GCS_Common.cpp

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/*
  Common GCS MAVLink functions for all vehicle types

   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, see <http://www.gnu.org/licenses/>.
 */
#include <AP_AHRS/AP_AHRS.h>
#include <AP_HAL/AP_HAL.h>
#include <AP_OpticalFlow/AP_OpticalFlow.h>
#include <AP_Vehicle/AP_Vehicle.h>
#include <AP_RangeFinder/RangeFinder_Backend.h>
#include <AP_Airspeed/AP_Airspeed.h>

#include "GCS.h"

#include <stdio.h>
#if CONFIG_HAL_BOARD == HAL_BOARD_PX4 || CONFIG_HAL_BOARD == HAL_BOARD_VRBRAIN
#include <drivers/drv_pwm_output.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#endif

#if HAL_RCINPUT_WITH_AP_RADIO
#include <AP_Radio/AP_Radio.h>
#include <AP_BoardConfig/AP_BoardConfig.h>
#endif

#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
#include <SITL/SITL.h>
#endif

extern const AP_HAL::HAL& hal;

uint32_t GCS_MAVLINK::last_radio_status_remrssi_ms;
uint8_t GCS_MAVLINK::mavlink_active = 0;
uint8_t GCS_MAVLINK::chan_is_streaming = 0;
uint32_t GCS_MAVLINK::reserve_param_space_start_ms;

GCS *GCS::_singleton = nullptr;

GCS_MAVLINK::GCS_MAVLINK()
{
    AP_Param::setup_object_defaults(this, var_info);
}

void
GCS_MAVLINK::init(AP_HAL::UARTDriver *port, mavlink_channel_t mav_chan)
{
    if (!valid_channel(mav_chan)) {
        return;
    }

    _port = port;
    chan = mav_chan;

    mavlink_comm_port[chan] = _port;
    _queued_parameter = nullptr;

    snprintf(_perf_packet_name, sizeof(_perf_packet_name), "GCS_Packet_%u", chan);
    _perf_packet = hal.util->perf_alloc(AP_HAL::Util::PC_ELAPSED, _perf_packet_name);

    snprintf(_perf_update_name, sizeof(_perf_update_name), "GCS_Update_%u", chan);
    _perf_update = hal.util->perf_alloc(AP_HAL::Util::PC_ELAPSED, _perf_update_name);

    initialised = true;
}


/*
  setup a UART, handling begin() and init()
 */
void
GCS_MAVLINK::setup_uart(const AP_SerialManager& serial_manager, AP_SerialManager::SerialProtocol protocol, uint8_t instance)
{
    serialmanager_p = &serial_manager;

    // search for serial port
    
    AP_HAL::UARTDriver *uart;
    uart = serial_manager.find_serial(protocol, instance);
    if (uart == nullptr) {
        // return immediately if not found
        return;
    }

    // get associated mavlink channel
    mavlink_channel_t mav_chan;
    if (!serial_manager.get_mavlink_channel(protocol, instance, mav_chan)) {
        // return immediately in unlikely case mavlink channel cannot be found
        return;
    }

    /*
      Now try to cope with SiK radios that may be stuck in bootloader
      mode because CTS was held while powering on. This tells the
      bootloader to wait for a firmware. It affects any SiK radio with
      CTS connected that is externally powered. To cope we send 0x30
      0x20 at 115200 on startup, which tells the bootloader to reset
      and boot normally
     */
    uart->begin(115200);
    AP_HAL::UARTDriver::flow_control old_flow_control = uart->get_flow_control();
    uart->set_flow_control(AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE);
    for (uint8_t i=0; i<3; i++) {
        hal.scheduler->delay(1);
        uart->write(0x30);
        uart->write(0x20);
    }
    // since tcdrain() and TCSADRAIN may not be implemented...
    hal.scheduler->delay(1);
    
    uart->set_flow_control(old_flow_control);

    // now change back to desired baudrate
    uart->begin(serial_manager.find_baudrate(protocol, instance));

    // and init the gcs instance
    init(uart, mav_chan);

    AP_SerialManager::SerialProtocol mavlink_protocol = serialmanager_p->get_mavlink_protocol(mav_chan);
    mavlink_status_t *status = mavlink_get_channel_status(chan);
    if (status == nullptr) {
        return;
    }
    
    if (mavlink_protocol == AP_SerialManager::SerialProtocol_MAVLink2) {
        // load signing key
        load_signing_key();

        if (status->signing == nullptr) {
            // if signing is off start by sending MAVLink1.
            status->flags |= MAVLINK_STATUS_FLAG_OUT_MAVLINK1;
        }
        // announce that we are MAVLink2 capable
        hal.util->set_capabilities(MAV_PROTOCOL_CAPABILITY_MAVLINK2);
    } else if (status) {
        // user has asked to only send MAVLink1
        status->flags |= MAVLINK_STATUS_FLAG_OUT_MAVLINK1;
    }

    if (chan == MAVLINK_COMM_0) {
        // Always start with MAVLink1 on first port for now, to allow for recovery
        // after experiments with MAVLink2
        status->flags |= MAVLINK_STATUS_FLAG_OUT_MAVLINK1;
    }
}


void
GCS_MAVLINK::queued_waypoint_send()
{
    if (initialised &&
        waypoint_receiving &&
        waypoint_request_i <= waypoint_request_last) {
        mavlink_msg_mission_request_send(
            chan,
            waypoint_dest_sysid,
            waypoint_dest_compid,
            waypoint_request_i,
            MAV_MISSION_TYPE_MISSION);
    }
}

void GCS_MAVLINK::send_meminfo(void)
{
    unsigned __brkval = 0;
    uint32_t memory = hal.util->available_memory();
    mavlink_msg_meminfo_send(chan, __brkval, MIN(memory, 0xFFFFU), memory);
}

// report power supply status
void GCS_MAVLINK::send_power_status(void)
{
    mavlink_msg_power_status_send(chan,
                                  hal.analogin->board_voltage() * 1000,
                                  hal.analogin->servorail_voltage() * 1000,
                                  hal.analogin->power_status_flags());
}

void GCS_MAVLINK::send_battery_status(const AP_BattMonitor &battery,
                                      const uint8_t instance) const
{
    // catch the battery backend not supporting the required number of cells
    static_assert(sizeof(AP_BattMonitor::cells) >= (sizeof(uint16_t) * MAVLINK_MSG_BATTERY_STATUS_FIELD_VOLTAGES_LEN),
                  "Not enough battery cells for the MAVLink message");

    float temp;
    bool got_temperature = battery.get_temperature(temp, instance);
    mavlink_msg_battery_status_send(chan,
                                    instance, // id
                                    MAV_BATTERY_FUNCTION_UNKNOWN, // function
                                    MAV_BATTERY_TYPE_UNKNOWN, // type
                                    got_temperature ? ((int16_t) (temp * 100)) : INT16_MAX, // temperature. INT16_MAX if unknown
                                    battery.get_cell_voltages(instance).cells, // cell voltages
                                    battery.has_current(instance) ? battery.current_amps(instance) * 100 : -1, // current in centiampere
                                    battery.has_current(instance) ? battery.consumed_mah(instance) : -1,       // total consumed current in milliampere.hour
                                    battery.has_consumed_energy(instance) ? battery.consumed_wh(instance) * 36 : -1, // consumed energy in hJ (hecto-Joules)
                                    battery.capacity_remaining_pct(instance));
}

// returns true if all battery instances were reported
bool GCS_MAVLINK::send_battery_status() const
{
    const AP_BattMonitor &battery = AP::battery();

    for(uint8_t i = 0; i < battery.num_instances(); i++) {
        CHECK_PAYLOAD_SIZE(BATTERY_STATUS);
        send_battery_status(battery, i);
    }
    return true;
}

void GCS_MAVLINK::send_distance_sensor(const AP_RangeFinder_Backend *sensor, const uint8_t instance) const
{
    if (!sensor->has_data()) {
        return;
    }

    mavlink_msg_distance_sensor_send(
        chan,
        AP_HAL::millis(),                        // time since system boot TODO: take time of measurement
        sensor->min_distance_cm(),               // minimum distance the sensor can measure in centimeters
        sensor->max_distance_cm(),               // maximum distance the sensor can measure in centimeters
        sensor->distance_cm(),                   // current distance reading
        sensor->get_mav_distance_sensor_type(),  // type from MAV_DISTANCE_SENSOR enum
        instance,                                // onboard ID of the sensor == instance
        sensor->orientation(),                   // direction the sensor faces from MAV_SENSOR_ORIENTATION enum
        0);                                      // Measurement covariance in centimeters, 0 for unknown / invalid readings
}

bool GCS_MAVLINK::send_distance_sensor() const
{
    RangeFinder *rangefinder = RangeFinder::get_singleton();
    if (rangefinder == nullptr) {
        return true; // this is wrong, but pretend we sent data and don't requeue
    }

