LibrePilot/flight/modules/Stabilization/stabilization.c

/**
 ******************************************************************************
 * @addtogroup OpenPilotModules OpenPilot Modules
 * @{
 * @addtogroup StabilizationModule Stabilization Module
 * @brief Stabilization PID loops in an airframe type independent manner
 * @note This object updates the @ref ActuatorDesired "Actuator Desired" based on the
 * PID loops on the @ref AttitudeDesired "Attitude Desired" and @ref AttitudeState "Attitude State"
 * @{
 *
 * @file       stabilization.c
 * @author     The OpenPilot Team, http://www.openpilot.org Copyright (C) 2010.
 * @brief      Attitude stabilization module.
 *
 * @see        The GNU Public License (GPL) Version 3
 *
 *****************************************************************************/
/*
 * 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, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include <openpilot.h>
#include <pios_struct_helper.h>
#include "stabilization.h"
#include "stabilizationsettings.h"
#include "stabilizationbank.h"
#include "stabilizationsettingsbank1.h"
#include "stabilizationsettingsbank2.h"
#include "stabilizationsettingsbank3.h"
#include "actuatordesired.h"
#include "ratedesired.h"
#include "relaytuning.h"
#include "relaytuningsettings.h"
#include "stabilizationdesired.h"
#include "attitudestate.h"
#include "airspeedstate.h"
#include "gyrostate.h"
#include "flightstatus.h"
#include "manualcontrolsettings.h"
#include "manualcontrol.h" // Just to get a macro
#include "taskinfo.h"

// Math libraries
#include "CoordinateConversions.h"
#include "pid.h"
#include "sin_lookup.h"

// Includes for various stabilization algorithms
#include "relay_tuning.h"
#include "virtualflybar.h"

// Includes for various stabilization algorithms
#include "relay_tuning.h"

// Private constants
#define MAX_QUEUE_SIZE      1

#if defined(PIOS_STABILIZATION_STACK_SIZE)
#define STACK_SIZE_BYTES    PIOS_STABILIZATION_STACK_SIZE
#else
#define STACK_SIZE_BYTES    790
#endif

#define TASK_PRIORITY       (tskIDLE_PRIORITY + 4)
#define FAILSAFE_TIMEOUT_MS 30

// number of flight mode switch positions
#define NUM_FMS_POSITIONS   6

// The PID_RATE_ROLL set is used by Rate mode and the rate portion of Attitude mode
// The PID_RATE set is used by the attitude portion of Attitude mode
// The PID_RATEA_ROLL set is used by Rattitude mode because it needs to maintain
// - two independant rate PIDs because it does rate and attitude simultaneously
enum { PID_RATE_ROLL, PID_RATE_PITCH, PID_RATE_YAW, PID_ROLL, PID_PITCH, PID_YAW, PID_RATEA_ROLL, PID_RATEA_PITCH, PID_RATEA_YAW, PID_MAX };
enum { RATE_P, RATE_I, RATE_D, RATE_LIMIT, RATE_OFFSET };
enum { ATT_P, ATT_I, ATT_LIMIT, ATT_OFFSET };

// Private variables
static xTaskHandle taskHandle;
static StabilizationSettingsData settings;
static xQueueHandle queue;
float gyro_alpha = 0;
float axis_lock_accum[3] = { 0, 0, 0 };
uint8_t max_axis_lock     = 0;
uint8_t max_axislock_rate = 0;
float weak_leveling_kp    = 0;
uint8_t weak_leveling_max = 0;
bool lowThrottleZeroIntegral;
bool lowThrottleZeroAxis[MAX_AXES];
float vbar_decay    = 0.991f;
struct pid pids[PID_MAX];

int cur_flight_mode = -1;

static uint8_t rattitude_anti_windup;
static float cruise_control_min_throttle;
static float cruise_control_max_throttle;
static uint8_t cruise_control_max_angle;
static float cruise_control_max_power_factor;
static float cruise_control_power_trim;
static int8_t cruise_control_inverted_power_switch;
static float cruise_control_neutral_thrust;
static uint8_t cruise_control_flight_mode_switch_pos_enable[NUM_FMS_POSITIONS];

// Private functions
static void stabilizationTask(void *parameters);
static float bound(float val, float range);
static void ZeroPids(void);
static void SettingsUpdatedCb(UAVObjEvent *ev);
static void BankUpdatedCb(UAVObjEvent *ev);
static void SettingsBankUpdatedCb(UAVObjEvent *ev);

static float stab_log2f(float x);
static float stab_powf(float x, uint8_t p);

/**
 * Module initialization
 */
int32_t StabilizationStart()
{
    // Initialize variables
    // Create object queue
    queue = xQueueCreate(MAX_QUEUE_SIZE, sizeof(UAVObjEvent));

    // Listen for updates.
    // AttitudeStateConnectQueue(queue);
    GyroStateConnectQueue(queue);

    StabilizationSettingsConnectCallback(SettingsUpdatedCb);
    SettingsUpdatedCb(StabilizationSettingsHandle());

    StabilizationBankConnectCallback(BankUpdatedCb);

