ardupilot/libraries/APO/AP_CommLink.cpp

/*
 * AP_CommLink.cpp
 *
 *  Created on: Apr 30, 2011
 *      Author: jgoppert
 */

#include "../FastSerial/FastSerial.h"
#include "AP_CommLink.h"
#include "AP_Navigator.h"
#include "AP_Guide.h"
#include "AP_Controller.h"
#include "AP_MavlinkCommand.h"
#include "AP_HardwareAbstractionLayer.h"
#include "AP_RcChannel.h"
#include "../AP_GPS/AP_GPS.h"
#include "../AP_Math/AP_Math.h"
#include "../AP_IMU/AP_IMU.h"
#include "../AP_Compass/AP_Compass.h"
#include "AP_BatteryMonitor.h"

namespace apo {

uint8_t MavlinkComm::_nChannels = 0;
uint8_t MavlinkComm::_paramNameLengthMax = 13;

AP_CommLink::AP_CommLink(FastSerial * link, AP_Navigator * navigator, AP_Guide * guide,
                         AP_Controller * controller, AP_HardwareAbstractionLayer * hal) :
    _link(link), _navigator(navigator), _guide(guide),
    _controller(controller), _hal(hal) {
}

MavlinkComm::MavlinkComm(FastSerial * link, AP_Navigator * nav, AP_Guide * guide,
                         AP_Controller * controller, AP_HardwareAbstractionLayer * hal) :
    AP_CommLink(link, nav, guide, controller, hal),

    // options
    _useRelativeAlt(true),

    // commands
    _sendingCmds(false), _receivingCmds(false),
    _cmdTimeLastSent(millis()), _cmdTimeLastReceived(millis()),
    _cmdDestSysId(0), _cmdDestCompId(0), _cmdRequestIndex(0),
    _cmdMax(30), _cmdNumberRequested(0),

    // parameters
    _parameterCount(0), _queuedParameter(NULL),
    _queuedParameterIndex(0) {

    switch (_nChannels) {
    case 0:
        mavlink_comm_0_port = link;
        _channel = MAVLINK_COMM_0;
        _nChannels++;
        break;
    case 1:
        mavlink_comm_1_port = link;
        _channel = MAVLINK_COMM_1;
        _nChannels++;
        break;
    default:
        // signal that number of channels exceeded
        _channel = MAVLINK_COMM_3;
        break;
    }
}

void MavlinkComm::send() {
    // if number of channels exceeded return
    if (_channel == MAVLINK_COMM_3)
        return;
}

void MavlinkComm::sendMessage(uint8_t id, uint32_t param) {
    //_hal->debug->printf_P(PSTR("send message\n"));

    // if number of channels exceeded return
    if (_channel == MAVLINK_COMM_3)
        return;

    uint64_t timeStamp = micros();

    switch (id) {

    case MAVLINK_MSG_ID_HEARTBEAT: {
        mavlink_msg_heartbeat_send(_channel, mavlink_system.type,
                                   MAV_AUTOPILOT_ARDUPILOTMEGA);
        break;
    }

    case MAVLINK_MSG_ID_ATTITUDE: {
        mavlink_msg_attitude_send(_channel, timeStamp,
                                  _navigator->getRoll(), _navigator->getPitch(),
                                  _navigator->getYaw(), _navigator->getRollRate(),
                                  _navigator->getPitchRate(), _navigator->getYawRate());
        break;
    }

    case MAVLINK_MSG_ID_GLOBAL_POSITION: {
        mavlink_msg_global_position_send(_channel, timeStamp,
                                         _navigator->getLat() * rad2Deg,
                                         _navigator->getLon() * rad2Deg, _navigator->getAlt(),
                                         _navigator->getVN(), _navigator->getVE(),
                                         _navigator->getVD());
        break;
    }

    case MAVLINK_MSG_ID_LOCAL_POSITION: {
        mavlink_msg_local_position_send(_channel, timeStamp,
                _navigator->getPN(),_navigator->getPE(), _navigator->getPD(),
                _navigator->getVN(), _navigator->getVE(), _navigator->getVD());
        break;
    }

    case MAVLINK_MSG_ID_GPS_RAW: {
        mavlink_msg_gps_raw_send(_channel, timeStamp, _hal->gps->status(),
                                 _navigator->getLat() * rad2Deg,
                                 _navigator->getLon() * rad2Deg, _navigator->getAlt(), 0, 0,
                                 _navigator->getGroundSpeed()*1000.0,
                                 _navigator->getYaw() * rad2Deg);
        break;
    }