    // if we have a proximity backend that utilizes rangefinders cull sending them here,
    // and allow the later proximity code to manage them
    bool filter_possible_proximity_sensors = false;
    AP_Proximity *proximity = AP_Proximity::get_singleton();
    if (proximity != nullptr) {
        for (uint8_t i = 0; i < proximity->num_sensors(); i++) {
            if (proximity->get_type(i) == AP_Proximity::Proximity_Type_RangeFinder) {
                filter_possible_proximity_sensors = true;
            }
        }
    }

    for (uint8_t i = 0; i < RANGEFINDER_MAX_INSTANCES; i++) {
        CHECK_PAYLOAD_SIZE(DISTANCE_SENSOR);
        AP_RangeFinder_Backend *sensor = rangefinder->get_backend(i);
        if (sensor == nullptr) {
            continue;
        }
        enum Rotation orient = sensor->orientation();
        if (!filter_possible_proximity_sensors ||
            (orient > ROTATION_YAW_315 && orient != ROTATION_PITCH_90)) {
            send_distance_sensor(sensor, i);
        }
    }
    return true;
}

void GCS_MAVLINK::send_rangefinder_downward() const
{
    RangeFinder *rangefinder = RangeFinder::get_singleton();
    if (rangefinder == nullptr) {
        return;
    }
    AP_RangeFinder_Backend *s = rangefinder->find_instance(ROTATION_PITCH_270);
    if (s == nullptr) {
        return;
    }
    mavlink_msg_rangefinder_send(
            chan,
            s->distance_cm() * 0.01f,
            s->voltage_mv() * 0.001f);
}

bool GCS_MAVLINK::send_proximity() const
{
    AP_Proximity *proximity = AP_Proximity::get_singleton();
    if (proximity == nullptr || proximity->get_status() == AP_Proximity::Proximity_NotConnected) {
        return true; // this is wrong, but pretend we sent data and don't requeue
    }

    const uint16_t dist_min = (uint16_t)(proximity->distance_min() * 100.0f); // minimum distance the sensor can measure in centimeters
    const uint16_t dist_max = (uint16_t)(proximity->distance_max() * 100.0f); // maximum distance the sensor can measure in centimeters
    // send horizontal distances
    AP_Proximity::Proximity_Distance_Array dist_array;
    if (proximity->get_horizontal_distances(dist_array)) {
        for (uint8_t i = 0; i < PROXIMITY_MAX_DIRECTION; i++) {
            CHECK_PAYLOAD_SIZE(DISTANCE_SENSOR);
            mavlink_msg_distance_sensor_send(
                    chan,
                    AP_HAL::millis(),                               // time since system boot
                    dist_min,                                       // minimum distance the sensor can measure in centimeters
                    dist_max,                                       // maximum distance the sensor can measure in centimeters
                    (uint16_t)(dist_array.distance[i] * 100.0f),    // current distance reading
                    MAV_DISTANCE_SENSOR_LASER,                      // type from MAV_DISTANCE_SENSOR enum
                    PROXIMITY_SENSOR_ID_START + i,                  // onboard ID of the sensor
                    dist_array.orientation[i],                      // direction the sensor faces from MAV_SENSOR_ORIENTATION enum
                    0);                                             // Measurement covariance in centimeters, 0 for unknown / invalid readings
        }
    }

    // send upward distance
    float dist_up;
    if (proximity->get_upward_distance(dist_up)) {
        CHECK_PAYLOAD_SIZE(DISTANCE_SENSOR);
        mavlink_msg_distance_sensor_send(
                chan,
                AP_HAL::millis(),                                         // time since system boot
                dist_min,                                                 // minimum distance the sensor can measure in centimeters
                dist_max,                                                 // maximum distance the sensor can measure in centimeters
                (uint16_t)(dist_up * 100.0f),                             // current distance reading
                MAV_DISTANCE_SENSOR_LASER,                                // type from MAV_DISTANCE_SENSOR enum
                PROXIMITY_SENSOR_ID_START + PROXIMITY_MAX_DIRECTION + 1,  // onboard ID of the sensor
                MAV_SENSOR_ROTATION_PITCH_90,                             // direction upwards
                0);                                                       // Measurement covariance in centimeters, 0 for unknown / invalid readings
    }
    return true;
}

// report AHRS2 state
void GCS_MAVLINK::send_ahrs2()
{
#if AP_AHRS_NAVEKF_AVAILABLE
    const AP_AHRS &ahrs = AP::ahrs();
    Vector3f euler;
    struct Location loc {};
    if (ahrs.get_secondary_attitude(euler)) {
        mavlink_msg_ahrs2_send(chan,
                               euler.x,
                               euler.y,
                               euler.z,
                               loc.alt*1.0e-2f,
                               loc.lat,
                               loc.lng);
    }
    const AP_AHRS_NavEKF &_ahrs = reinterpret_cast<const AP_AHRS_NavEKF&>(ahrs);
    const NavEKF2 &ekf2 = _ahrs.get_NavEKF2_const();
    if (ekf2.activeCores() > 0 &&
        HAVE_PAYLOAD_SPACE(chan, AHRS3)) {
        ekf2.getLLH(loc);
        ekf2.getEulerAngles(-1,euler);
        mavlink_msg_ahrs3_send(chan,
                               euler.x,
                               euler.y,
                               euler.z,
                               loc.alt*1.0e-2f,
                               loc.lat,
                               loc.lng,
                               0, 0, 0, 0);
    }
#endif
}

/*
  handle a MISSION_REQUEST_LIST mavlink packet
 */
void GCS_MAVLINK::handle_mission_request_list(AP_Mission &mission, mavlink_message_t *msg)
{
    // decode
    mavlink_mission_request_list_t packet;
    mavlink_msg_mission_request_list_decode(msg, &packet);

    // reply with number of commands in the mission.  The GCS will then request each command separately
    mavlink_msg_mission_count_send(chan,msg->sysid, msg->compid, mission.num_commands(),
                                   MAV_MISSION_TYPE_MISSION);

    // set variables to help handle the expected sending of commands to the GCS
    waypoint_receiving = false;             // record that we are sending commands (i.e. not receiving)
}

/*
  handle a MISSION_REQUEST mavlink packet
 */
void GCS_MAVLINK::handle_mission_request(AP_Mission &mission, mavlink_message_t *msg)
{
    AP_Mission::Mission_Command cmd;

    if (msg->msgid == MAVLINK_MSG_ID_MISSION_REQUEST_INT) {  
        // decode
        mavlink_mission_request_int_t packet;
        mavlink_msg_mission_request_int_decode(msg, &packet);

        // retrieve mission from eeprom
        if (!mission.read_cmd_from_storage(packet.seq, cmd)) {
            goto mission_item_send_failed;
        }

        mavlink_mission_item_int_t ret_packet;
        memset(&ret_packet, 0, sizeof(ret_packet));
        if (!AP_Mission::mission_cmd_to_mavlink_int(cmd, ret_packet)) {
            goto mission_item_send_failed;
        }

        // set packet's current field to 1 if this is the command being executed
        if (cmd.id == (uint16_t)mission.get_current_nav_cmd().index) {
            ret_packet.current = 1;
        } else {
            ret_packet.current = 0;
        }

        // set auto continue to 1
        ret_packet.autocontinue = 1;     // 1 (true), 0 (false)

        /*
          avoid the _send() function to save memory, as it avoids
          the stack usage of the _send() function by using the already
          declared ret_packet above
         */
        ret_packet.target_system = msg->sysid;
        ret_packet.target_component = msg->compid;
        ret_packet.seq = packet.seq;
        ret_packet.command = cmd.id;

        _mav_finalize_message_chan_send(chan, 
                                        MAVLINK_MSG_ID_MISSION_ITEM_INT,
                                        (const char *)&ret_packet,
                                        MAVLINK_MSG_ID_MISSION_ITEM_MIN_LEN,
                                        MAVLINK_MSG_ID_MISSION_ITEM_INT_LEN,
                                        MAVLINK_MSG_ID_MISSION_ITEM_INT_CRC);
    } else {
        // decode
        mavlink_mission_request_t packet;
        mavlink_msg_mission_request_decode(msg, &packet);

        if (packet.seq != 0 && // always allow HOME to be read
            packet.seq >= mission.num_commands()) {
            // try to educate the GCS on the actual size of the mission:
            mavlink_msg_mission_count_send(chan,msg->sysid, msg->compid, mission.num_commands(),
                                           MAV_MISSION_TYPE_MISSION);
            goto mission_item_send_failed;
        }