    StabilizationSettingsBank1ConnectCallback(SettingsBankUpdatedCb);
    StabilizationSettingsBank2ConnectCallback(SettingsBankUpdatedCb);
    StabilizationSettingsBank3ConnectCallback(SettingsBankUpdatedCb);


    // Start main task
    xTaskCreate(stabilizationTask, (signed char *)"Stabilization", STACK_SIZE_BYTES / 4, NULL, TASK_PRIORITY, &taskHandle);
    PIOS_TASK_MONITOR_RegisterTask(TASKINFO_RUNNING_STABILIZATION, taskHandle);
#ifdef PIOS_INCLUDE_WDG
    PIOS_WDG_RegisterFlag(PIOS_WDG_STABILIZATION);
#endif
    return 0;
}

/**
 * Module initialization
 */
int32_t StabilizationInitialize()
{
    // stop the compile if the number of switch positions changes, but has not been changed here
    PIOS_STATIC_ASSERT(NUM_FMS_POSITIONS == sizeof(((ManualControlSettingsData *)0)->FlightModePosition) / sizeof((((ManualControlSettingsData *)0)->FlightModePosition)[0]));

    // Initialize variables
    StabilizationSettingsInitialize();
    StabilizationBankInitialize();
    StabilizationSettingsBank1Initialize();
    StabilizationSettingsBank2Initialize();
    StabilizationSettingsBank3Initialize();
    ActuatorDesiredInitialize();
#ifdef DIAG_RATEDESIRED
    RateDesiredInitialize();
#endif
#ifdef REVOLUTION
    AirspeedStateInitialize();
#endif
    // Code required for relay tuning
    sin_lookup_initalize();
    RelayTuningSettingsInitialize();
    RelayTuningInitialize();

    return 0;
}

MODULE_INITCALL(StabilizationInitialize, StabilizationStart);

/**
 * Module task
 */
static void stabilizationTask(__attribute__((unused)) void *parameters)
{
    UAVObjEvent ev;

    uint32_t timeval = PIOS_DELAY_GetRaw();

    ActuatorDesiredData actuatorDesired;
    StabilizationDesiredData stabDesired;
    RateDesiredData rateDesired;
    AttitudeStateData attitudeState;
    GyroStateData gyroStateData;
    FlightStatusData flightStatus;
    StabilizationBankData stabBank;


#ifdef REVOLUTION
    AirspeedStateData airspeedState;
#endif

    SettingsUpdatedCb((UAVObjEvent *)NULL);

    // Main task loop
    ZeroPids();
    while (1) {
        float dT;

#ifdef PIOS_INCLUDE_WDG
        PIOS_WDG_UpdateFlag(PIOS_WDG_STABILIZATION);
#endif

        // Wait until the Gyro object is updated, if a timeout then go to failsafe
        if (xQueueReceive(queue, &ev, FAILSAFE_TIMEOUT_MS / portTICK_RATE_MS) != pdTRUE) {
            AlarmsSet(SYSTEMALARMS_ALARM_STABILIZATION, SYSTEMALARMS_ALARM_WARNING);
            continue;
        }

        dT = PIOS_DELAY_DiffuS(timeval) * 1.0e-6f;
        timeval = PIOS_DELAY_GetRaw();

        FlightStatusGet(&flightStatus);
        StabilizationDesiredGet(&stabDesired);
        AttitudeStateGet(&attitudeState);
        GyroStateGet(&gyroStateData);
        StabilizationBankGet(&stabBank);
#ifdef DIAG_RATEDESIRED
        RateDesiredGet(&rateDesired);
#endif
        uint8_t flight_mode_switch_position;
        ManualControlCommandFlightModeSwitchPositionGet(&flight_mode_switch_position);

        if (cur_flight_mode != flight_mode_switch_position) {
            cur_flight_mode = flight_mode_switch_position;
            SettingsBankUpdatedCb(NULL);
        }

#ifdef REVOLUTION
        float speedScaleFactor;
        // Scale PID coefficients based on current airspeed estimation - needed for fixed wing planes
        AirspeedStateGet(&airspeedState);
        if (settings.ScaleToAirspeed < 0.1f || airspeedState.CalibratedAirspeed < 0.1f) {
            // feature has been turned off
            speedScaleFactor = 1.0f;
        } else {
            // scale the factor to be 1.0 at the specified airspeed (for example 10m/s) but scaled by 1/speed^2
            speedScaleFactor = (settings.ScaleToAirspeed * settings.ScaleToAirspeed) / (airspeedState.CalibratedAirspeed * airspeedState.CalibratedAirspeed);
            if (speedScaleFactor < settings.ScaleToAirspeedLimits.Min) {
                speedScaleFactor = settings.ScaleToAirspeedLimits.Min;
            }
            if (speedScaleFactor > settings.ScaleToAirspeedLimits.Max) {
                speedScaleFactor = settings.ScaleToAirspeedLimits.Max;
            }
        }
#else
        const float speedScaleFactor = 1.0f;
#endif

#if defined(PIOS_QUATERNION_STABILIZATION)
        // Quaternion calculation of error in each axis.  Uses more memory.
        float rpy_desired[3];
        float q_desired[4];
        float q_error[4];
        float local_error[3];