    /*
     case MAVLINK_MSG_ID_GPS_RAW_INT: {
     mavlink_msg_gps_raw_int_send(_channel,timeStamp,_hal->gps->status(),
     _navigator->getLat_degInt(), _navigator->getLon_degInt(),_navigator->getAlt_intM(), 0,0,
     _navigator->getGroundSpeed(),_navigator->getYaw()*rad2Deg);
     break;
     }
     */

    case MAVLINK_MSG_ID_SCALED_IMU: {
        int16_t xmag, ymag, zmag;
        xmag = ymag = zmag = 0;
        if (_hal->compass) {
            // XXX THIS IS NOT SCALED
            xmag = _hal->compass->mag_x;
            ymag = _hal->compass->mag_y;
            zmag = _hal->compass->mag_z;
        }
        mavlink_msg_scaled_imu_send(_channel, timeStamp,
            _navigator->getXAccel()*1e3,
            _navigator->getYAccel()*1e3,
            _navigator->getZAccel()*1e3,
            _navigator->getRollRate()*1e3,
            _navigator->getPitchRate()*1e3,
            _navigator->getYawRate()*1e3,
            xmag, ymag, zmag);
        break;
    }

    case MAVLINK_MSG_ID_RC_CHANNELS_SCALED: {
        int16_t ch[8];
        for (int i = 0; i < 8; i++)
            ch[i] = 0;
        for (uint8_t i = 0; i < 8 && i < _hal->rc.getSize(); i++) {
            ch[i] = 10000 * _hal->rc[i]->getPosition();
            //_hal->debug->printf_P(PSTR("ch: %d position: %d\n"),i,ch[i]);
        }
        mavlink_msg_rc_channels_scaled_send(_channel, ch[0], ch[1], ch[2],
                                            ch[3], ch[4], ch[5], ch[6], ch[7], 255);
        break;
    }

    case MAVLINK_MSG_ID_RC_CHANNELS_RAW: {
        int16_t ch[8];
        for (int i = 0; i < 8; i++)
            ch[i] = 0;
        for (uint8_t i = 0; i < 8 && i < _hal->rc.getSize(); i++)
            ch[i] = _hal->rc[i]->getPwm();
        mavlink_msg_rc_channels_raw_send(_channel, ch[0], ch[1], ch[2],
                                         ch[3], ch[4], ch[5], ch[6], ch[7], 255);
        break;
    }

    case MAVLINK_MSG_ID_SYS_STATUS: {

        uint16_t batteryVoltage = 0; // (milli volts)
        uint16_t batteryPercentage = 1000; // times 10
        if (_hal->batteryMonitor) {
            batteryPercentage = _hal->batteryMonitor->getPercentage()*10;
            batteryVoltage = _hal->batteryMonitor->getVoltage()*1000;
        }
        mavlink_msg_sys_status_send(_channel, _controller->getMode(),
                                    _guide->getMode(), _hal->getState(), _hal->load * 10,
                                    batteryVoltage, batteryPercentage, _packetDrops);
        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT_ACK: {
        sendText(SEVERITY_LOW, PSTR("waypoint ack"));
        //mavlink_waypoint_ack_t packet;
        uint8_t type = 0; // ok (0), error(1)
        mavlink_msg_waypoint_ack_send(_channel, _cmdDestSysId,
                                      _cmdDestCompId, type);

        // turn off waypoint send
        _receivingCmds = false;
        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT_CURRENT: {
        mavlink_msg_waypoint_current_send(_channel,
                                          _guide->getCurrentIndex());
        break;
    }

    default: {
        char msg[50];
        sprintf(msg, "autopilot sending unknown command with id: %d", id);
        sendText(SEVERITY_HIGH, msg);
    }

    } // switch
} // send message

void MavlinkComm::receive() {
    //_hal->debug->printf_P(PSTR("receive\n"));
    // if number of channels exceeded return
    //
    if (_channel == MAVLINK_COMM_3)
        return;

    // receive new packets
    mavlink_message_t msg;
    mavlink_status_t status;
    status.packet_rx_drop_count = 0;

    // process received bytes
    while (comm_get_available(_channel)) {
        uint8_t c = comm_receive_ch(_channel);

        // Try to get a new message
        if (mavlink_parse_char(_channel, c, &msg, &status))
            _handleMessage(&msg);
    }