        // retrieve mission from eeprom
        if (!mission.read_cmd_from_storage(packet.seq, cmd)) {
            goto mission_item_send_failed;
        }

        mavlink_mission_item_t ret_packet;
        memset(&ret_packet, 0, sizeof(ret_packet));
        if (!AP_Mission::mission_cmd_to_mavlink(cmd, ret_packet)) {
            goto mission_item_send_failed;
        }
            
        // set packet's current field to 1 if this is the command being executed
        if (cmd.id == (uint16_t)mission.get_current_nav_cmd().index) {
            ret_packet.current = 1;
        } else {
            ret_packet.current = 0;
        }

        // set auto continue to 1
        ret_packet.autocontinue = 1;     // 1 (true), 0 (false)

        /*
          avoid the _send() function to save memory, as it avoids
          the stack usage of the _send() function by using the already
          declared ret_packet above
         */
        ret_packet.target_system = msg->sysid;
        ret_packet.target_component = msg->compid;
        ret_packet.seq = packet.seq;
        ret_packet.command = cmd.id;

        _mav_finalize_message_chan_send(chan, 
                                        MAVLINK_MSG_ID_MISSION_ITEM,
                                        (const char *)&ret_packet,
                                        MAVLINK_MSG_ID_MISSION_ITEM_MIN_LEN,
                                        MAVLINK_MSG_ID_MISSION_ITEM_LEN,
                                        MAVLINK_MSG_ID_MISSION_ITEM_CRC);
    }

    return;

mission_item_send_failed:
    // send failure message
    mavlink_msg_mission_ack_send(chan, msg->sysid, msg->compid, MAV_MISSION_ERROR,
                                 MAV_MISSION_TYPE_MISSION);
}

/*
  handle a MISSION_SET_CURRENT mavlink packet
 */
void GCS_MAVLINK::handle_mission_set_current(AP_Mission &mission, mavlink_message_t *msg)
{
    // decode
    mavlink_mission_set_current_t packet;
    mavlink_msg_mission_set_current_decode(msg, &packet);

    // set current command
    if (mission.set_current_cmd(packet.seq)) {
        mavlink_msg_mission_current_send(chan, packet.seq);
    }
}

/*
  handle a MISSION_COUNT mavlink packet
 */
void GCS_MAVLINK::handle_mission_count(AP_Mission &mission, mavlink_message_t *msg)
{
    // decode
    mavlink_mission_count_t packet;
    mavlink_msg_mission_count_decode(msg, &packet);

    // start waypoint receiving
    if (packet.count > mission.num_commands_max()) {
        // send NAK
        mavlink_msg_mission_ack_send(chan, msg->sysid, msg->compid, MAV_MISSION_NO_SPACE,
                                     MAV_MISSION_TYPE_MISSION);
        return;
    }

    // new mission arriving, truncate mission to be the same length
    mission.truncate(packet.count);

    // set variables to help handle the expected receiving of commands from the GCS
    waypoint_timelast_receive = AP_HAL::millis();    // set time we last received commands to now
    waypoint_receiving = true;              // record that we expect to receive commands
    waypoint_request_i = 0;                 // reset the next expected command number to zero
    waypoint_request_last = packet.count;   // record how many commands we expect to receive
    waypoint_timelast_request = 0;          // set time we last requested commands to zero

    waypoint_dest_sysid = msg->sysid;       // record system id of GCS who wants to upload the mission
    waypoint_dest_compid = msg->compid;     // record component id of GCS who wants to upload the mission
}

/*
  handle a MISSION_CLEAR_ALL mavlink packet
 */
void GCS_MAVLINK::handle_mission_clear_all(AP_Mission &mission, mavlink_message_t *msg)
{
    // decode
    mavlink_mission_clear_all_t packet;
    mavlink_msg_mission_clear_all_decode(msg, &packet);

    // clear all waypoints
    if (mission.clear()) {
        // send ack
        mavlink_msg_mission_ack_send(chan, msg->sysid, msg->compid, MAV_MISSION_ACCEPTED,
                                     MAV_MISSION_TYPE_MISSION);
    }else{
        // send nack
        mavlink_msg_mission_ack_send(chan, msg->sysid, msg->compid, MAV_MISSION_ERROR,
                                     MAV_MISSION_TYPE_MISSION);
    }
}

/*
  handle a MISSION_WRITE_PARTIAL_LIST mavlink packet
 */
void GCS_MAVLINK::handle_mission_write_partial_list(AP_Mission &mission, mavlink_message_t *msg)
{
    // decode
    mavlink_mission_write_partial_list_t packet;
    mavlink_msg_mission_write_partial_list_decode(msg, &packet);

    // start waypoint receiving
    if ((unsigned)packet.start_index > mission.num_commands() ||
        (unsigned)packet.end_index > mission.num_commands() ||
        packet.end_index < packet.start_index) {
        send_text(MAV_SEVERITY_WARNING,"Flight plan update rejected");
        return;
    }

    waypoint_timelast_receive = AP_HAL::millis();
    waypoint_timelast_request = 0;
    waypoint_receiving   = true;
    waypoint_request_i   = packet.start_index;
    waypoint_request_last= packet.end_index;

    waypoint_dest_sysid = msg->sysid;       // record system id of GCS who wants to partially update the mission
    waypoint_dest_compid = msg->compid;     // record component id of GCS who wants to partially update the mission
}


/*
  handle a GIMBAL_REPORT mavlink packet
 */
void GCS_MAVLINK::handle_gimbal_report(AP_Mount &mount, mavlink_message_t *msg) const
{
    mount.handle_gimbal_report(chan, msg);
}


void GCS_MAVLINK::send_text(MAV_SEVERITY severity, const char *fmt, ...)
{
    char text[MAVLINK_MSG_STATUSTEXT_FIELD_TEXT_LEN+1] {};
    va_list arg_list;
    va_start(arg_list, fmt);
    hal.util->vsnprintf((char *)text, sizeof(text), fmt, arg_list);
    va_end(arg_list);
    text[MAVLINK_MSG_STATUSTEXT_FIELD_TEXT_LEN] = 0;
    gcs().send_statustext(severity, (1<<chan), text);
}

void GCS_MAVLINK::handle_radio_status(mavlink_message_t *msg, DataFlash_Class &dataflash, bool log_radio)
{
    mavlink_radio_t packet;
    mavlink_msg_radio_decode(msg, &packet);

    // record if the GCS has been receiving radio messages from
    // the aircraft
    if (packet.remrssi != 0) {
        last_radio_status_remrssi_ms = AP_HAL::millis();
    }

    // use the state of the transmit buffer in the radio to
    // control the stream rate, giving us adaptive software
    // flow control
    if (packet.txbuf < 20 && stream_slowdown < 100) {
        // we are very low on space - slow down a lot
        stream_slowdown += 3;
    } else if (packet.txbuf < 50 && stream_slowdown < 100) {
        // we are a bit low on space, slow down slightly
        stream_slowdown += 1;
    } else if (packet.txbuf > 95 && stream_slowdown > 10) {
        // the buffer has plenty of space, speed up a lot
        stream_slowdown -= 2;
    } else if (packet.txbuf > 90 && stream_slowdown != 0) {
        // the buffer has enough space, speed up a bit
        stream_slowdown--;
    }

    //log rssi, noise, etc if logging Performance monitoring data
    if (log_radio) {
        dataflash.Log_Write_Radio(packet);
    }
}

/*
  handle an incoming mission item
  return true if this is the last mission item, otherwise false
 */
bool GCS_MAVLINK::handle_mission_item(mavlink_message_t *msg, AP_Mission &mission)
{
    MAV_MISSION_RESULT result = MAV_MISSION_ACCEPTED;
    struct AP_Mission::Mission_Command cmd = {};
    bool mission_is_complete = false;
    uint16_t seq=0;
    uint16_t current = 0;
    
    if (msg->msgid == MAVLINK_MSG_ID_MISSION_ITEM) {      
        mavlink_mission_item_t packet;    
        mavlink_msg_mission_item_decode(msg, &packet);
        
        // convert mavlink packet to mission command
        result = AP_Mission::mavlink_to_mission_cmd(packet, cmd);
        if (result != MAV_MISSION_ACCEPTED) {
            goto mission_ack;
        }
        
        seq = packet.seq;
        current = packet.current;
    } else {
        mavlink_mission_item_int_t packet;
        mavlink_msg_mission_item_int_decode(msg, &packet);
        
