ardupilot/ArduCopter/AP_Arming.cpp

#include "Copter.h"

// performs pre-arm checks. expects to be called at 1hz.
void AP_Arming_Copter::update(void)
{
    // perform pre-arm checks & display failures every 30 seconds
    static uint8_t pre_arm_display_counter = PREARM_DISPLAY_PERIOD/2;
    pre_arm_display_counter++;
    bool display_fail = false;
    if (pre_arm_display_counter >= PREARM_DISPLAY_PERIOD) {
        display_fail = true;
        pre_arm_display_counter = 0;
    }

    pre_arm_checks(display_fail);
}

bool AP_Arming_Copter::pre_arm_checks(bool display_failure)
{
    const bool passed = run_pre_arm_checks(display_failure);
    set_pre_arm_check(passed);
    return passed;
}

// perform pre-arm checks
//  return true if the checks pass successfully
bool AP_Arming_Copter::run_pre_arm_checks(bool display_failure)
{
    // exit immediately if already armed
    if (copter.motors->armed()) {
        return true;
    }

    // check if motor interlock and Emergency Stop aux switches are used
    // at the same time.  This cannot be allowed.
    if (rc().find_channel_for_option(RC_Channel::AUX_FUNC::MOTOR_INTERLOCK) &&
        rc().find_channel_for_option(RC_Channel::AUX_FUNC::MOTOR_ESTOP)){
        check_failed(display_failure, "Interlock/E-Stop Conflict");
        return false;
    }

    // check if motor interlock aux switch is in use
    // if it is, switch needs to be in disabled position to arm
    // otherwise exit immediately.  This check to be repeated,
    // as state can change at any time.
    if (copter.ap.using_interlock && copter.ap.motor_interlock_switch) {
        check_failed(display_failure, "Motor Interlock Enabled");
    }

    // if pre arm checks are disabled run only the mandatory checks
    if (checks_to_perform == 0) {
        return mandatory_checks(display_failure);
    }

    return fence_checks(display_failure)
        & parameter_checks(display_failure)
        & motor_checks(display_failure)
        & pilot_throttle_checks(display_failure)
        & oa_checks(display_failure) &
        AP_Arming::pre_arm_checks(display_failure);
}

bool AP_Arming_Copter::barometer_checks(bool display_failure)
{
    if (!AP_Arming::barometer_checks(display_failure)) {
        return false;
    }

    bool ret = true;
    // check Baro
    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_BARO)) {
        // Check baro & inav alt are within 1m if EKF is operating in an absolute position mode.
        // Do not check if intending to operate in a ground relative height mode as EKF will output a ground relative height
        // that may differ from the baro height due to baro drift.
        nav_filter_status filt_status = copter.inertial_nav.get_filter_status();
        bool using_baro_ref = (!filt_status.flags.pred_horiz_pos_rel && filt_status.flags.pred_horiz_pos_abs);
        if (using_baro_ref) {
            if (fabsf(copter.inertial_nav.get_altitude() - copter.baro_alt) > PREARM_MAX_ALT_DISPARITY_CM) {
                check_failed(ARMING_CHECK_BARO, display_failure, "Altitude disparity");
                ret = false;
            }
        }
    }
    return ret;
}

bool AP_Arming_Copter::compass_checks(bool display_failure)
{
    bool ret = AP_Arming::compass_checks(display_failure);

    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_COMPASS)) {
        // check compass offsets have been set.  AP_Arming only checks
        // this if learning is off; Copter *always* checks.
        if (!AP::compass().configured()) {
            check_failed(ARMING_CHECK_COMPASS, display_failure, "Compass not calibrated");
            ret = false;
        }
    }

    return ret;
}

bool AP_Arming_Copter::ins_checks(bool display_failure)
{
    bool ret = AP_Arming::ins_checks(display_failure);

    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_INS)) {

        // get ekf attitude (if bad, it's usually the gyro biases)
        if (!pre_arm_ekf_attitude_check()) {
            check_failed(ARMING_CHECK_INS, display_failure, "EKF attitude is bad");
            ret = false;
        }
    }

    return ret;
}

bool AP_Arming_Copter::board_voltage_checks(bool display_failure)
{
    if (!AP_Arming::board_voltage_checks(display_failure)) {
        return false;
    }

