引言：ArduPilot代码兼容无人机，无人车，UUV，帆船等多种vehicle，本文以Copter为例，说明代码中是如何完成模式切换的。

各个模式的init

首先定位在系统初始化中，即system.cpp中的 rc().init(); 执行跳转查看函数
init_aux_all(); -->reset_mode_switch(); -->c->reset_mode_switch();–>read_mode_switch();

void RC_Channel::read_mode_switch()
{
    // calculate position of flight mode switch
    const uint16_t pulsewidth = get_radio_in();
    if (pulsewidth <= 900 || pulsewidth >= 2200) {
        return;  // This is an error condition
    }

    modeswitch_pos_t position;
    if      (pulsewidth < 1231) position = 0;
    else if (pulsewidth < 1361) position = 1;
    else if (pulsewidth < 1491) position = 2;
    else if (pulsewidth < 1621) position = 3;
    else if (pulsewidth < 1750) position = 4;
    else position = 5;

    if (!debounce_completed(position)) {
        return;
    }

    // set flight mode and simple mode setting
    mode_switch_changed(position);
}

mode_switch_changed为虚函数，在Copter中进行了实例化。

void RC_Channel_Copter::mode_switch_changed(modeswitch_pos_t new_pos)
{
    if (new_pos < 0 || (uint8_t)new_pos > copter.num_flight_modes) {
        // should not have been called
        return;
    }

    if (!copter.set_mode((Mode::Number)copter.flight_modes[new_pos].get(), ModeReason::RC_COMMAND)) {
        // alert user to mode change failure
        if (copter.ap.initialised) {
            AP_Notify::events.user_mode_change_failed = 1;
        }
        return;
    }

    // play a tone
    // alert user to mode change (except if autopilot is just starting up)
    if (copter.ap.initialised) {
        AP_Notify::events.user_mode_change = 1;
    }

    if (!rc().find_channel_for_option(AUX_FUNC::SIMPLE_MODE) &&
        !rc().find_channel_for_option(AUX_FUNC::SUPERSIMPLE_MODE)) {
        // if none of the Aux Switches are set to Simple or Super Simple Mode then
        // set Simple Mode using stored parameters from EEPROM
        if (BIT_IS_SET(copter.g.super_simple, new_pos)) {
            copter.set_simple_mode(2);
        } else {
            copter.set_simple_mode(BIT_IS_SET(copter.g.simple_modes, new_pos));
        }
    }
}

其中下图所示内容为关键点：

Mode::Number为模式的所有类别。

enum class Number : uint8_t {
    STABILIZE =     0,  // manual airframe angle with manual throttle
    ACRO =          1,  // manual body-frame angular rate with manual throttle
    ALT_HOLD =      2,  // manual airframe angle with automatic throttle
    AUTO =          3,  // fully automatic waypoint control using mission commands
    GUIDED =        4,  // fully automatic fly to coordinate or fly at velocity/direction using GCS immediate commands
    LOITER =        5,  // automatic horizontal acceleration with automatic throttle
    RTL =           6,  // automatic return to launching point
    CIRCLE =        7,  // automatic circular flight with automatic throttle
    LAND =          9,  // automatic landing with horizontal position control
    DRIFT =        11,  // semi-automous position, yaw and throttle control
    SPORT =        13,  // manual earth-frame angular rate control with manual throttle
    FLIP =         14,  // automatically flip the vehicle on the roll axis
    AUTOTUNE =     15,  // automatically tune the vehicle's roll and pitch gains
    POSHOLD =      16,  // automatic position hold with manual override, with automatic throttle
    BRAKE =        17,  // full-brake using inertial/GPS system, no pilot input
    THROW =        18,  // throw to launch mode using inertial/GPS system, no pilot input
    AVOID_ADSB =   19,  // automatic avoidance of obstacles in the macro scale - e.g. full-sized aircraft
    GUIDED_NOGPS = 20,  // guided mode but only accepts attitude and altitude
    SMART_RTL =    21,  // SMART_RTL returns to home by retracing its steps
    FLOWHOLD  =    22,  // FLOWHOLD holds position with optical flow without rangefinder
    FOLLOW    =    23,  // follow attempts to follow another vehicle or ground station
    ZIGZAG    =    24,  // ZIGZAG mode is able to fly in a zigzag manner with predefined point A and point B
    SYSTEMID  =    25,  // System ID mode produces automated system identification signals in the controllers
    AUTOROTATE =   26,  // Autonomous autorotation
};

而SetMode函数如下，其中关键语句如下图所示：

// set_mode - change flight mode and perform any necessary initialisation
// optional force parameter used to force the flight mode change (used only first time mode is set)
// returns true if mode was successfully set
// ACRO, STABILIZE, ALTHOLD, LAND, DRIFT and SPORT can always be set successfully but the return state of other flight modes should be checked and the caller should deal with failures appropriately
bool Copter::set_mode(Mode::Number mode, ModeReason reason)
{

    // return immediately if we are already in the desired mode
    if (mode == control_mode) {
        control_mode_reason = reason;
        return true;
    }

    Mode *new_flightmode = mode_from_mode_num((Mode::Number)mode);
    if (new_flightmode == nullptr) {
        gcs().send_text(MAV_SEVERITY_WARNING,"No such mode");
        AP::logger().Write_Error(LogErrorSubsystem::FLIGHT_MODE, LogErrorCode(mode));
        return false;
    }

    bool ignore_checks = !motors->armed();   // allow switching to any mode if disarmed. We rely on the arming check to perform