        // convert mavlink packet to mission command
        result = AP_Mission::mavlink_int_to_mission_cmd(packet, cmd);
        if (result != MAV_MISSION_ACCEPTED) {
            goto mission_ack;
        }
        
        seq = packet.seq;
        current = packet.current;
    }

    if (current == 2) {                                               
        // current = 2 is a flag to tell us this is a "guided mode"
        // waypoint and not for the mission
        result = (handle_guided_request(cmd) ? MAV_MISSION_ACCEPTED
                                             : MAV_MISSION_ERROR) ;

        // verify we received the command
        goto mission_ack;
    }

    if (current == 3) {
        //current = 3 is a flag to tell us this is a alt change only
        // add home alt if needed
        handle_change_alt_request(cmd);

        // verify we recevied the command
        result = MAV_MISSION_ACCEPTED;
        goto mission_ack;
    }

    // Check if receiving waypoints (mission upload expected)
    if (!waypoint_receiving) {
        result = MAV_MISSION_ERROR;
        goto mission_ack;
    }

    // check if this is the requested waypoint
    if (seq != waypoint_request_i) {
        result = MAV_MISSION_INVALID_SEQUENCE;
        goto mission_ack;
    }

    // sanity check for DO_JUMP command
    if (cmd.id == MAV_CMD_DO_JUMP) {
        if ((cmd.content.jump.target >= mission.num_commands() && cmd.content.jump.target >= waypoint_request_last) || cmd.content.jump.target == 0) {
            result = MAV_MISSION_ERROR;
            goto mission_ack;
        }
    }
    
    // if command index is within the existing list, replace the command
    if (seq < mission.num_commands()) {
        if (mission.replace_cmd(seq,cmd)) {
            result = MAV_MISSION_ACCEPTED;
        }else{
            result = MAV_MISSION_ERROR;
            goto mission_ack;
        }
        // if command is at the end of command list, add the command
    } else if (seq == mission.num_commands()) {
        if (mission.add_cmd(cmd)) {
            result = MAV_MISSION_ACCEPTED;
        }else{
            result = MAV_MISSION_ERROR;
            goto mission_ack;
        }
        // if beyond the end of the command list, return an error
    } else {
        result = MAV_MISSION_ERROR;
        goto mission_ack;
    }
    
    // update waypoint receiving state machine
    waypoint_timelast_receive = AP_HAL::millis();
    waypoint_request_i++;
    
    if (waypoint_request_i >= waypoint_request_last) {
        mavlink_msg_mission_ack_send_buf(
            msg,
            chan,
            msg->sysid,
            msg->compid,
            MAV_MISSION_ACCEPTED,
            MAV_MISSION_TYPE_MISSION);
        
        send_text(MAV_SEVERITY_INFO,"Flight plan received");
        waypoint_receiving = false;
        mission_is_complete = true;
        // XXX ignores waypoint radius for individual waypoints, can
        // only set WP_RADIUS parameter
    } else {
        waypoint_timelast_request = AP_HAL::millis();
        // if we have enough space, then send the next WP immediately
        if (HAVE_PAYLOAD_SPACE(chan, MISSION_ITEM)) {
            queued_waypoint_send();
        } else {
            send_message(MSG_NEXT_WAYPOINT);
        }
    }
    return mission_is_complete;

mission_ack:
    // we are rejecting the mission/waypoint
    mavlink_msg_mission_ack_send_buf(
        msg,
        chan,
        msg->sysid,
        msg->compid,
        result,
        MAV_MISSION_TYPE_MISSION);

    return mission_is_complete;
}

void GCS_MAVLINK::push_deferred_messages()
{
    while (num_deferred_messages != 0) {
        if (!try_send_message(deferred_messages[next_deferred_message])) {
            break;
        }
        next_deferred_message++;
        if (next_deferred_message == ARRAY_SIZE(deferred_messages)) {
            next_deferred_message = 0;
        }
        num_deferred_messages--;
    }
}

void GCS_MAVLINK::retry_deferred()
{
    push_deferred_messages();
}

// send a message using mavlink, handling message queueing
void GCS_MAVLINK::send_message(enum ap_message id)
{
    uint8_t i, nextid;

    if (id == MSG_HEARTBEAT) {
        save_signing_timestamp(false);
    }

    // see if we can send the deferred messages, if any:
    push_deferred_messages();

    // if there are no deferred messages, attempt to send straight away:
    if (num_deferred_messages == 0) {
        if (try_send_message(id)) {
            // yay, we sent it!
            return;
        }
    }

    // we failed to send the message this time around, so try to defer:
    if (num_deferred_messages == ARRAY_SIZE(deferred_messages)) {
        // the defer buffer is full, discard this attempt to send.
        // Note that the message *may* already be in the defer buffer
        return;
    }

    // check if this message is deferred:
    for (i=0, nextid = next_deferred_message; i < num_deferred_messages; i++) {
        if (deferred_messages[nextid] == id) {
            // it's already deferred
            return;
        }
        nextid++;
        if (nextid == ARRAY_SIZE(deferred_messages)) {
            nextid = 0;
        }
    }

    // not already deferred, defer it
    deferred_messages[nextid] = id;
    num_deferred_messages++;
}

void GCS_MAVLINK::packetReceived(const mavlink_status_t &status,
                                 mavlink_message_t &msg)
{
    // we exclude radio packets because we historically used this to
    // make it possible to use the CLI over the radio
    if (msg.msgid != MAVLINK_MSG_ID_RADIO && msg.msgid != MAVLINK_MSG_ID_RADIO_STATUS) {
        mavlink_active |= (1U<<(chan-MAVLINK_COMM_0));
    }
    if (!(status.flags & MAVLINK_STATUS_FLAG_IN_MAVLINK1) &&
        (status.flags & MAVLINK_STATUS_FLAG_OUT_MAVLINK1) &&
        serialmanager_p &&
        serialmanager_p->get_mavlink_protocol(chan) == AP_SerialManager::SerialProtocol_MAVLink2) {
        // if we receive any MAVLink2 packets on a connection
        // currently sending MAVLink1 then switch to sending
        // MAVLink2
        mavlink_status_t *cstatus = mavlink_get_channel_status(chan);
        if (cstatus != nullptr) {
            cstatus->flags &= ~MAVLINK_STATUS_FLAG_OUT_MAVLINK1;
        }
    }
    if (routing.check_and_forward(chan, &msg) &&
        accept_packet(status, msg)) {
        handleMessage(&msg);
    }
}

void
GCS_MAVLINK::update(uint32_t max_time_us)
{
    // receive new packets
    mavlink_message_t msg;
    mavlink_status_t status;
    uint32_t tstart_us = AP_HAL::micros();
    uint32_t now_ms = AP_HAL::millis();

    hal.util->perf_begin(_perf_update);

    status.packet_rx_drop_count = 0;

    // process received bytes
    uint16_t nbytes = comm_get_available(chan);
    for (uint16_t i=0; i<nbytes; i++)
    {
        const uint8_t c = (uint8_t)_port->read();
        const uint32_t protocol_timeout = 4000;
        
        if (alternative.handler &&
            now_ms - alternative.last_mavlink_ms > protocol_timeout) {
            /*
              we have an alternative protocol handler installed and we
              haven't parsed a MAVLink packet for 4 seconds. Try
              parsing using alternative handler
             */
            if (alternative.handler(c, mavlink_comm_port[chan])) {
                alternative.last_alternate_ms = now_ms;
                gcs_alternative_active[chan] = true;
            }
            
            /*
              we may also try parsing as MAVLink if we haven't had a
              successful parse on the alternative protocol for 4s
             */
            if (now_ms - alternative.last_alternate_ms <= protocol_timeout) {
                continue;
            }
        }

        bool parsed_packet = false;

        // Try to get a new message
        if (mavlink_parse_char(chan, c, &msg, &status)) {
            hal.util->perf_begin(_perf_packet);
            packetReceived(status, msg);
            hal.util->perf_end(_perf_packet);
            parsed_packet = true;
            gcs_alternative_active[chan] = false;
            alternative.last_mavlink_ms = now_ms;
        }

        if (parsed_packet || i % 100 == 0) {
            // make sure we don't spend too much time parsing mavlink messages
            if (AP_HAL::micros() - tstart_us > max_time_us) {
                break;
            }
        }
    }

    const uint32_t tnow = AP_HAL::millis();