        // Essentially zero errors for anything in rate or none
        if (stabDesired.StabilizationMode.Roll == STABILIZATIONDESIRED_STABILIZATIONMODE_ATTITUDE) {
            rpy_desired[0] = stabDesired.Roll;
        } else {
            rpy_desired[0] = attitudeState.Roll;
        }

        if (stabDesired.StabilizationMode.Pitch == STABILIZATIONDESIRED_STABILIZATIONMODE_ATTITUDE) {
            rpy_desired[1] = stabDesired.Pitch;
        } else {
            rpy_desired[1] = attitudeState.Pitch;
        }

        if (stabDesired.StabilizationMode.Yaw == STABILIZATIONDESIRED_STABILIZATIONMODE_ATTITUDE) {
            rpy_desired[2] = stabDesired.Yaw;
        } else {
            rpy_desired[2] = attitudeState.Yaw;
        }

        RPY2Quaternion(rpy_desired, q_desired);
        quat_inverse(q_desired);
        quat_mult(q_desired, &attitudeState.q1, q_error);
        quat_inverse(q_error);
        Quaternion2RPY(q_error, local_error);

#else /* if defined(PIOS_QUATERNION_STABILIZATION) */
        // Simpler algorithm for CC, less memory
        float local_error[3] = { stabDesired.Roll - attitudeState.Roll,
                                 stabDesired.Pitch - attitudeState.Pitch,
                                 stabDesired.Yaw - attitudeState.Yaw };
        // find shortest way
        float modulo = fmodf(local_error[2] + 180.0f, 360.0f);
        if (modulo < 0) {
            local_error[2] = modulo + 180.0f;
        } else {
            local_error[2] = modulo - 180.0f;
        }
#endif /* if defined(PIOS_QUATERNION_STABILIZATION) */

        float gyro_filtered[3];
        gyro_filtered[0] = gyro_filtered[0] * gyro_alpha + gyroStateData.x * (1 - gyro_alpha);
        gyro_filtered[1] = gyro_filtered[1] * gyro_alpha + gyroStateData.y * (1 - gyro_alpha);
        gyro_filtered[2] = gyro_filtered[2] * gyro_alpha + gyroStateData.z * (1 - gyro_alpha);

        float *stabDesiredAxis     = &stabDesired.Roll;
        float *actuatorDesiredAxis = &actuatorDesired.Roll;
        float *rateDesiredAxis     = &rateDesired.Roll;

        ActuatorDesiredGet(&actuatorDesired);

        // A flag to track which stabilization mode each axis is in
        static uint8_t previous_mode[MAX_AXES] = { 255, 255, 255 };
        bool error = false;

        // Run the selected stabilization algorithm on each axis:
        for (uint8_t i = 0; i < MAX_AXES; i++) {
            // Check whether this axis mode needs to be reinitialized
            bool reinit = (cast_struct_to_array(stabDesired.StabilizationMode, stabDesired.StabilizationMode.Roll)[i] != previous_mode[i]);
            previous_mode[i] = cast_struct_to_array(stabDesired.StabilizationMode, stabDesired.StabilizationMode.Roll)[i];

            // Apply the selected control law
            switch (cast_struct_to_array(stabDesired.StabilizationMode, stabDesired.StabilizationMode.Roll)[i]) {
            case STABILIZATIONDESIRED_STABILIZATIONMODE_RATE:
                if (reinit) {
                    pids[PID_RATE_ROLL + i].iAccumulator = 0;
                }

                // Store to rate desired variable for storing to UAVO
                rateDesiredAxis[i] =
                    bound(stabDesiredAxis[i], cast_struct_to_array(stabBank.ManualRate, stabBank.ManualRate.Roll)[i]);

                // Compute the inner loop
                actuatorDesiredAxis[i] = pid_apply_setpoint(&pids[PID_RATE_ROLL + i], speedScaleFactor, rateDesiredAxis[i], gyro_filtered[i], dT);
                actuatorDesiredAxis[i] = bound(actuatorDesiredAxis[i], 1.0f);

                break;

            case STABILIZATIONDESIRED_STABILIZATIONMODE_ATTITUDE:
                if (reinit) {
                    pids[PID_ROLL + i].iAccumulator = 0;
                    pids[PID_RATE_ROLL + i].iAccumulator = 0;
                }

                // Compute the outer loop
                rateDesiredAxis[i] = pid_apply(&pids[PID_ROLL + i], local_error[i], dT);
                rateDesiredAxis[i] = bound(rateDesiredAxis[i],
                                           cast_struct_to_array(stabBank.MaximumRate, stabBank.MaximumRate.Roll)[i]);