    // check battery voltage
    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_VOLTAGE)) {
        if (copter.battery.has_failsafed()) {
            check_failed(ARMING_CHECK_VOLTAGE, display_failure, "Battery failsafe");
            return false;
        }

        // call parent battery checks
        if (!AP_Arming::battery_checks(display_failure)) {
            return false;
        }
    }

    return true;
}

bool AP_Arming_Copter::parameter_checks(bool display_failure)
{
    // check various parameter values
    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_PARAMETERS)) {

        // ensure all rc channels have different functions
        if (rc().duplicate_options_exist()) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Duplicate Aux Switch Options");
            return false;
        }

        // failsafe parameter checks
        if (copter.g.failsafe_throttle) {
            // check throttle min is above throttle failsafe trigger and that the trigger is above ppm encoder's loss-of-signal value of 900
            if (copter.channel_throttle->get_radio_min() <= copter.g.failsafe_throttle_value+10 || copter.g.failsafe_throttle_value < 910) {
                check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Check FS_THR_VALUE");
                return false;
            }
        }

        // lean angle parameter check
        if (copter.aparm.angle_max < 1000 || copter.aparm.angle_max > 8000) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Check ANGLE_MAX");
            return false;
        }

        // acro balance parameter check
#if MODE_ACRO_ENABLED == ENABLED || MODE_SPORT_ENABLED == ENABLED
        if ((copter.g.acro_balance_roll > copter.attitude_control->get_angle_roll_p().kP()) || (copter.g.acro_balance_pitch > copter.attitude_control->get_angle_pitch_p().kP())) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "ACRO_BAL_ROLL/PITCH");
            return false;
        }
#endif

        // pilot-speed-up parameter check
        if (copter.g.pilot_speed_up <= 0) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Check PILOT_SPEED_UP");
            return false;
        }

        #if FRAME_CONFIG == HELI_FRAME
        if (copter.g2.frame_class.get() != AP_Motors::MOTOR_FRAME_HELI_QUAD &&
            copter.g2.frame_class.get() != AP_Motors::MOTOR_FRAME_HELI_DUAL &&
            copter.g2.frame_class.get() != AP_Motors::MOTOR_FRAME_HELI) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Invalid Heli FRAME_CLASS");
            return false;
        }

        // check helicopter parameters
        if (!copter.motors->parameter_check(display_failure)) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Heli motors checks failed");
            return false;
        }
        // Inverted flight feature disabled for Heli Single and Dual frames
        if (copter.g2.frame_class.get() != AP_Motors::MOTOR_FRAME_HELI_QUAD &&
            rc().find_channel_for_option(RC_Channel::aux_func_t::INVERTED) != nullptr) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Inverted flight option not supported");
            return false;
        }
        // Ensure an Aux Channel is configured for motor interlock
        if (rc().find_channel_for_option(RC_Channel::aux_func_t::MOTOR_INTERLOCK) == nullptr) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Motor Interlock not configured");
            return false;
        }

        #else
        if (copter.g2.frame_class.get() == AP_Motors::MOTOR_FRAME_HELI_QUAD ||
            copter.g2.frame_class.get() == AP_Motors::MOTOR_FRAME_HELI_DUAL ||
            copter.g2.frame_class.get() == AP_Motors::MOTOR_FRAME_HELI) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Invalid MultiCopter FRAME_CLASS");
            return false;
        }
        #endif // HELI_FRAME

        // check for missing terrain data
        if (!pre_arm_terrain_check(display_failure)) {
            return false;
        }

        // check adsb avoidance failsafe
#if ADSB_ENABLED == ENABLE
        if (copter.failsafe.adsb) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "ADSB threat detected");
            return false;
        }
#endif