    // send a timesync message every 10 seconds; this is for data
    // collection purposes
    if (tnow - _timesync_request.last_sent_ms > _timesync_request.interval_ms) {
        if (HAVE_PAYLOAD_SPACE(chan, TIMESYNC)) {
            send_timesync();
            _timesync_request.last_sent_ms = tnow;
        }
    }

    if (!waypoint_receiving) {
        hal.util->perf_end(_perf_update);    
        return;
    }

    uint32_t wp_recv_time = 1000U + (stream_slowdown*20);

    // stop waypoint receiving if timeout
    if (waypoint_receiving && (tnow - waypoint_timelast_receive) > wp_recv_time+waypoint_receive_timeout) {
        waypoint_receiving = false;
    } else if (waypoint_receiving &&
               (tnow - waypoint_timelast_request) > wp_recv_time) {
        waypoint_timelast_request = tnow;
        send_message(MSG_NEXT_WAYPOINT);
    }

    hal.util->perf_end(_perf_update);    
}


/*
  send the SYSTEM_TIME message
 */
void GCS_MAVLINK::send_system_time()
{
    mavlink_msg_system_time_send(
        chan,
        AP::gps().time_epoch_usec(),
        AP_HAL::millis());
}


/*
  send RC_CHANNELS messages
 */
void GCS_MAVLINK::send_radio_in()
{
    AP_RSSI *rssi = AP::rssi();
    uint8_t receiver_rssi = 0;
    if (rssi != nullptr) {
        receiver_rssi = rssi->read_receiver_rssi_uint8();
    }

    uint32_t now = AP_HAL::millis();
    mavlink_status_t *status = mavlink_get_channel_status(chan);

    uint16_t values[18];
    RC_Channels::get_radio_in(values, 18);

    if (status && (status->flags & MAVLINK_STATUS_FLAG_OUT_MAVLINK1)) {
        // for mavlink1 send RC_CHANNELS_RAW, for compatibility with OSD implementations
        mavlink_msg_rc_channels_raw_send(
            chan,
            now,
            0,
            values[0],
            values[1],
            values[2],
            values[3],
            values[4],
            values[5],
            values[6],
            values[7],
            receiver_rssi);
    }
    if (!HAVE_PAYLOAD_SPACE(chan, RC_CHANNELS)) {
        // can't fit RC_CHANNELS
        return;
    }
    mavlink_msg_rc_channels_send(
        chan,
        now,
        RC_Channels::get_valid_channel_count(),
        values[0],
        values[1],
        values[2],
        values[3],
        values[4],
        values[5],
        values[6],
        values[7],
        values[8],
        values[9],
        values[10],
        values[11],
        values[12],
        values[13],
        values[14],
        values[15],
        values[16],
        values[17],
        receiver_rssi);        
}

void GCS_MAVLINK::send_raw_imu()
{
    const AP_InertialSensor &ins = AP::ins();
    const Compass &compass = AP::compass();

    const Vector3f &accel = ins.get_accel(0);
    const Vector3f &gyro = ins.get_gyro(0);
    Vector3f mag;
    if (compass.get_count() >= 1) {
        mag = compass.get_field(0);
    } else {
        mag.zero();
    }

    mavlink_msg_raw_imu_send(
        chan,
        AP_HAL::micros(),
        accel.x * 1000.0f / GRAVITY_MSS,
        accel.y * 1000.0f / GRAVITY_MSS,
        accel.z * 1000.0f / GRAVITY_MSS,
        gyro.x * 1000.0f,
        gyro.y * 1000.0f,
        gyro.z * 1000.0f,
        mag.x,
        mag.y,
        mag.z);

    if (ins.get_gyro_count() <= 1 &&
        ins.get_accel_count() <= 1 &&
        compass.get_count() <= 1) {
        return;
    }
    if (!HAVE_PAYLOAD_SPACE(chan, SCALED_IMU2)) {
        return;
    }
    const Vector3f &accel2 = ins.get_accel(1);
    const Vector3f &gyro2 = ins.get_gyro(1);
    if (compass.get_count() >= 2) {
        mag = compass.get_field(1);
    } else {
        mag.zero();
    }
    mavlink_msg_scaled_imu2_send(
        chan,
        AP_HAL::millis(),
        accel2.x * 1000.0f / GRAVITY_MSS,
        accel2.y * 1000.0f / GRAVITY_MSS,
        accel2.z * 1000.0f / GRAVITY_MSS,
        gyro2.x * 1000.0f,
        gyro2.y * 1000.0f,
        gyro2.z * 1000.0f,
        mag.x,
        mag.y,
        mag.z);        

    if (ins.get_gyro_count() <= 2 &&
        ins.get_accel_count() <= 2 &&
        compass.get_count() <= 2) {
        return;
    }
    if (!HAVE_PAYLOAD_SPACE(chan, SCALED_IMU3)) {
        return;
    }
    const Vector3f &accel3 = ins.get_accel(2);
    const Vector3f &gyro3 = ins.get_gyro(2);
    if (compass.get_count() >= 3) {
        mag = compass.get_field(2);
    } else {
        mag.zero();
    }
    mavlink_msg_scaled_imu3_send(
        chan,
        AP_HAL::millis(),
        accel3.x * 1000.0f / GRAVITY_MSS,
        accel3.y * 1000.0f / GRAVITY_MSS,
        accel3.z * 1000.0f / GRAVITY_MSS,
        gyro3.x * 1000.0f,
        gyro3.y * 1000.0f,
        gyro3.z * 1000.0f,
        mag.x,
        mag.y,
        mag.z);        
}

// sub overrides this to send on-board temperature
void GCS_MAVLINK::send_scaled_pressure3()
{
    const AP_Baro &barometer = AP::baro();

    if (barometer.num_instances() < 3) {
        return;
    }
    if (!HAVE_PAYLOAD_SPACE(chan, SCALED_PRESSURE3)) {
        return;
    }

    const float pressure = barometer.get_pressure(2);
    mavlink_msg_scaled_pressure3_send(
        chan,
        AP_HAL::millis(),
        pressure*0.01f, // hectopascal
        (pressure - barometer.get_ground_pressure(2))*0.01f, // hectopascal
        barometer.get_temperature(2)*100); // 0.01 degrees C
}

void GCS_MAVLINK::send_scaled_pressure()
{
    uint32_t now = AP_HAL::millis();
    const AP_Baro &barometer = AP::baro();
    float pressure = barometer.get_pressure(0);
    float diff_pressure = 0; // pascal

    AP_Airspeed *airspeed = AP_Airspeed::get_singleton();
    if (airspeed != nullptr) {
        diff_pressure = airspeed->get_differential_pressure();
    }

    mavlink_msg_scaled_pressure_send(
        chan,
        now,
        pressure*0.01f, // hectopascal
        diff_pressure*0.01f, // hectopascal
        barometer.get_temperature(0)*100); // 0.01 degrees C

    if (barometer.num_instances() > 1 &&
        HAVE_PAYLOAD_SPACE(chan, SCALED_PRESSURE2)) {
        pressure = barometer.get_pressure(1);
        mavlink_msg_scaled_pressure2_send(
            chan,
            now,
            pressure*0.01f, // hectopascal
            (pressure - barometer.get_ground_pressure(1))*0.01f, // hectopascal
            barometer.get_temperature(1)*100); // 0.01 degrees C        
    }

    send_scaled_pressure3();
}

void GCS_MAVLINK::send_sensor_offsets()
{
    const AP_InertialSensor &ins = AP::ins();
    const Compass &compass = AP::compass();

    // run this message at a much lower rate - otherwise it
    // pointlessly wastes quite a lot of bandwidth
    static uint8_t counter;
    if (counter++ < 10) {
        return;
    }
    counter = 0;

    const Vector3f &mag_offsets = compass.get_offsets(0);
    const Vector3f &accel_offsets = ins.get_accel_offsets(0);
    const Vector3f &gyro_offsets = ins.get_gyro_offsets(0);

    const AP_Baro &barometer = AP::baro();

    mavlink_msg_sensor_offsets_send(chan,
                                    mag_offsets.x,
                                    mag_offsets.y,
                                    mag_offsets.z,
                                    compass.get_declination(),
                                    barometer.get_pressure(),
                                    barometer.get_temperature()*100,
                                    gyro_offsets.x,
                                    gyro_offsets.y,
                                    gyro_offsets.z,
                                    accel_offsets.x,
                                    accel_offsets.y,
                                    accel_offsets.z);
}

void GCS_MAVLINK::send_ahrs()
{
    const AP_AHRS &ahrs = AP::ahrs();
    const Vector3f &omega_I = ahrs.get_gyro_drift();
    mavlink_msg_ahrs_send(
        chan,
        omega_I.x,
        omega_I.y,
        omega_I.z,
        0,
        0,
        ahrs.get_error_rp(),
        ahrs.get_error_yaw());
}