                // Compute the inner loop
                actuatorDesiredAxis[i] = pid_apply_setpoint(&pids[PID_RATE_ROLL + i], speedScaleFactor, rateDesiredAxis[i], gyro_filtered[i], dT);
                actuatorDesiredAxis[i] = bound(actuatorDesiredAxis[i], 1.0f);

                break;

            case STABILIZATIONDESIRED_STABILIZATIONMODE_RATTITUDE:
                // A parameterization from Attitude mode at center stick
                // - to Rate mode at full stick
                // This is done by parameterizing to use the rotation rate that Attitude mode
                // - would use at center stick to using the rotation rate that Rate mode
                // - would use at full stick in a weighted average sort of way.
            {
                if (reinit) {
                    pids[PID_ROLL + i].iAccumulator = 0;
                    pids[PID_RATE_ROLL + i].iAccumulator = 0;
                    pids[PID_RATEA_ROLL + i].iAccumulator = 0;
                }

                // Compute what Rate mode would give for this stick angle's rate
                // Save Rate's rate in a temp for later merging with Attitude's rate
                float rateDesiredAxisRate;
                rateDesiredAxisRate = bound(stabDesiredAxis[i], 1.0f)
                                      * cast_struct_to_array(stabBank.ManualRate, stabBank.ManualRate.Roll)[i];

                // Compute what Attitude mode would give for this stick angle's rate

                // stabDesired for this mode is [-1.0f,+1.0f]
                // - multiply by Attitude mode max angle to get desired angle
                // - subtract off the actual angle to get the angle error
                // This is what local_error[] holds for Attitude mode
                float attitude_error = stabDesiredAxis[i]
                                       * cast_struct_to_array(stabBank.RollMax, stabBank.RollMax)[i]
                                       - cast_struct_to_array(attitudeState.Roll, attitudeState.Roll)[i];

                // Compute the outer loop just like Attitude mode does
                float rateDesiredAxisAttitude;
                rateDesiredAxisAttitude = pid_apply(&pids[PID_ROLL + i], attitude_error, dT);
                rateDesiredAxisAttitude = bound(rateDesiredAxisAttitude,
                                                cast_struct_to_array(stabBank.MaximumRate,
                                                                     stabBank.MaximumRate.Roll)[i]);

                // Compute the weighted average rate desired
                // Using max() rather than sqrt() for cpu speed;
                // - this makes the stick region into a square;
                // - this is a feature!
                // - hold a roll angle and add just pitch without the stick sensitivity changing
                // magnitude = sqrt(stabDesired.Roll*stabDesired.Roll + stabDesired.Pitch*stabDesired.Pitch);
                float magnitude;
                magnitude = fmaxf(fabsf(stabDesired.Roll), fabsf(stabDesired.Pitch));
                rateDesiredAxis[i] = (1.0f - magnitude) * rateDesiredAxisAttitude
                                     + magnitude * rateDesiredAxisRate;

                // Compute the inner loop for both Rate mode and Attitude mode
                // actuatorDesiredAxis[i] is the weighted average of the two PIDs from the two rates
                actuatorDesiredAxis[i] =
                    (1.0f - magnitude) * pid_apply_setpoint(&pids[PID_RATEA_ROLL + i], speedScaleFactor, rateDesiredAxis[i], gyro_filtered[i], dT)
                    + magnitude * pid_apply_setpoint(&pids[PID_RATE_ROLL + i], speedScaleFactor, rateDesiredAxis[i], gyro_filtered[i], dT);
                actuatorDesiredAxis[i] = bound(actuatorDesiredAxis[i], 1.0f);

                // settings.RattitudeAntiWindup controls the iAccumulator zeroing
                // - so both iAccs don't wind up too far;
                // - nor do both iAccs get held too close to zero at mid stick

                // I suspect that there would be windup without it
                // - since rate and attitude fight each other here
                // - rate trying to pull it over the top and attitude trying to pull it back down

                // Wind-up increases linearly with cycles for a fixed error.
                // We must never increase the iAcc or we risk oscillation.

                // Use the powf() function to make two anti-windup curves
                // - one for zeroing rate close to center stick
                // - the other for zeroing attitude close to max stick

                // the bigger the dT      the more anti windup needed
                // the bigger the PID[].i the more anti windup needed
                // more anti windup is achieved with a lower powf() power
                // a doubling of e.g. PID[].i should cause the runtime anti windup factor
                // to get twice as far away from 1.0 (towards zero)
                // e.g. from .90 to .80

                // magic numbers
                // these generate the inverted parabola like curves that go through [0,1] and [1,0]
                // the higher the power, the closer the curve is to a straight line
                // from [0,1] to [1,1] to [1,0] and the less anti windup is applied

                // the UAVO RattitudeAntiWindup varies from 0 to 31
                // 0 turns off anti windup
                // 1 gives very little anti-windup because the power given to powf() is 31
                // 31 gives a lot of anti-windup because the power given to powf() is 1
                // the 32.1 is what does this
                // the 7.966 and 17.668 cancel the default PID value and dT given to log2f()
                // if these are non-default, tweaking is thus done so the user doesn't have to readjust
                // the default value of 10 for UAVO RattitudeAntiWindup gives a power of 22
                // these calculations are for magnitude = 0.5, so 22 corresponds to the number of bits
                // used in the mantissa of the float
                // i.e. 1.0-(0.5^22) almost underflows

                // This may only be useful for aircraft with large Ki values and limits
                if (dT > 0.0f && rattitude_anti_windup > 0.0f) {
                    float factor;