        // ensure controllers are OK with us arming:
        char failure_msg[50];
        if (!copter.pos_control->pre_arm_checks("PSC", failure_msg, ARRAY_SIZE(failure_msg))) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Bad parameter: %s", failure_msg);
            return false;
        }
        if (!copter.attitude_control->pre_arm_checks("ATC", failure_msg, ARRAY_SIZE(failure_msg))) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Bad parameter: %s", failure_msg);
            return false;
        }
    }

    return true;
}

// check motor setup was successful
bool AP_Arming_Copter::motor_checks(bool display_failure)
{
    // check motors initialised  correctly
    if (!copter.motors->initialised_ok()) {
        check_failed(display_failure, "check firmware or FRAME_CLASS");
        return false;
    }

    // if this is a multicopter using ToshibaCAN ESCs ensure MOT_PMW_MIN = 1000, MOT_PWM_MAX = 2000
#if HAL_WITH_UAVCAN && (FRAME_CONFIG != HELI_FRAME)
    bool tcan_active = false;
    const uint8_t num_drivers = AP::can().get_num_drivers();
    for (uint8_t i = 0; i < num_drivers; i++) {
        if (AP::can().get_protocol_type(i) == AP_BoardConfig_CAN::Protocol_Type_ToshibaCAN) {
            tcan_active = true;
        }
    }
    if (tcan_active) {
        if (copter.motors->get_pwm_output_min() != 1000) {
            check_failed(display_failure, "TCAN ESCs require MOT_PWM_MIN=1000");
            return false;
        }
        if (copter.motors->get_pwm_output_max() != 2000) {
            check_failed(display_failure, "TCAN ESCs require MOT_PWM_MAX=2000");
            return false;
        }
    }
#endif

    return true;
}

bool AP_Arming_Copter::pilot_throttle_checks(bool display_failure)
{
    // check throttle is above failsafe throttle
    // this is near the bottom to allow other failures to be displayed before checking pilot throttle
    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_RC)) {
        if (copter.g.failsafe_throttle != FS_THR_DISABLED && copter.channel_throttle->get_radio_in() < copter.g.failsafe_throttle_value) {
            #if FRAME_CONFIG == HELI_FRAME
            const char *failmsg = "Collective below Failsafe";
            #else
            const char *failmsg = "Throttle below Failsafe";
            #endif
            check_failed(ARMING_CHECK_RC, display_failure, "%s", failmsg);
            return false;
        }
    }

    return true;
}

bool AP_Arming_Copter::oa_checks(bool display_failure)
{
#if AC_OAPATHPLANNER_ENABLED == ENABLED
    char failure_msg[50];
    if (copter.g2.oa.pre_arm_check(failure_msg, ARRAY_SIZE(failure_msg))) {
        return true;
    }
    // display failure
    if (strlen(failure_msg) == 0) {
        check_failed(display_failure, "%s", "Check Object Avoidance");
    } else {
        check_failed(display_failure, "%s", failure_msg);
    }
    return false;
#else
    return true;
#endif
}

bool AP_Arming_Copter::rc_calibration_checks(bool display_failure)
{
    const RC_Channel *channels[] = {
        copter.channel_roll,
        copter.channel_pitch,
        copter.channel_throttle,
        copter.channel_yaw
    };

    copter.ap.pre_arm_rc_check = rc_checks_copter_sub(display_failure, channels)
        & AP_Arming::rc_calibration_checks(display_failure);

    return copter.ap.pre_arm_rc_check;
}

// performs pre_arm gps related checks and returns true if passed
bool AP_Arming_Copter::gps_checks(bool display_failure)
{
    // run mandatory gps checks first
    if (!mandatory_gps_checks(display_failure)) {
        AP_Notify::flags.pre_arm_gps_check = false;
        return false;
    }

    // check if flight mode requires GPS
    bool mode_requires_gps = copter.flightmode->requires_GPS();

    // check if fence requires GPS
    bool fence_requires_gps = false;
    #if AC_FENCE == ENABLED
    // if circular or polygon fence is enabled we need GPS
    fence_requires_gps = (copter.fence.get_enabled_fences() & (AC_FENCE_TYPE_CIRCLE | AC_FENCE_TYPE_POLYGON)) > 0;
    #endif