/*
    send a statustext text string to specific MAVLink bitmask
*/
void GCS::send_statustext(MAV_SEVERITY severity, uint8_t dest_bitmask, const char *text)
{
    if (dataflash_p != nullptr) {
        dataflash_p->Log_Write_Message(text);
    }

    // add statustext message to FrSky lib queue
    if (frsky_telemetry_p != NULL) {
        frsky_telemetry_p->queue_message(severity, text);
    }

    // filter destination ports to only allow active ports.
    statustext_t statustext{};
    statustext.bitmask = (GCS_MAVLINK::active_channel_mask()  | GCS_MAVLINK::streaming_channel_mask() ) & dest_bitmask;
    if (!statustext.bitmask) {
        // nowhere to send
        return;
    }

    statustext.msg.severity = severity;
    strncpy(statustext.msg.text, text, sizeof(statustext.msg.text));

    // The force push will ensure comm links do not block other comm links forever if they fail.
    // If we push to a full buffer then we overwrite the oldest entry, effectively removing the
    // block but not until the buffer fills up.
    _statustext_queue.push_force(statustext);

    // try and send immediately if possible
    service_statustext();

    AP_Notify *notify = AP_Notify::instance();
    if (notify) {
        notify->send_text(text);
    }
}

/*
    send a statustext message to specific MAVLink connections in a bitmask
 */
void GCS::service_statustext(void)
{
    // create bitmask of what mavlink ports we should send this text to.
    // note, if sending to all ports, we only need to store the bitmask for each and the string only once.
    // once we send over a link, clear the port but other busy ports bit may stay allowing for faster links
    // to clear the bit and send quickly but slower links to still store the string. Regardless of mixed
    // bitrates of ports, a maximum of _status_capacity strings can be buffered. Downside
    // is if you have a super slow link mixed with a faster port, if there are _status_capacity
    // strings in the slow queue then the next item can not be queued for the faster link

    if (_statustext_queue.empty()) {
        // nothing to do
        return;
    }

    for (uint8_t idx=0; idx<_status_capacity; ) {
        statustext_t *statustext = _statustext_queue[idx];
        if (statustext == nullptr) {
            break;
        }

        // try and send to all active mavlink ports listed in the statustext.bitmask
        for (uint8_t i=0; i<MAVLINK_COMM_NUM_BUFFERS; i++) {
            uint8_t chan_bit = (1U<<i);
            // logical AND (&) to mask them together
            if (statustext->bitmask & chan_bit) {
                // something is queued on a port and that's the port index we're looped at
                mavlink_channel_t chan_index = (mavlink_channel_t)(MAVLINK_COMM_0+i);
                if (HAVE_PAYLOAD_SPACE(chan_index, STATUSTEXT)) {
                    // we have space so send then clear that channel bit on the mask
                    mavlink_msg_statustext_send(chan_index, statustext->msg.severity, statustext->msg.text);
                    statustext->bitmask &= ~chan_bit;
                }
            }
        }

        if (statustext->bitmask == 0) {
            _statustext_queue.remove(idx);
        } else {
            // move to next index
            idx++;
        }
    }
}

void GCS::send_message(enum ap_message id)
{
    for (uint8_t i=0; i<num_gcs(); i++) {
        if (chan(i).initialised) {
            chan(i).send_message(id);
        }
    }
}

void GCS::retry_deferred()
{
    for (uint8_t i=0; i<num_gcs(); i++) {
        if (chan(i).initialised) {
            chan(i).retry_deferred();
        }
    }
    service_statustext();
}

void GCS::data_stream_send()
{
    for (uint8_t i=0; i<num_gcs(); i++) {
        if (chan(i).initialised) {
            chan(i).data_stream_send();
        }
    }
}

void GCS::update(void)
{
    for (uint8_t i=0; i<num_gcs(); i++) {
        if (chan(i).initialised) {
            chan(i).update();
        }
    }
}

void GCS::send_mission_item_reached_message(uint16_t mission_index)
{
    for (uint8_t i=0; i<num_gcs(); i++) {
        if (chan(i).initialised) {
            chan(i).mission_item_reached_index = mission_index;
            chan(i).send_message(MSG_MISSION_ITEM_REACHED);
        }
    }
}

void GCS::setup_uarts(AP_SerialManager &serial_manager)
{
    for (uint8_t i = 1; i < MAVLINK_COMM_NUM_BUFFERS; i++) {
        chan(i).setup_uart(serial_manager, AP_SerialManager::SerialProtocol_MAVLink, i);
    }
}

// report battery2 state
void GCS_MAVLINK::send_battery2()
{
    const AP_BattMonitor &battery = AP::battery();

    if (battery.num_instances() > 1) {
        int16_t current;
        if (battery.has_current(1)) {
            current = battery.current_amps(1) * 100; // 10*mA
        } else {
            current = -1;
        }
        mavlink_msg_battery2_send(chan, battery.voltage(1)*1000, current);
    }
}

/*
  handle a SET_MODE MAVLink message
 */
void GCS_MAVLINK::handle_set_mode(mavlink_message_t* msg)
{
    mavlink_set_mode_t packet;
    mavlink_msg_set_mode_decode(msg, &packet);

    const MAV_MODE _base_mode = (MAV_MODE)packet.base_mode;
    const uint32_t _custom_mode = packet.custom_mode;

    const MAV_RESULT result = _set_mode_common(_base_mode, _custom_mode);

    // send ACK or NAK
    mavlink_msg_command_ack_send_buf(msg, chan, MAVLINK_MSG_ID_SET_MODE, result);
}

/*
  code common to both SET_MODE mavlink message and command long set_mode msg
*/
MAV_RESULT GCS_MAVLINK::_set_mode_common(const MAV_MODE _base_mode, const uint32_t _custom_mode)
{
    MAV_RESULT result = MAV_RESULT_UNSUPPORTED;
    // only accept custom modes because there is no easy mapping from Mavlink flight modes to AC flight modes
    if (_base_mode & MAV_MODE_FLAG_CUSTOM_MODE_ENABLED) {
        if (set_mode(_custom_mode)) {
            result = MAV_RESULT_ACCEPTED;
        }
    } else if (_base_mode == (MAV_MODE)MAV_MODE_FLAG_DECODE_POSITION_SAFETY) {
        // set the safety switch position. Must be in a command by itself
        if (_custom_mode == 0) {
            // turn safety off (pwm outputs flow to the motors)
            hal.rcout->force_safety_off();
            result = MAV_RESULT_ACCEPTED;
        } else if (_custom_mode == 1) {
            // turn safety on (no pwm outputs to the motors)
            if (hal.rcout->force_safety_on()) {
                result = MAV_RESULT_ACCEPTED;
            }
        }
    }

    return result;
}

#if AP_AHRS_NAVEKF_AVAILABLE
/*
  send OPTICAL_FLOW message
 */
void GCS_MAVLINK::send_opticalflow(const OpticalFlow &optflow)
{
    // exit immediately if no optical flow sensor or not healthy
    if (!optflow.healthy()) {
        return;
    }

    // get rates from sensor
    const Vector2f &flowRate = optflow.flowRate();
    const Vector2f &bodyRate = optflow.bodyRate();

    const AP_AHRS &ahrs = AP::ahrs();
    float hagl = 0;
    if (ahrs.have_inertial_nav()) {
        if (!ahrs.get_hagl(hagl)) {
            return;
        }
    }

    // populate and send message
    mavlink_msg_optical_flow_send(
        chan,
        AP_HAL::millis(),
        0, // sensor id is zero
        flowRate.x,
        flowRate.y,
        bodyRate.x,
        bodyRate.y,
        optflow.quality(),
        hagl,  // ground distance (in meters) set to zero
        flowRate.x,
        flowRate.y);
}
#endif