                    // At magnitudes close to one, the Attitude accumulators gets zeroed
                    if (pids[PID_ROLL + i].i > 0.0f) {
                        factor = 1.0f - stab_powf(magnitude, ((uint8_t)(32.1f - 7.966f - stab_log2f(dT * pids[PID_ROLL + i].i))) - rattitude_anti_windup);
                        pids[PID_ROLL + i].iAccumulator *= factor;
                    }
                    if (pids[PID_RATEA_ROLL + i].i > 0.0f) {
                        factor = 1.0f - stab_powf(magnitude, ((uint8_t)(32.1f - 17.668f - stab_log2f(dT * pids[PID_RATEA_ROLL + i].i))) - rattitude_anti_windup);
                        pids[PID_RATEA_ROLL + i].iAccumulator *= factor;
                    }

                    // At magnitudes close to zero, the Rate accumulator gets zeroed
                    if (pids[PID_RATE_ROLL + i].i > 0.0f) {
                        factor = 1.0f - stab_powf(1.0f - magnitude, ((uint8_t)(32.1f - 17.668f - stab_log2f(dT * pids[PID_RATE_ROLL + i].i))) - rattitude_anti_windup);
                        pids[PID_RATE_ROLL + i].iAccumulator *= factor;
                    }
                }

                break;
            }

            case STABILIZATIONDESIRED_STABILIZATIONMODE_VIRTUALBAR:

                // Store for debugging output
                rateDesiredAxis[i] = stabDesiredAxis[i];

                // Run a virtual flybar stabilization algorithm on this axis
                stabilization_virtual_flybar(gyro_filtered[i], rateDesiredAxis[i], &actuatorDesiredAxis[i], dT, reinit, i, &settings);

                break;

            case STABILIZATIONDESIRED_STABILIZATIONMODE_WEAKLEVELING:
                // FIXME: local_error[] is rate - attitude for Weak Leveling
                // The only ramifications are:
                // Weak Leveling Kp is off by a factor of 3 to 12 and may need a different default in GCS
                // Changing Rate mode max rate currently requires a change to Kp
                // That would be changed to Attitude mode max angle affecting Kp
                // Also does not take dT into account
            {
                if (reinit) {
                    pids[PID_RATE_ROLL + i].iAccumulator = 0;
                }

                float weak_leveling = local_error[i] * weak_leveling_kp;
                weak_leveling = bound(weak_leveling, weak_leveling_max);

                // Compute desired rate as input biased towards leveling
                rateDesiredAxis[i]     = stabDesiredAxis[i] + weak_leveling;
                actuatorDesiredAxis[i] = pid_apply_setpoint(&pids[PID_RATE_ROLL + i], speedScaleFactor, rateDesiredAxis[i], gyro_filtered[i], dT);
                actuatorDesiredAxis[i] = bound(actuatorDesiredAxis[i], 1.0f);

                break;
            }

            case STABILIZATIONDESIRED_STABILIZATIONMODE_AXISLOCK:
                if (reinit) {
                    pids[PID_RATE_ROLL + i].iAccumulator = 0;
                }

                if (fabsf(stabDesiredAxis[i]) > max_axislock_rate) {
                    // While getting strong commands act like rate mode
                    rateDesiredAxis[i] = stabDesiredAxis[i];
                    axis_lock_accum[i] = 0;
                } else {
                    // For weaker commands or no command simply attitude lock (almost) on no gyro change
                    axis_lock_accum[i] += (stabDesiredAxis[i] - gyro_filtered[i]) * dT;
                    axis_lock_accum[i]  = bound(axis_lock_accum[i], max_axis_lock);
                    rateDesiredAxis[i]  = pid_apply(&pids[PID_ROLL + i], axis_lock_accum[i], dT);
                }

                rateDesiredAxis[i]     = bound(rateDesiredAxis[i],
                                               cast_struct_to_array(stabBank.ManualRate, stabBank.ManualRate.Roll)[i]);

                actuatorDesiredAxis[i] = pid_apply_setpoint(&pids[PID_RATE_ROLL + i], speedScaleFactor, rateDesiredAxis[i], gyro_filtered[i], dT);
                actuatorDesiredAxis[i] = bound(actuatorDesiredAxis[i], 1.0f);

                break;

            case STABILIZATIONDESIRED_STABILIZATIONMODE_RELAYRATE:
                // Store to rate desired variable for storing to UAVO
                rateDesiredAxis[i] = bound(stabDesiredAxis[i],
                                           cast_struct_to_array(stabBank.ManualRate, stabBank.ManualRate.Roll)[i]);

                // Run the relay controller which also estimates the oscillation parameters
                stabilization_relay_rate(rateDesiredAxis[i] - gyro_filtered[i], &actuatorDesiredAxis[i], i, reinit);
                actuatorDesiredAxis[i] = bound(actuatorDesiredAxis[i], 1.0f);

                break;

            case STABILIZATIONDESIRED_STABILIZATIONMODE_RELAYATTITUDE:
                if (reinit) {
                    pids[PID_ROLL + i].iAccumulator = 0;
                }