    // return true if GPS is not required
    if (!mode_requires_gps && !fence_requires_gps) {
        AP_Notify::flags.pre_arm_gps_check = true;
        return true;
    }

    // return true immediately if gps check is disabled
    if (!(checks_to_perform == ARMING_CHECK_ALL || checks_to_perform & ARMING_CHECK_GPS)) {
        AP_Notify::flags.pre_arm_gps_check = true;
        return true;
    }

    // warn about hdop separately - to prevent user confusion with no gps lock
    if (copter.gps.get_hdop() > copter.g.gps_hdop_good) {
        check_failed(ARMING_CHECK_GPS, display_failure, "High GPS HDOP");
        AP_Notify::flags.pre_arm_gps_check = false;
        return false;
    }

    // call parent gps checks
    if (!AP_Arming::gps_checks(display_failure)) {
        AP_Notify::flags.pre_arm_gps_check = false;
        return false;
    }

    // if we got here all must be ok
    AP_Notify::flags.pre_arm_gps_check = true;
    return true;
}

// check ekf attitude is acceptable
bool AP_Arming_Copter::pre_arm_ekf_attitude_check()
{
    // get ekf filter status
    nav_filter_status filt_status = copter.inertial_nav.get_filter_status();

    return filt_status.flags.attitude;
}

// check we have required terrain data
bool AP_Arming_Copter::pre_arm_terrain_check(bool display_failure)
{
#if AP_TERRAIN_AVAILABLE && AC_TERRAIN
    // succeed if not using terrain data
    if (!copter.terrain_use()) {
        return true;
    }

    // check if terrain following is enabled, using a range finder but RTL_ALT is higher than rangefinder's max range
    // To-Do: modify RTL return path to fly at or above the RTL_ALT and remove this check

    if (copter.rangefinder_state.enabled && (copter.g.rtl_altitude > copter.rangefinder.max_distance_cm_orient(ROTATION_PITCH_270))) {
        check_failed(ARMING_CHECK_PARAMETERS, display_failure, "RTL_ALT above rangefinder max range");
        return false;
    }

    // show terrain statistics
    uint16_t terr_pending, terr_loaded;
    copter.terrain.get_statistics(terr_pending, terr_loaded);
    bool have_all_data = (terr_pending <= 0);
    if (!have_all_data) {
        check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Waiting for Terrain data");
    }
    return have_all_data;
#else
    return true;
#endif
}

// check nothing is too close to vehicle
bool AP_Arming_Copter::proximity_checks(bool display_failure) const
{
#if PROXIMITY_ENABLED == ENABLED

    if (!AP_Arming::proximity_checks(display_failure)) {
        return false;
    }

    if (!((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_PARAMETERS))) {
        // check is disabled
        return true;
    }

    // get closest object if we might use it for avoidance
#if AC_AVOID_ENABLED == ENABLED
    float angle_deg, distance;
    if (copter.avoid.proximity_avoidance_enabled() && copter.g2.proximity.get_closest_object(angle_deg, distance)) {
        // display error if something is within 60cm
        if (distance <= 0.6f) {
            check_failed(ARMING_CHECK_PARAMETERS, display_failure, "Proximity %d deg, %4.2fm", (int)angle_deg, (double)distance);
            return false;
        }
    }
#endif

#endif
    return true;
}

// performs mandatory gps checks.  returns true if passed
bool AP_Arming_Copter::mandatory_gps_checks(bool display_failure)
{
    // always check if inertial nav has started and is ready
    const AP_AHRS_NavEKF &ahrs = AP::ahrs_navekf();
    if (!ahrs.prearm_healthy()) {
        const char *reason = ahrs.prearm_failure_reason();
        if (reason == nullptr) {
            reason = "AHRS not healthy";
        }
        check_failed(display_failure, "%s", reason);
        return false;
    }

    // check if flight mode requires GPS
    bool mode_requires_gps = copter.flightmode->requires_GPS();

    // check if fence requires GPS
    bool fence_requires_gps = false;
    #if AC_FENCE == ENABLED
    // if circular or polygon fence is enabled we need GPS
    fence_requires_gps = (copter.fence.get_enabled_fences() & (AC_FENCE_TYPE_CIRCLE | AC_FENCE_TYPE_POLYGON)) > 0;
    #endif