#if FRAME_CONFIG == HELI_FRAME
    // do not allow helis to enter a non-manual throttle mode if the
    // rotor runup is not complete
    if (!ignore_checks && !new_flightmode->has_manual_throttle() &&
        (motors->get_spool_state() == AP_Motors::SpoolState::SPOOLING_UP || motors->get_spool_state() == AP_Motors::SpoolState::SPOOLING_DOWN)) {
        #if MODE_AUTOROTATE_ENABLED == ENABLED
            //if the mode being exited is the autorotation mode allow mode change despite rotor not being at
            //full speed. This will reduce altitude loss on bail-outs back to non-manual throttle modes
            bool in_autorotation_check = (flightmode != &mode_autorotate || new_flightmode != &mode_autorotate);
        #else
            bool in_autorotation_check = false;
        #endif

        if (!in_autorotation_check) {
            gcs().send_text(MAV_SEVERITY_WARNING,"Flight mode change failed");
            AP::logger().Write_Error(LogErrorSubsystem::FLIGHT_MODE, LogErrorCode(mode));
            return false;
        }
    }
#endif

#if FRAME_CONFIG != HELI_FRAME
    // ensure vehicle doesn't leap off the ground if a user switches
    // into a manual throttle mode from a non-manual-throttle mode
    // (e.g. user arms in guided, raises throttle to 1300 (not enough to
    // trigger auto takeoff), then switches into manual):
    bool user_throttle = new_flightmode->has_manual_throttle();
#if MODE_DRIFT_ENABLED == ENABLED
    if (new_flightmode == &mode_drift) {
        user_throttle = true;
    }
#endif
    if (!ignore_checks &&
        ap.land_complete &&
        user_throttle &&
        !copter.flightmode->has_manual_throttle() &&
        new_flightmode->get_pilot_desired_throttle() > copter.get_non_takeoff_throttle()) {
        gcs().send_text(MAV_SEVERITY_WARNING, "Mode change failed: throttle too high");
        AP::logger().Write_Error(LogErrorSubsystem::FLIGHT_MODE, LogErrorCode(mode));
        return false;
    }
#endif

    if (!ignore_checks &&
        new_flightmode->requires_GPS() &&
        !copter.position_ok()) {
        gcs().send_text(MAV_SEVERITY_WARNING, "Mode change failed: %s requires position", new_flightmode->name());
        AP::logger().Write_Error(LogErrorSubsystem::FLIGHT_MODE, LogErrorCode(mode));
        return false;
    }

    if (!new_flightmode->init(ignore_checks)) {
        gcs().send_text(MAV_SEVERITY_WARNING,"Flight mode change failed");
        AP::logger().Write_Error(LogErrorSubsystem::FLIGHT_MODE, LogErrorCode(mode));
        return false;
    }

    // perform any cleanup required by previous flight mode
    exit_mode(flightmode, new_flightmode);

    // store previous flight mode (only used by tradeheli's autorotation)
    prev_control_mode = control_mode;

    // update flight mode
    flightmode = new_flightmode;
    control_mode = mode;
    control_mode_reason = reason;
    logger.Write_Mode((uint8_t)control_mode, reason);
    gcs().send_message(MSG_HEARTBEAT);

#if ADSB_ENABLED == ENABLED
    adsb.set_is_auto_mode((mode == Mode::Number::AUTO) || (mode == Mode::Number::RTL) || (mode == Mode::Number::GUIDED));
#endif

#if AC_FENCE == ENABLED
    // pilot requested flight mode change during a fence breach indicates pilot is attempting to manually recover
    // this flight mode change could be automatic (i.e. fence, battery, GPS or GCS failsafe)
    // but it should be harmless to disable the fence temporarily in these situations as well
    fence.manual_recovery_start();
#endif

#if CAMERA == ENABLED
    camera.set_is_auto_mode(control_mode == Mode::Number::AUTO);
#endif

    // update notify object
    notify_flight_mode();

    // return success
    return true;
}

即完成了对应模式的初始化工作。

各个模式的Run

首先定位到Copter.cpp中，找到fast_loop中的update_flight_mode(); 可以看到里面即可以定位到模式的Run。

// update_flight_mode - calls the appropriate attitude controllers based on flight mode
// called at 100hz or more
void Copter::update_flight_mode()
{
    surface_tracking.invalidate_for_logging();  // invalidate surface tracking alt, flight mode will set to true if used

    flightmode->run();
}

同时，在rc_loop中实时查看模式的切换

// rc_loops - reads user input from transmitter/receiver
// called at 100hz
void Copter::rc_loop()
{
    // Read radio and 3-position switch on radio
    // -----------------------------------------
    read_radio();
    rc().read_mode_switch();
}

通过rc().read_mode_switch(); --> c->read_mode_switch(); 随后执行就与上文所提到的初始化进入了相同的地方。

注明

下图所示代码位于SetMode函数中，表示判断是否可以进行模式切换功能，具体含义参看if判断。同时如果切换成功，则进入exit_mode函数中，该函数完成模式的过渡过程。

参考：Ardupilot 高度控制代码整理(超长篇)