    // Update packet drops counter
    _packetDrops += status.packet_rx_drop_count;
}

void MavlinkComm::sendText(uint8_t severity, const char *str) {
    mavlink_msg_statustext_send(_channel, severity, (const int8_t*) str);
}

void MavlinkComm::sendText(uint8_t severity, const prog_char_t *str) {
    mavlink_statustext_t m;
    uint8_t i;
    for (i = 0; i < sizeof(m.text); i++) {
        m.text[i] = pgm_read_byte((const prog_char *) (str++));
    }
    if (i < sizeof(m.text))
        m.text[i] = 0;
    sendText(severity, (const char *) m.text);
}

void MavlinkComm::acknowledge(uint8_t id, uint8_t sum1, uint8_t sum2) {
}

/**
 * sends parameters one at a time
 */
void MavlinkComm::sendParameters() {
    //_hal->debug->printf_P(PSTR("send parameters\n"));
    // Check to see if we are sending parameters
    while (NULL != _queuedParameter) {
        AP_Var *vp;
        float value;

        // copy the current parameter and prepare to move to the next
        vp = _queuedParameter;
        _queuedParameter = _queuedParameter->next();

        // if the parameter can be cast to float, report it here and break out of the loop
        value = vp->cast_to_float();
        if (!isnan(value)) {

            char paramName[_paramNameLengthMax];
            vp->copy_name(paramName, sizeof(paramName));

            mavlink_msg_param_value_send(_channel, (int8_t*) paramName,
                                         value, _countParameters(), _queuedParameterIndex);

            _queuedParameterIndex++;
            break;
        }
    }

}

/**
 * request commands one at a time
 */
void MavlinkComm::requestCmds() {
    //_hal->debug->printf_P(PSTR("requesting commands\n"));
    // request cmds one by one
    if (_receivingCmds && _cmdRequestIndex <= _cmdNumberRequested) {
        mavlink_msg_waypoint_request_send(_channel, _cmdDestSysId,
                                          _cmdDestCompId, _cmdRequestIndex);
    }
}

void MavlinkComm::_handleMessage(mavlink_message_t * msg) {

    uint32_t timeStamp = micros();

    switch (msg->msgid) {
        _hal->debug->printf_P(PSTR("message received: %d"), msg->msgid);

    case MAVLINK_MSG_ID_HEARTBEAT: {
        mavlink_heartbeat_t packet;
        mavlink_msg_heartbeat_decode(msg, &packet);
        _hal->lastHeartBeat = micros();
        break;
    }

    case MAVLINK_MSG_ID_GPS_RAW: {
        // decode
        mavlink_gps_raw_t packet;
        mavlink_msg_gps_raw_decode(msg, &packet);

        _navigator->setTimeStamp(timeStamp);
        _navigator->setLat(packet.lat * deg2Rad);
        _navigator->setLon(packet.lon * deg2Rad);
        _navigator->setAlt(packet.alt);
        _navigator->setYaw(packet.hdg * deg2Rad);
        _navigator->setGroundSpeed(packet.v);
        _navigator->setAirSpeed(packet.v);
        //_hal->debug->printf_P(PSTR("received hil gps raw packet\n"));
        /*
         _hal->debug->printf_P(PSTR("received lat: %f deg\tlon: %f deg\talt: %f m\n"),
         packet.lat,
         packet.lon,
         packet.alt);
         */
        break;
    }

    case MAVLINK_MSG_ID_HIL_STATE: {
        // decode
        mavlink_hil_state_t packet;
        mavlink_msg_hil_state_decode(msg, &packet);
        _navigator->setTimeStamp(timeStamp);
        _navigator->setRoll(packet.roll);
        _navigator->setPitch(packet.pitch);
        _navigator->setYaw(packet.yaw);
        _navigator->setRollRate(packet.rollspeed);
        _navigator->setPitchRate(packet.pitchspeed);
        _navigator->setYawRate(packet.yawspeed);
        _navigator->setVN(packet.vx/ 1e2);
        _navigator->setVE(packet.vy/ 1e2);
        _navigator->setVD(packet.vz/ 1e2);
        _navigator->setLat_degInt(packet.lat);
        _navigator->setLon_degInt(packet.lon);
        _navigator->setAlt(packet.alt / 1e3);
        _navigator->setXAccel(packet.xacc/ 1e3);
        _navigator->setYAccel(packet.xacc/ 1e3);
        _navigator->setZAccel(packet.xacc/ 1e3);
        break; 
    } 

    case MAVLINK_MSG_ID_ATTITUDE: {
        // decode
        mavlink_attitude_t packet;
        mavlink_msg_attitude_decode(msg, &packet);