    // return true if GPS is not required
    if (!mode_requires_gps && !fence_requires_gps) {
        return true;
    }

    // ensure GPS is ok
    if (!copter.position_ok()) {
        const char *reason = ahrs.prearm_failure_reason();
        if (reason == nullptr) {
            if (!mode_requires_gps && fence_requires_gps) {
                // clarify to user why they need GPS in non-GPS flight mode
                reason = "Fence enabled, need 3D Fix";
            } else {
                reason = "Need 3D Fix";
            }
        }
        check_failed(display_failure, "%s", reason);
        return false;
    }

    // check for GPS glitch (as reported by EKF)
    nav_filter_status filt_status;
    if (ahrs.get_filter_status(filt_status)) {
        if (filt_status.flags.gps_glitching) {
            check_failed(display_failure, "GPS glitching");
            return false;
        }
    }

    // check EKF compass variance is below failsafe threshold
    float vel_variance, pos_variance, hgt_variance, tas_variance;
    Vector3f mag_variance;
    Vector2f offset;
    ahrs.get_variances(vel_variance, pos_variance, hgt_variance, mag_variance, tas_variance, offset);
    if (copter.g.fs_ekf_thresh > 0 && mag_variance.length() >= copter.g.fs_ekf_thresh) {
        check_failed(display_failure, "EKF compass variance");
        return false;
    }

    // check home and EKF origin are not too far
    if (copter.far_from_EKF_origin(ahrs.get_home())) {
        check_failed(display_failure, "EKF-home variance");
        return false;
    }

    // if we got here all must be ok
    return true;
}


// arm_checks - perform final checks before arming
//  always called just before arming.  Return true if ok to arm
//  has side-effect that logging is started
bool AP_Arming_Copter::arm_checks(AP_Arming::Method method)
{
    const AP_AHRS_NavEKF &ahrs = AP::ahrs_navekf();

    // always check if inertial nav has started and is ready
    if (!ahrs.healthy()) {
        check_failed(true, "AHRS not healthy");
        return false;
    }

#ifndef ALLOW_ARM_NO_COMPASS
    // if external source of heading is available, we can skip compass health check
    if (!ahrs.is_ext_nav_used_for_yaw()) {
        const Compass &_compass = AP::compass();
        // check compass health
        if (!_compass.healthy()) {
            check_failed(true, "Compass not healthy");
            return false;
        }
    }
#endif

    Mode::Number control_mode = copter.control_mode;

    // always check if the current mode allows arming
    if (!copter.flightmode->allows_arming(method == AP_Arming::Method::MAVLINK)) {
        check_failed(true, "Mode not armable");
        return false;
    }

    // always check motors
    if (!motor_checks(true)) {
        return false;
    }

    // if we are using motor interlock switch and it's enabled, fail to arm
    // skip check in Throw mode which takes control of the motor interlock
    if (copter.ap.using_interlock && copter.ap.motor_interlock_switch) {
        check_failed(true, "Motor Interlock Enabled");
        return false;
    }

    // if we are not using Emergency Stop switch option, force Estop false to ensure motors
    // can run normally
    if (!rc().find_channel_for_option(RC_Channel::AUX_FUNC::MOTOR_ESTOP)){
        SRV_Channels::set_emergency_stop(false);
        // if we are using motor Estop switch, it must not be in Estop position
    } else if (rc().find_channel_for_option(RC_Channel::AUX_FUNC::MOTOR_ESTOP) && SRV_Channels::get_emergency_stop()){
        gcs().send_text(MAV_SEVERITY_CRITICAL,"Arm: Motor Emergency Stopped");
        return false;
    }

    // succeed if arming checks are disabled
    if (checks_to_perform == 0) {
        return true;
    }

    // check lean angle
    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_INS)) {
        if (degrees(acosf(ahrs.cos_roll()*ahrs.cos_pitch()))*100.0f > copter.aparm.angle_max) {
            check_failed(ARMING_CHECK_INS, true, "Leaning");
            return false;
        }
    }