/*
  send AUTOPILOT_VERSION packet
 */
void GCS_MAVLINK::send_autopilot_version() const
{
    uint32_t flight_sw_version;
    uint32_t middleware_sw_version = 0;
    uint32_t os_sw_version = 0;
    uint32_t board_version = 0;
    char flight_custom_version[MAVLINK_MSG_AUTOPILOT_VERSION_FIELD_FLIGHT_CUSTOM_VERSION_LEN]{};
    char middleware_custom_version[MAVLINK_MSG_AUTOPILOT_VERSION_FIELD_MIDDLEWARE_CUSTOM_VERSION_LEN]{};
    char os_custom_version[MAVLINK_MSG_AUTOPILOT_VERSION_FIELD_OS_CUSTOM_VERSION_LEN]{};
    uint16_t vendor_id = 0;
    uint16_t product_id = 0;
    uint64_t uid = 0;
    uint8_t  uid2[MAVLINK_MSG_AUTOPILOT_VERSION_FIELD_UID2_LEN] = {0};
    const AP_FWVersion &version = get_fwver();

    flight_sw_version = version.major << (8 * 3) | \
                        version.minor << (8 * 2) | \
                        version.patch << (8 * 1) | \
                        (uint32_t)(version.fw_type) << (8 * 0);

    if (version.fw_hash_str) {
        strncpy(flight_custom_version, version.fw_hash_str, sizeof(flight_custom_version) - 1);
        flight_custom_version[sizeof(flight_custom_version) - 1] = '\0';
    }

    if (version.middleware_hash_str) {
        strncpy(middleware_custom_version, version.middleware_hash_str, sizeof(middleware_custom_version) - 1);
        middleware_custom_version[sizeof(middleware_custom_version) - 1] = '\0';
    }

    if (version.os_hash_str) {
        strncpy(os_custom_version, version.os_hash_str, sizeof(os_custom_version) - 1);
        os_custom_version[sizeof(os_custom_version) - 1] = '\0';
    }

    mavlink_msg_autopilot_version_send(
        chan,
        hal.util->get_capabilities(),
        flight_sw_version,
        middleware_sw_version,
        os_sw_version,
        board_version,
        (uint8_t *)flight_custom_version,
        (uint8_t *)middleware_custom_version,
        (uint8_t *)os_custom_version,
        vendor_id,
        product_id,
        uid,
        uid2
    );
}


/*
  send LOCAL_POSITION_NED message
 */
void GCS_MAVLINK::send_local_position() const
{
    const AP_AHRS &ahrs = AP::ahrs();

    Vector3f local_position, velocity;
    if (!ahrs.get_relative_position_NED_home(local_position) ||
        !ahrs.get_velocity_NED(velocity)) {
        // we don't know the position and velocity
        return;
    }

    mavlink_msg_local_position_ned_send(
        chan,
        AP_HAL::millis(),
        local_position.x,
        local_position.y,
        local_position.z,
        velocity.x,
        velocity.y,
        velocity.z);
}

/*
  send VIBRATION message
 */
void GCS_MAVLINK::send_vibration() const
{
    const AP_InertialSensor &ins = AP::ins();

    Vector3f vibration = ins.get_vibration_levels();

    mavlink_msg_vibration_send(
        chan,
        AP_HAL::micros64(),
        vibration.x,
        vibration.y,
        vibration.z,
        ins.get_accel_clip_count(0),
        ins.get_accel_clip_count(1),
        ins.get_accel_clip_count(2));
}

void GCS_MAVLINK::send_named_float(const char *name, float value) const
{
    char float_name[MAVLINK_MSG_NAMED_VALUE_FLOAT_FIELD_NAME_LEN+1] {};
    strncpy(float_name, name, MAVLINK_MSG_NAMED_VALUE_FLOAT_FIELD_NAME_LEN);
    mavlink_msg_named_value_float_send(chan, AP_HAL::millis(), float_name, value);
}

void GCS_MAVLINK::send_home() const
{
    if (!HAVE_PAYLOAD_SPACE(chan, HOME_POSITION)) {
        return;
    }
    if (!AP::ahrs().home_is_set()) {
        return;
    }

    Location home = AP::ahrs().get_home();

    const float q[4] = {1.0f, 0.0f, 0.0f, 0.0f};
    mavlink_msg_home_position_send(
        chan,
        home.lat,
        home.lng,
        home.alt * 10,
        0.0f, 0.0f, 0.0f,
        q,
        0.0f, 0.0f, 0.0f,
        AP_HAL::micros64());
}

void GCS_MAVLINK::send_ekf_origin() const
{
    if (!HAVE_PAYLOAD_SPACE(chan, GPS_GLOBAL_ORIGIN)) {
        return;
    }
    Location ekf_origin;
    if (!AP::ahrs().get_origin(ekf_origin)) {
        return;
    }
    mavlink_msg_gps_global_origin_send(
        chan,
        ekf_origin.lat,
        ekf_origin.lng,
        ekf_origin.alt * 10,
        AP_HAL::micros64());
}

/*
  Send MAVLink heartbeat
 */
void GCS_MAVLINK::send_heartbeat() const
{
    mavlink_msg_heartbeat_send(
        chan,
        frame_type(),
        MAV_AUTOPILOT_ARDUPILOTMEGA,
        base_mode(),
        custom_mode(),
        system_status());
}

float GCS_MAVLINK::adjust_rate_for_stream_trigger(enum streams stream_num)
{
    // send at a much lower rate while handling waypoints and
    // parameter sends
    if ((stream_num != STREAM_PARAMS) && 
        (waypoint_receiving || _queued_parameter != nullptr)) {
        return 0.25f;
    }

    return 1.0f;
}

// are we still delaying telemetry to try to avoid Xbee bricking?
bool GCS_MAVLINK::telemetry_delayed() const
{
    uint32_t tnow = AP_HAL::millis() >> 10;
    if (tnow > telem_delay()) {
        return false;
    }
    if (chan == MAVLINK_COMM_0 && hal.gpio->usb_connected()) {
        // this is USB telemetry, so won't be an Xbee
        return false;
    }
    // we're either on the 2nd UART, or no USB cable is connected
    // we need to delay telemetry by the TELEM_DELAY time
    return true;
}


/*
  send SERVO_OUTPUT_RAW
 */
void GCS_MAVLINK::send_servo_output_raw()
{
    uint16_t values[16] {};
    if (in_hil_mode()) {
        for (uint8_t i=0; i<16; i++) {
            values[i] = SRV_Channels::srv_channel(i)->get_output_pwm();
        }
    } else {
        hal.rcout->read(values, 16);
    }
    for (uint8_t i=0; i<16; i++) {
        if (values[i] == 65535) {
            values[i] = 0;
        }
    }    
    mavlink_msg_servo_output_raw_send(
            chan,
            AP_HAL::micros(),
            0,     // port
            values[0],  values[1],  values[2],  values[3],
            values[4],  values[5],  values[6],  values[7],
            values[8],  values[9],  values[10], values[11],
            values[12], values[13], values[14], values[15]);
}


void GCS_MAVLINK::send_collision_all(const AP_Avoidance::Obstacle &threat, MAV_COLLISION_ACTION behaviour)
{
    for (uint8_t i=0; i<MAVLINK_COMM_NUM_BUFFERS; i++) {
        if ((1U<<i) & mavlink_active) {
            mavlink_channel_t chan = (mavlink_channel_t)(MAVLINK_COMM_0+i);
            if (comm_get_txspace(chan) >= MAVLINK_NUM_NON_PAYLOAD_BYTES + MAVLINK_MSG_ID_COLLISION) {
                mavlink_msg_collision_send(
                    chan,
                    MAV_COLLISION_SRC_ADSB,
                    threat.src_id,
                    behaviour,
                    threat.threat_level,
                    threat.time_to_closest_approach,
                    threat.closest_approach_z,
                    threat.closest_approach_xy
                    );
            }
        }
    }
}

void GCS_MAVLINK::send_accelcal_vehicle_position(uint32_t position)
{
    if (HAVE_PAYLOAD_SPACE(chan, COMMAND_LONG)) {
        mavlink_msg_command_long_send(
            chan,
            0,
            0,
            MAV_CMD_ACCELCAL_VEHICLE_POS,
            0,
            (float) position,
            0, 0, 0, 0, 0, 0);
    }
}


float GCS_MAVLINK::vfr_hud_airspeed() const
{
    AP_Airspeed *airspeed = AP_Airspeed::get_singleton();
    if (airspeed != nullptr && airspeed->healthy()) {
        return airspeed->get_airspeed();
    }
    // because most vehicles don't have airspeed sensors, we return a
    // different sort of speed estimate in the relevant field for
    // comparison's sake.
    return AP::gps().ground_speed();
}

float GCS_MAVLINK::vfr_hud_climbrate() const
{
    return -vfr_hud_velned.z;
}

void GCS_MAVLINK::send_vfr_hud()
{
    AP_AHRS &ahrs = AP::ahrs();