                // Compute the outer loop like attitude mode
                rateDesiredAxis[i] = pid_apply(&pids[PID_ROLL + i], local_error[i], dT);
                rateDesiredAxis[i] = bound(rateDesiredAxis[i],
                                           cast_struct_to_array(stabBank.MaximumRate, stabBank.MaximumRate.Roll)[i]);

                // Run the relay controller which also estimates the oscillation parameters
                stabilization_relay_rate(rateDesiredAxis[i] - gyro_filtered[i], &actuatorDesiredAxis[i], i, reinit);
                actuatorDesiredAxis[i] = bound(actuatorDesiredAxis[i], 1.0f);

                break;

            case STABILIZATIONDESIRED_STABILIZATIONMODE_NONE:
                actuatorDesiredAxis[i] = bound(stabDesiredAxis[i], 1.0f);
                break;
            default:
                error = true;
                break;
            }
        }

        if (settings.VbarPiroComp == STABILIZATIONSETTINGS_VBARPIROCOMP_TRUE) {
            stabilization_virtual_flybar_pirocomp(gyro_filtered[2], dT);
        }

#ifdef DIAG_RATEDESIRED
        RateDesiredSet(&rateDesired);
#endif

        // Save dT
        actuatorDesired.UpdateTime = dT * 1000;
        actuatorDesired.Throttle   = stabDesired.Throttle;

        // Suppress desired output while disarmed or throttle low, for configured axis
        if (flightStatus.Armed != FLIGHTSTATUS_ARMED_ARMED || stabDesired.Throttle < 0) {
            if (lowThrottleZeroAxis[ROLL]) {
                actuatorDesired.Roll = 0.0f;
            }

            if (lowThrottleZeroAxis[PITCH]) {
                actuatorDesired.Pitch = 0.0f;
            }

            if (lowThrottleZeroAxis[YAW]) {
                actuatorDesired.Yaw = 0.0f;
            }
        }

        // modify throttle according to 1/cos(bank angle)
        // to maintain same altitdue with changing bank angle
        // but without manually adjusting throttle
        // do it here and all the various flight modes (e.g. Altitude Hold) can use it
        if (flight_mode_switch_position < NUM_FMS_POSITIONS
            && cruise_control_flight_mode_switch_pos_enable[flight_mode_switch_position] != (uint8_t)0
            && cruise_control_max_power_factor > 0.0001f) {
            static uint8_t toggle;
            static float factor;
            float angle;
            // get attitude state and calculate angle
            // do it every 8th iteration to save CPU
            if ((toggle++ & 7) == 0) {
                // spherical right triangle
                // 0 <= acosf() <= Pi
                angle = RAD2DEG(acosf(cos_lookup_deg(attitudeState.Roll) * cos_lookup_deg(attitudeState.Pitch)));
                // if past the cutoff angle (60 to 180 (180 means never))
                if (angle > cruise_control_max_angle) {
                    // -1 reversed collective, 0 zero power, or 1 normal power
                    // these are all unboosted
                    factor = cruise_control_inverted_power_switch;
                } else {
                    // avoid singularity
                    if (angle > 89.999f && angle < 90.001f) {
                        factor = cruise_control_max_power_factor;
                    } else {
                        factor = 1.0f / fabsf(cos_lookup_deg(angle));
                        if (factor > cruise_control_max_power_factor) {
                            factor = cruise_control_max_power_factor;
                        }
                    }
                    // factor in the power trim, no effect at 1.0, linear effect increases with factor
                    factor = (factor - 1.0f) * cruise_control_power_trim + 1.0f;
                    // if inverted and they want negative boost
                    if (angle > 90.0f && cruise_control_inverted_power_switch == (int8_t)-1) {
                        factor = -factor;
                        // as long as throttle is getting reversed
                        // we may as well do pitch and yaw for a complete "invert switch"
                        actuatorDesired.Pitch = -actuatorDesired.Pitch;
                        actuatorDesired.Yaw   = -actuatorDesired.Yaw;
                    }
                }
            }

            // also don't adjust throttle if <= 0, leaves neg alone and zero throttle stops motors
            if (actuatorDesired.Throttle > cruise_control_min_throttle) {
                // quad    example factor of 2 at hover power of 40%: (0.4 - 0.0) * 2.0 + 0.0 = 0.8
                // CP heli example factor of 2 at hover stick of 60%: (0.6 - 0.5) * 2.0 + 0.5 = 0.7
                actuatorDesired.Throttle = (actuatorDesired.Throttle - cruise_control_neutral_thrust) * factor + cruise_control_neutral_thrust;
                if (actuatorDesired.Throttle > cruise_control_max_throttle) {
                    actuatorDesired.Throttle = cruise_control_max_throttle;
                } else if (actuatorDesired.Throttle < cruise_control_min_throttle) {
                    actuatorDesired.Throttle = cruise_control_min_throttle;
                }
            }
        }

        if (PARSE_FLIGHT_MODE(flightStatus.FlightMode) != FLIGHTMODE_MANUAL) {
            ActuatorDesiredSet(&actuatorDesired);
        } else {
            // Force all axes to reinitialize when engaged
            for (uint8_t i = 0; i < MAX_AXES; i++) {
                previous_mode[i] = 255;
            }
        }

        if (flightStatus.Armed != FLIGHTSTATUS_ARMED_ARMED ||
            (lowThrottleZeroIntegral && stabDesired.Throttle < 0)) {
            // Force all axes to reinitialize when engaged
            for (uint8_t i = 0; i < MAX_AXES; i++) {
                previous_mode[i] = 255;
            }
        }