    // check adsb
#if ADSB_ENABLED == ENABLE
    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_PARAMETERS)) {
        if (copter.failsafe.adsb) {
            check_failed(ARMING_CHECK_PARAMETERS, true, "ADSB threat detected");
            return false;
        }
    }
#endif

    // check throttle
    if ((checks_to_perform == ARMING_CHECK_ALL) || (checks_to_perform & ARMING_CHECK_RC)) {
         #if FRAME_CONFIG == HELI_FRAME
        const char *rc_item = "Collective";
        #else
        const char *rc_item = "Throttle";
        #endif
        // check throttle is not too low - must be above failsafe throttle
        if (copter.g.failsafe_throttle != FS_THR_DISABLED && copter.channel_throttle->get_radio_in() < copter.g.failsafe_throttle_value) {
            check_failed(ARMING_CHECK_RC, true, "%s below failsafe", rc_item);
            return false;
        }

        // check throttle is not too high - skips checks if arming from GCS in Guided
        if (!(method == AP_Arming::Method::MAVLINK && (control_mode == Mode::Number::GUIDED || control_mode == Mode::Number::GUIDED_NOGPS))) {
            // above top of deadband is too always high
            if (copter.get_pilot_desired_climb_rate(copter.channel_throttle->get_control_in()) > 0.0f) {
                check_failed(ARMING_CHECK_RC, true, "%s too high", rc_item);
                return false;
            }
            // in manual modes throttle must be at zero
            #if FRAME_CONFIG != HELI_FRAME
            if ((copter.flightmode->has_manual_throttle() || control_mode == Mode::Number::DRIFT) && copter.channel_throttle->get_control_in() > 0) {
                check_failed(ARMING_CHECK_RC, true, "%s too high", rc_item);
                return false;
            }
            #endif
        }
    }

    // check if safety switch has been pushed
    if (hal.util->safety_switch_state() == AP_HAL::Util::SAFETY_DISARMED) {
        check_failed(true, "Safety Switch");
        return false;
    }

    // superclass method should always be the last thing called; it
    // has side-effects which would need to be cleaned up if one of
    // our arm checks failed
    return AP_Arming::arm_checks(method);
}

// mandatory checks that will be run if ARMING_CHECK is zero or arming forced
bool AP_Arming_Copter::mandatory_checks(bool display_failure)
{
    // call mandatory gps checks and update notify status because regular gps checks will not run
    const bool result = mandatory_gps_checks(display_failure);
    AP_Notify::flags.pre_arm_gps_check = result;
    return result;
}

void AP_Arming_Copter::set_pre_arm_check(bool b)
{
    copter.ap.pre_arm_check = b;
    AP_Notify::flags.pre_arm_check = b;
}

bool AP_Arming_Copter::arm(const AP_Arming::Method method, const bool do_arming_checks)
{
    static bool in_arm_motors = false;

    // exit immediately if already in this function
    if (in_arm_motors) {
        return false;
    }
    in_arm_motors = true;

    // return true if already armed
    if (copter.motors->armed()) {
        in_arm_motors = false;
        return true;
    }

    if (!AP_Arming::arm(method, do_arming_checks)) {
        AP_Notify::events.arming_failed = true;
        in_arm_motors = false;
        return false;
    }

    // let logger know that we're armed (it may open logs e.g.)
    AP::logger().set_vehicle_armed(true);

    // disable cpu failsafe because initialising everything takes a while
    copter.failsafe_disable();

    // notify that arming will occur (we do this early to give plenty of warning)
    AP_Notify::flags.armed = true;
    // call notify update a few times to ensure the message gets out
    for (uint8_t i=0; i<=10; i++) {
        AP::notify().update();
    }

#if HIL_MODE != HIL_MODE_DISABLED || CONFIG_HAL_BOARD == HAL_BOARD_SITL
    gcs().send_text(MAV_SEVERITY_INFO, "Arming motors");
#endif

    // Remember Orientation
    // --------------------
    copter.init_simple_bearing();