        // set dcm hil sensor
        _navigator->setTimeStamp(timeStamp);
        _navigator->setRoll(packet.roll);
        _navigator->setPitch(packet.pitch);
        _navigator->setYaw(packet.yaw);
        _navigator->setRollRate(packet.rollspeed);
        _navigator->setPitchRate(packet.pitchspeed);
        _navigator->setYawRate(packet.yawspeed);
        //_hal->debug->printf_P(PSTR("received hil attitude packet\n"));
        break;
    }

    case MAVLINK_MSG_ID_ACTION: {
        // decode
        mavlink_action_t packet;
        mavlink_msg_action_decode(msg, &packet);
        if (_checkTarget(packet.target, packet.target_component))
            break;

        // do action
        sendText(SEVERITY_LOW, PSTR("action received"));
        switch (packet.action) {

        case MAV_ACTION_STORAGE_READ:
            AP_Var::load_all();
            break;

        case MAV_ACTION_STORAGE_WRITE:
            AP_Var::save_all();
            break;

        case MAV_ACTION_MOTORS_START:
            _hal->setState(MAV_STATE_ACTIVE);
            break;

        case MAV_ACTION_CALIBRATE_GYRO:
        case MAV_ACTION_CALIBRATE_MAG:
        case MAV_ACTION_CALIBRATE_ACC:
        case MAV_ACTION_CALIBRATE_PRESSURE:
            _hal->setState(MAV_STATE_STANDBY);
            _navigator->calibrate();
            break;

        case MAV_ACTION_EMCY_KILL:
        case MAV_ACTION_CONFIRM_KILL:
        case MAV_ACTION_MOTORS_STOP:
        case MAV_ACTION_SHUTDOWN:
            _hal->setState(MAV_STATE_STANDBY);
            _controller->setMode(MAV_MODE_LOCKED);
            break;

        case MAV_ACTION_LAUNCH:
        case MAV_ACTION_TAKEOFF:
            _controller->setMode(MAV_MODE_AUTO);
            _guide->setMode(MAV_NAV_LIFTOFF);
            break;

        case MAV_ACTION_LAND:
            _guide->setCurrentIndex(0);
            _guide->setMode(MAV_NAV_LANDING);
            break;

        case MAV_ACTION_EMCY_LAND:
            _guide->setMode(MAV_NAV_LANDING);
            break;

        case MAV_ACTION_LOITER:
        case MAV_ACTION_HALT:
            _guide->setMode(MAV_NAV_LOITER);
            break;

        case MAV_ACTION_SET_AUTO:
            _controller->setMode(MAV_MODE_AUTO);
            break;

        case MAV_ACTION_SET_MANUAL:
            _controller->setMode(MAV_MODE_MANUAL);
            break;

        case MAV_ACTION_RETURN:
            _guide->setMode(MAV_NAV_RETURNING);
            break;

        case MAV_ACTION_NAVIGATE:
        case MAV_ACTION_CONTINUE:
            _guide->setMode(MAV_NAV_WAYPOINT);
            break;

        case MAV_ACTION_CALIBRATE_RC:
        case MAV_ACTION_REBOOT:
        case MAV_ACTION_REC_START:
        case MAV_ACTION_REC_PAUSE:
        case MAV_ACTION_REC_STOP:
            sendText(SEVERITY_LOW, PSTR("action not implemented"));
            break;
        default:
            sendText(SEVERITY_LOW, PSTR("unknown action"));
            break;
        }
        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT_REQUEST_LIST: {
        sendText(SEVERITY_LOW, PSTR("waypoint request list"));

        // decode
        mavlink_waypoint_request_list_t packet;
        mavlink_msg_waypoint_request_list_decode(msg, &packet);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        // Start sending waypoints
        mavlink_msg_waypoint_count_send(_channel, msg->sysid, msg->compid,
                                        _guide->getNumberOfCommands());

        _cmdTimeLastSent = millis();
        _cmdTimeLastReceived = millis();
        _sendingCmds = true;
        _receivingCmds = false;
        _cmdDestSysId = msg->sysid;
        _cmdDestCompId = msg->compid;
        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT_REQUEST: {
        sendText(SEVERITY_LOW, PSTR("waypoint request"));

        // Check if sending waypiont
        if (!_sendingCmds)
            break;