        // Clear or set alarms.  Done like this to prevent toggline each cycle
        // and hammering system alarms
        if (error) {
            AlarmsSet(SYSTEMALARMS_ALARM_STABILIZATION, SYSTEMALARMS_ALARM_ERROR);
        } else {
            AlarmsClear(SYSTEMALARMS_ALARM_STABILIZATION);
        }
    }
}


/**
 * Clear the accumulators and derivatives for all the axes
 */
static void ZeroPids(void)
{
    for (uint32_t i = 0; i < PID_MAX; i++) {
        pid_zero(&pids[i]);
    }


    for (uint8_t i = 0; i < 3; i++) {
        axis_lock_accum[i] = 0.0f;
    }
}


/**
 * Bound input value between limits
 */
static float bound(float val, float range)
{
    if (val < -range) {
        return -range;
    } else if (val > range) {
        return range;
    }
    return val;
}


// x small (0.0 < x < .01) so interpolation of fractional part is reasonable
static float stab_log2f(float x)
{
    union {
        volatile float    f;
        volatile uint32_t i;
        volatile unsigned char c[4];
    } __attribute__((packed)) u1, u2;

    u2.f   = u1.f = x;
    u1.i <<= 1;
    u2.i  &= 0xff800000;

    // get and unbias the exponent, add in a linear interpolation of the fractional part
    return (float)(u1.c[3] - 127) + (x / u2.f) - 1.0f;
}


// 0<=x<=1, 0<=p<=31
static float stab_powf(float x, uint8_t p)
{
    float retval = 1.0f;

    while (p) {
        if (p & 1) {
            retval *= x;
        }
        x  *= x;
        p >>= 1;
    }

    return retval;
}


static void SettingsBankUpdatedCb(__attribute__((unused)) UAVObjEvent *ev)
{
    StabilizationBankData bank, oldBank;

    StabilizationBankGet(&oldBank);

    if (cur_flight_mode < 0 || cur_flight_mode >= NUM_FMS_POSITIONS) {
        return;
    }

    switch (settings.FlightModeMap[cur_flight_mode]) {
    case 0:
        StabilizationSettingsBank1Get((StabilizationSettingsBank1Data *)&bank);
        break;

    case 1:
        StabilizationSettingsBank2Get((StabilizationSettingsBank2Data *)&bank);
        break;

    case 2:
        StabilizationSettingsBank3Get((StabilizationSettingsBank3Data *)&bank);
        break;

    default:
        memset(&bank, 0, sizeof(StabilizationBankDataPacked));
// return; //bank number is invalid. All we can do is ignore it.
    }

    // Need to do this to prevent an infinite loop
    if (memcmp(&oldBank, &bank, sizeof(StabilizationBankDataPacked)) != 0) {
        StabilizationBankSet(&bank);
    }
}

static void BankUpdatedCb(__attribute__((unused)) UAVObjEvent *ev)
{
    StabilizationBankData bank;

    StabilizationBankGet(&bank);

// this code will be needed if any other modules alter stabilizationbank
/*
    StabilizationBankData curBank;
    if(flight_mode < 0) return;

    switch(cast_struct_to_array(settings.FlightModeMap, settings.FlightModeMap.Stabilized1)[flight_mode])
    {
    case 0:
        StabilizationSettingsBank1Get((StabilizationSettingsBank1Data *) &curBank);
        if(memcmp(&curBank, &bank, sizeof(StabilizationBankDataPacked)) != 0)
        {
            StabilizationSettingsBank1Set((StabilizationSettingsBank1Data *) &bank);
        }
        break;

    case 1:
        StabilizationSettingsBank2Get((StabilizationSettingsBank2Data *) &curBank);
        if(memcmp(&curBank, &bank, sizeof(StabilizationBankDataPacked)) != 0)
        {
            StabilizationSettingsBank2Set((StabilizationSettingsBank2Data *) &bank);
        }
        break;

    case 2:
        StabilizationSettingsBank3Get((StabilizationSettingsBank3Data *) &curBank);
        if(memcmp(&curBank, &bank, sizeof(StabilizationBankDataPacked)) != 0)
        {
            StabilizationSettingsBank3Set((StabilizationSettingsBank3Data *) &bank);
        }
        break;

    default:
        return; //invalid bank number
    }
 */


    // Set the roll rate PID constants
    pid_configure(&pids[PID_RATE_ROLL], bank.RollRatePID.Kp,
                  bank.RollRatePID.Ki,
                  bank.RollRatePID.Kd,
                  bank.RollRatePID.ILimit);

    // Set the pitch rate PID constants
    pid_configure(&pids[PID_RATE_PITCH], bank.PitchRatePID.Kp,
                  bank.PitchRatePID.Ki,
                  bank.PitchRatePID.Kd,
                  bank.PitchRatePID.ILimit);