    AP_AHRS_NavEKF &ahrs = AP::ahrs_navekf();

    copter.initial_armed_bearing = ahrs.yaw_sensor;

    if (!ahrs.home_is_set()) {
        // Reset EKF altitude if home hasn't been set yet (we use EKF altitude as substitute for alt above home)
        ahrs.resetHeightDatum();
        AP::logger().Write_Event(DATA_EKF_ALT_RESET);

        // we have reset height, so arming height is zero
        copter.arming_altitude_m = 0;
    } else if (!ahrs.home_is_locked()) {
        // Reset home position if it has already been set before (but not locked)
        if (!copter.set_home_to_current_location(false)) {
            // ignore failure
        }

        // remember the height when we armed
        copter.arming_altitude_m = copter.inertial_nav.get_altitude() * 0.01;
    }
    copter.update_super_simple_bearing(false);

    // Reset SmartRTL return location. If activated, SmartRTL will ultimately try to land at this point
#if MODE_SMARTRTL_ENABLED == ENABLED
    copter.g2.smart_rtl.set_home(copter.position_ok());
#endif

    // enable gps velocity based centrefugal force compensation
    ahrs.set_correct_centrifugal(true);
    hal.util->set_soft_armed(true);

#if SPRAYER_ENABLED == ENABLED
    // turn off sprayer's test if on
    copter.sprayer.test_pump(false);
#endif

    // enable output to motors
    copter.enable_motor_output();

    // finally actually arm the motors
    copter.motors->armed(true);

    AP::logger().Write_Event(DATA_ARMED);

    // log flight mode in case it was changed while vehicle was disarmed
    AP::logger().Write_Mode((uint8_t)copter.control_mode, copter.control_mode_reason);

    // re-enable failsafe
    copter.failsafe_enable();

    // perf monitor ignores delay due to arming
    AP::scheduler().perf_info.ignore_this_loop();

    // flag exiting this function
    in_arm_motors = false;

    // Log time stamp of arming event
    copter.arm_time_ms = millis();

    // Start the arming delay
    copter.ap.in_arming_delay = true;

    // assumed armed without a arming, switch. Overridden in switches.cpp
    copter.ap.armed_with_switch = false;

    // return success
    return true;
}

// arming.disarm - disarm motors
bool AP_Arming_Copter::disarm()
{
    // return immediately if we are already disarmed
    if (!copter.motors->armed()) {
        return true;
    }

    if (!AP_Arming::disarm()) {
        return false;
    }

#if HIL_MODE != HIL_MODE_DISABLED || CONFIG_HAL_BOARD == HAL_BOARD_SITL
    gcs().send_text(MAV_SEVERITY_INFO, "Disarming motors");
#endif

    AP_AHRS_NavEKF &ahrs = AP::ahrs_navekf();

    // save compass offsets learned by the EKF if enabled
    Compass &compass = AP::compass();
    if (ahrs.use_compass() && compass.get_learn_type() == Compass::LEARN_EKF) {
        for(uint8_t i=0; i<COMPASS_MAX_INSTANCES; i++) {
            Vector3f magOffsets;
            if (ahrs.getMagOffsets(i, magOffsets)) {
                compass.set_and_save_offsets(i, magOffsets);
            }
        }
    }

#if AUTOTUNE_ENABLED == ENABLED
    // save auto tuned parameters
    if (copter.flightmode == &copter.mode_autotune) {
        copter.mode_autotune.save_tuning_gains();
    } else {
        copter.mode_autotune.reset();
    }
#endif

    // we are not in the air
    copter.set_land_complete(true);
    copter.set_land_complete_maybe(true);

    AP::logger().Write_Event(DATA_DISARMED);

    // send disarm command to motors
    copter.motors->armed(false);

#if MODE_AUTO_ENABLED == ENABLED
    // reset the mission
    copter.mode_auto.mission.reset();
#endif

    AP::logger().set_vehicle_armed(false);

    // disable gps velocity based centrefugal force compensation
    ahrs.set_correct_centrifugal(false);
    hal.util->set_soft_armed(false);

    copter.ap.in_arming_delay = false;

    return true;
}