        // decode
        mavlink_waypoint_request_t packet;
        mavlink_msg_waypoint_request_decode(msg, &packet);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        _hal->debug->printf_P(PSTR("sequence: %d\n"),packet.seq);
        AP_MavlinkCommand cmd(packet.seq);

        mavlink_waypoint_t wp = cmd.convert(_guide->getCurrentIndex());
        mavlink_msg_waypoint_send(_channel, _cmdDestSysId, _cmdDestCompId,
                                  wp.seq, wp.frame, wp.command, wp.current, wp.autocontinue,
                                  wp.param1, wp.param2, wp.param3, wp.param4, wp.x, wp.y,
                                  wp.z);

        // update last waypoint comm stamp
        _cmdTimeLastSent = millis();
        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT_ACK: {
        sendText(SEVERITY_LOW, PSTR("waypoint ack"));

        // decode
        mavlink_waypoint_ack_t packet;
        mavlink_msg_waypoint_ack_decode(msg, &packet);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        // check for error
        //uint8_t type = packet.type; // ok (0), error(1)

        // turn off waypoint send
        _sendingCmds = false;
        break;
    }

    case MAVLINK_MSG_ID_PARAM_REQUEST_LIST: {
        sendText(SEVERITY_LOW, PSTR("param request list"));

        // decode
        mavlink_param_request_list_t packet;
        mavlink_msg_param_request_list_decode(msg, &packet);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        // Start sending parameters - next call to ::update will kick the first one out

        _queuedParameter = AP_Var::first();
        _queuedParameterIndex = 0;
        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT_CLEAR_ALL: {
        sendText(SEVERITY_LOW, PSTR("waypoint clear all"));

        // decode
        mavlink_waypoint_clear_all_t packet;
        mavlink_msg_waypoint_clear_all_decode(msg, &packet);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        // clear all waypoints
        uint8_t type = 0; // ok (0), error(1)
        _guide->setNumberOfCommands(1);
        _guide->setCurrentIndex(0);

        // send acknowledgement 3 times to makes sure it is received
        for (int i = 0; i < 3; i++)
            mavlink_msg_waypoint_ack_send(_channel, msg->sysid,
                                          msg->compid, type);

        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT_SET_CURRENT: {
        sendText(SEVERITY_LOW, PSTR("waypoint set current"));

        // decode
        mavlink_waypoint_set_current_t packet;
        mavlink_msg_waypoint_set_current_decode(msg, &packet);
        Serial.print("Packet Sequence:");
        Serial.println(packet.seq);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        // set current waypoint
        Serial.print("Current Index:");
        Serial.println(_guide->getCurrentIndex());
        Serial.flush();
        _guide->setCurrentIndex(packet.seq);
        mavlink_msg_waypoint_current_send(_channel,
                                          _guide->getCurrentIndex());
        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT_COUNT: {
        sendText(SEVERITY_LOW, PSTR("waypoint count"));

        // decode
        mavlink_waypoint_count_t packet;
        mavlink_msg_waypoint_count_decode(msg, &packet);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        // start waypoint receiving
        if (packet.count > _cmdMax) {
            packet.count = _cmdMax;
        }
        _cmdNumberRequested = packet.count;
        _cmdTimeLastReceived = millis();
        _receivingCmds = true;
        _sendingCmds = false;
        _cmdRequestIndex = 0;
        break;
    }

    case MAVLINK_MSG_ID_WAYPOINT: {
        sendText(SEVERITY_LOW, PSTR("waypoint"));

        // Check if receiving waypiont
        if (!_receivingCmds) {
            //sendText(SEVERITY_HIGH, PSTR("not receiving commands"));
            break;
        }

        // decode
        mavlink_waypoint_t packet;
        mavlink_msg_waypoint_decode(msg, &packet);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        // check if this is the requested waypoint
        if (packet.seq != _cmdRequestIndex) {
            char warningMsg[50];
            sprintf(warningMsg,
                    "waypoint request out of sequence: (packet) %d / %d (ap)",
                    packet.seq, _cmdRequestIndex);
            sendText(SEVERITY_HIGH, warningMsg);
            break;
        }

        _hal->debug->printf_P(PSTR("received waypoint x: %f\ty: %f\tz: %f\n"),
                              packet.x,
                              packet.y,
                              packet.z);