    // Set the yaw rate PID constants
    pid_configure(&pids[PID_RATE_YAW], bank.YawRatePID.Kp,
                  bank.YawRatePID.Ki,
                  bank.YawRatePID.Kd,
                  bank.YawRatePID.ILimit);

    // Set the roll attitude PI constants
    pid_configure(&pids[PID_ROLL], bank.RollPI.Kp,
                  bank.RollPI.Ki,
                  0,
                  bank.RollPI.ILimit);

    // Set the pitch attitude PI constants
    pid_configure(&pids[PID_PITCH], bank.PitchPI.Kp,
                  bank.PitchPI.Ki,
                  0,
                  bank.PitchPI.ILimit);

    // Set the yaw attitude PI constants
    pid_configure(&pids[PID_YAW], bank.YawPI.Kp,
                  bank.YawPI.Ki,
                  0,
                  bank.YawPI.ILimit);

    // Set the Rattitude roll rate PID constants
    pid_configure(&pids[PID_RATEA_ROLL],
                  bank.RollRatePID.Kp,
                  bank.RollRatePID.Ki,
                  bank.RollRatePID.Kd,
                  bank.RollRatePID.ILimit);

    // Set the Rattitude pitch rate PID constants
    pid_configure(&pids[PID_RATEA_PITCH],
                  bank.PitchRatePID.Kp,
                  bank.PitchRatePID.Ki,
                  bank.PitchRatePID.Kd,
                  bank.PitchRatePID.ILimit);

    // Set the Rattitude yaw rate PID constants
    pid_configure(&pids[PID_RATEA_YAW],
                  bank.YawRatePID.Kp,
                  bank.YawRatePID.Ki,
                  bank.YawRatePID.Kd,
                  bank.YawRatePID.ILimit);
}


static void SettingsUpdatedCb(__attribute__((unused)) UAVObjEvent *ev)
{
    StabilizationSettingsGet(&settings);

    // Set up the derivative term
    pid_configure_derivative(settings.DerivativeCutoff, settings.DerivativeGamma);

    // Maximum deviation to accumulate for axis lock
    max_axis_lock     = settings.MaxAxisLock;
    max_axislock_rate = settings.MaxAxisLockRate;

    // Settings for weak leveling
    weak_leveling_kp  = settings.WeakLevelingKp;
    weak_leveling_max = settings.MaxWeakLevelingRate;

    // Whether to zero the PID integrals while throttle is low
    lowThrottleZeroIntegral    = settings.LowThrottleZeroIntegral == STABILIZATIONSETTINGS_LOWTHROTTLEZEROINTEGRAL_TRUE;

    // Whether to suppress (zero) the StabilizationDesired output for each axis while disarmed or throttle is low
    lowThrottleZeroAxis[ROLL]  = settings.LowThrottleZeroAxis.Roll == STABILIZATIONSETTINGS_LOWTHROTTLEZEROAXIS_TRUE;
    lowThrottleZeroAxis[PITCH] = settings.LowThrottleZeroAxis.Pitch == STABILIZATIONSETTINGS_LOWTHROTTLEZEROAXIS_TRUE;
    lowThrottleZeroAxis[YAW]   = settings.LowThrottleZeroAxis.Yaw == STABILIZATIONSETTINGS_LOWTHROTTLEZEROAXIS_TRUE;

    // The dT has some jitter iteration to iteration that we don't want to
    // make thie result unpredictable.  Still, it's nicer to specify the constant
    // based on a time (in ms) rather than a fixed multiplier.  The error between
    // update rates on OP (~300 Hz) and CC (~475 Hz) is negligible for this
    // calculation
    const float fakeDt = 0.0025f;
    if (settings.GyroTau < 0.0001f) {
        gyro_alpha = 0; // not trusting this to resolve to 0
    } else {
        gyro_alpha = expf(-fakeDt / settings.GyroTau);
    }

    // Compute time constant for vbar decay term based on a tau
    vbar_decay = expf(-fakeDt / settings.VbarTau);

    // force flight mode update
    cur_flight_mode = -1;

    // Rattitude flight mode anti-windup factor
    rattitude_anti_windup = settings.RattitudeAntiWindup;

    cruise_control_min_throttle     = (float)settings.CruiseControlMinThrottle / 100.0f;
    cruise_control_max_throttle     = (float)settings.CruiseControlMaxThrottle / 100.0f;
    cruise_control_max_angle        = settings.CruiseControlMaxAngle;
    cruise_control_max_power_factor = settings.CruiseControlMaxPowerFactor;
    cruise_control_power_trim       = settings.CruiseControlPowerTrim / 100.0f;
    cruise_control_inverted_power_switch = settings.CruiseControlInvertedPowerSwitch;
    cruise_control_neutral_thrust   = (float)settings.CruiseControlNeutralThrust / 100.0f;

    memcpy(
        cruise_control_flight_mode_switch_pos_enable,
        settings.CruiseControlFlightModeSwitchPosEnable,
        sizeof(cruise_control_flight_mode_switch_pos_enable));
}

/**
 * @}
 * @}
 */