SITL_ENABLED