        // store waypoint
        AP_MavlinkCommand command(packet);
        //sendText(SEVERITY_HIGH, PSTR("waypoint stored"));
        _cmdRequestIndex++;
        if (_cmdRequestIndex == _cmdNumberRequested) {
            sendMessage(MAVLINK_MSG_ID_WAYPOINT_ACK);
            _receivingCmds = false;
            _guide->setNumberOfCommands(_cmdNumberRequested);
            //sendText(SEVERITY_LOW, PSTR("waypoint ack sent"));
        } else if (_cmdRequestIndex > _cmdNumberRequested) {
            _receivingCmds = false;
        }
        _cmdTimeLastReceived = millis();
        break;
    }

    case MAVLINK_MSG_ID_PARAM_SET: {
        sendText(SEVERITY_LOW, PSTR("param set"));
        AP_Var *vp;
        AP_Meta_class::Type_id var_type;

        // decode
        mavlink_param_set_t packet;
        mavlink_msg_param_set_decode(msg, &packet);
        if (_checkTarget(packet.target_system, packet.target_component))
            break;

        // set parameter

        char key[_paramNameLengthMax + 1];
        strncpy(key, (char *) packet.param_id, _paramNameLengthMax);
        key[_paramNameLengthMax] = 0;

        // find the requested parameter
        vp = AP_Var::find(key);
        if ((NULL != vp) && // exists
                !isnan(packet.param_value) && // not nan
                !isinf(packet.param_value)) { // not inf

            // add a small amount before casting parameter values
            // from float to integer to avoid truncating to the
            // next lower integer value.
            const float rounding_addition = 0.01;

            // fetch the variable type ID
            var_type = vp->meta_type_id();

            // handle variables with standard type IDs
            if (var_type == AP_Var::k_typeid_float) {
                ((AP_Float *) vp)->set_and_save(packet.param_value);

            } else if (var_type == AP_Var::k_typeid_float16) {
                ((AP_Float16 *) vp)->set_and_save(packet.param_value);

            } else if (var_type == AP_Var::k_typeid_int32) {
                ((AP_Int32 *) vp)->set_and_save(
                    packet.param_value + rounding_addition);

            } else if (var_type == AP_Var::k_typeid_int16) {
                ((AP_Int16 *) vp)->set_and_save(
                    packet.param_value + rounding_addition);

            } else if (var_type == AP_Var::k_typeid_int8) {
                ((AP_Int8 *) vp)->set_and_save(
                    packet.param_value + rounding_addition);
            } else {
                // we don't support mavlink set on this parameter
                break;
            }

            // Report back the new value if we accepted the change
            // we send the value we actually set, which could be
            // different from the value sent, in case someone sent
            // a fractional value to an integer type
            mavlink_msg_param_value_send(_channel, (int8_t *) key,
                                         vp->cast_to_float(), _countParameters(), -1); // XXX we don't actually know what its index is...
        }

        break;
    } // end case


    }
}

uint16_t MavlinkComm::_countParameters() {
    // if we haven't cached the parameter count yet...
    if (0 == _parameterCount) {
        AP_Var *vp;

        vp = AP_Var::first();
        do {
            // if a parameter responds to cast_to_float then we are going to be able to report it
            if (!isnan(vp->cast_to_float())) {
                _parameterCount++;
            }
        } while (NULL != (vp = vp->next()));
    }
    return _parameterCount;
}

AP_Var * _findParameter(uint16_t index) {
    AP_Var *vp;

    vp = AP_Var::first();
    while (NULL != vp) {

        // if the parameter is reportable
        if (!(isnan(vp->cast_to_float()))) {
            // if we have counted down to the index we want
            if (0 == index) {
                // return the parameter
                return vp;
            }
            // count off this parameter, as it is reportable but not
            // the one we want
            index--;
        }
        // and move to the next parameter
        vp = vp->next();
    }
    return NULL;
}

// check the target
uint8_t MavlinkComm::_checkTarget(uint8_t sysid, uint8_t compid) {
    /*
     char msg[50];
     sprintf(msg, "target = %d / %d\tcomp = %d / %d", sysid,
     mavlink_system.sysid, compid, mavlink_system.compid);
     sendText(SEVERITY_LOW, msg);
     */
    if (sysid != mavlink_system.sysid) {
        //sendText(SEVERITY_LOW, PSTR("system id mismatch"));
        return 1;

    } else if (compid != mavlink_system.compid) {
        //sendText(SEVERITY_LOW, PSTR("component id mismatch"));
        return 0; // XXX currently not receiving correct compid from gcs

    } else {
        return 0; // no error
    }
}

} // apo
// vim:ts=4:sw=4:expandtab