    // return values ignored; we send stale data
    ahrs.get_position(global_position_current_loc);
    ahrs.get_velocity_NED(vfr_hud_velned);

    float alt;
    if (vfr_hud_make_alt_relative()) {
        ahrs.get_relative_position_D_home(alt);
        alt = -alt;
    } else {
        alt = global_position_current_loc.alt / 100.0f;
    }
    mavlink_msg_vfr_hud_send(
        chan,
        vfr_hud_airspeed(),
        ahrs.groundspeed(),
        (ahrs.yaw_sensor / 100) % 360,
        vfr_hud_throttle(),
        alt,
        vfr_hud_climbrate());
}

/*
  handle a MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN command 

  Optionally disable PX4IO overrides. This is done for quadplanes to
  prevent the mixer running while rebooting which can start the VTOL
  motors. That can be dangerous when a preflight reboot is done with
  the pilot close to the aircraft and can also damage the aircraft
 */
MAV_RESULT GCS_MAVLINK::handle_preflight_reboot(const mavlink_command_long_t &packet, bool disable_overrides)
{
    if (is_equal(packet.param1,1.0f) || is_equal(packet.param1,3.0f)) {
        if (disable_overrides) {
#if CONFIG_HAL_BOARD == HAL_BOARD_PX4 || CONFIG_HAL_BOARD == HAL_BOARD_VRBRAIN
            // disable overrides while rebooting
            int px4io_fd = open("/dev/px4io", 0);
            if (px4io_fd >= 0) {
                // disable OVERRIDES so we don't run the mixer while
                // rebooting
                if (ioctl(px4io_fd, PWM_SERVO_SET_OVERRIDE_OK, 0) != 0) {
                    hal.console->printf("SET_OVERRIDE_OK failed\n");
                }
                if (ioctl(px4io_fd, PWM_SERVO_SET_OVERRIDE_IMMEDIATE, 0) != 0) {
                    hal.console->printf("SET_OVERRIDE_IMMEDIATE failed\n");
                }
                close(px4io_fd);
            }
#endif
        }

        // force safety on 
        hal.rcout->force_safety_on();
        hal.rcout->force_safety_no_wait();
        hal.scheduler->delay(200);

        // when packet.param1 == 3 we reboot to hold in bootloader
        bool hold_in_bootloader = is_equal(packet.param1,3.0f);
        hal.scheduler->reboot(hold_in_bootloader);
        return MAV_RESULT_ACCEPTED;
    }
    return MAV_RESULT_UNSUPPORTED;
}

/*
  handle a flight termination request
 */
MAV_RESULT GCS_MAVLINK::handle_flight_termination(const mavlink_command_long_t &packet)
{
    AP_AdvancedFailsafe *failsafe = get_advanced_failsafe();
    if (failsafe == nullptr) {
        return MAV_RESULT_UNSUPPORTED;
    }

    bool should_terminate = packet.param1 > 0.5f;

    if (failsafe->gcs_terminate(should_terminate, "GCS request")) {
        return MAV_RESULT_ACCEPTED;
    }
    return MAV_RESULT_FAILED;
}

/*
  handle a R/C bind request (for spektrum)
 */
MAV_RESULT GCS_MAVLINK::handle_rc_bind(const mavlink_command_long_t &packet)
{
    // initiate bind procedure. We accept the DSM type from either
    // param1 or param2 due to a past mixup with what parameter is the
    // right one
    if (!RC_Channels::receiver_bind(packet.param2>0?packet.param2:packet.param1)) {
        return MAV_RESULT_FAILED;
    }
    return MAV_RESULT_ACCEPTED;
}

uint64_t GCS_MAVLINK::timesync_receive_timestamp_ns() const
{
    uint64_t ret = _port->receive_time_constraint_us(PAYLOAD_SIZE(chan, TIMESYNC));
    if (ret == 0) {
        ret = AP_HAL::micros64();
    }
    return ret*1000LL;
}

uint64_t GCS_MAVLINK::timesync_timestamp_ns() const
{
    // we add in our own system id try to ensure we only consider
    // responses to our own timesync request messages
    return AP_HAL::micros64()*1000LL + mavlink_system.sysid;
}

/*
  return a timesync request
  Sends back ts1 as received, and tc1 is the local timestamp in usec
 */
void GCS_MAVLINK::handle_timesync(mavlink_message_t *msg)
{
    // decode incoming timesync message
    mavlink_timesync_t tsync;
    mavlink_msg_timesync_decode(msg, &tsync);

    if (tsync.tc1 != 0) {
        // this is a response to a timesync request
        if (tsync.ts1 != _timesync_request.sent_ts1) {
            // we didn't actually send the request.... or it's a
            // response to an ancient request...
            return;
        }
        const uint64_t round_trip_time_us = (timesync_receive_timestamp_ns() - _timesync_request.sent_ts1)*0.001f;
#if 0
        gcs().send_text(MAV_SEVERITY_INFO,
                        "timesync response sysid=%u (latency=%fms)",
                        msg->sysid,
                        round_trip_time_us*0.001f);
#endif
        DataFlash_Class *df = DataFlash_Class::instance();
        if (df != nullptr) {
            DataFlash_Class::instance()->Log_Write(
                "TSYN",
                "TimeUS,SysID,RTT",
                "s-s",
                "F-F",
                "QBQ",
                AP_HAL::micros64(),
                msg->sysid,
                round_trip_time_us
                );
        }
        return;
    }

    // create new timesync struct with tc1 field as system time in
    // nanoseconds.  The client timestamp is as close as possible to
    // the time we received the TIMESYNC message.
    mavlink_timesync_t rsync;
    rsync.tc1 = timesync_receive_timestamp_ns();
    rsync.ts1 = tsync.ts1;

    // respond with a timesync message
    mavlink_msg_timesync_send(
        chan,
        rsync.tc1,
        rsync.ts1
        );
}

/*
 * broadcast a timesync message.  We may get multiple responses to this request.
 */
void GCS_MAVLINK::send_timesync()
{
    _timesync_request.sent_ts1 = timesync_timestamp_ns();
    mavlink_msg_timesync_send(
        chan,
        0,
        _timesync_request.sent_ts1
        );
}

void GCS_MAVLINK::handle_statustext(mavlink_message_t *msg)
{
    DataFlash_Class *df = DataFlash_Class::instance();
    if (df == nullptr) {
        return;
    }

    mavlink_statustext_t packet;
    mavlink_msg_statustext_decode(msg, &packet);
    const uint8_t max_prefix_len = 20;
    const uint8_t text_len = MAVLINK_MSG_STATUSTEXT_FIELD_TEXT_LEN+1+max_prefix_len;
    char text[text_len] = { 'G','C','S',':'};
    uint8_t offset = strlen(text);

    if (msg->sysid != sysid_my_gcs()) {
        offset = hal.util->snprintf(text,
                                    max_prefix_len,
                                    "SRC=%u/%u:",
                                    msg->sysid,
                                    msg->compid);
    }

    memcpy(&text[offset], packet.text, MAVLINK_MSG_STATUSTEXT_FIELD_TEXT_LEN);

    df->Log_Write_Message(text);
}


void GCS_MAVLINK::handle_common_gps_message(mavlink_message_t *msg)
{
    AP::gps().handle_msg(msg);
}


void GCS_MAVLINK::handle_common_camera_message(const mavlink_message_t *msg)
{
    AP_Camera *camera = get_camera();
    if (camera == nullptr) {
        return;
    }

    switch (msg->msgid) {
    case MAVLINK_MSG_ID_DIGICAM_CONFIGURE:      // MAV ID: 202
        //deprecated.  Use MAV_CMD_DO_DIGICAM_CONFIGURE
        break;
    case MAVLINK_MSG_ID_DIGICAM_CONTROL:
        //deprecated.  Use MAV_CMD_DO_DIGICAM_CONTROL
        camera->control_msg(msg);
        break;
    default:
        break;
    }
}
MAV_RESULT GCS_MAVLINK::handle_command_camera(const mavlink_command_long_t &packet)
{
    AP_Camera *camera = get_camera();
    if (camera == nullptr) {
        return MAV_RESULT_UNSUPPORTED;
    }

    MAV_RESULT result = MAV_RESULT_FAILED;
    switch (packet.command) {
    case MAV_CMD_DO_DIGICAM_CONFIGURE:
        camera->configure(packet.param1,
                          packet.param2,
                          packet.param3,
                          packet.param4,
                          packet.param5,
                          packet.param6,
                          packet.param7);
        result = MAV_RESULT_ACCEPTED;
        break;
    case MAV_CMD_DO_DIGICAM_CONTROL:
        camera->control(packet.param1,
                        packet.param2,
                        packet.param3,
                        packet.param4,
                        packet.param5,
                        packet.param6);
        result = MAV_RESULT_ACCEPTED;
        break;
    case MAV_CMD_DO_SET_CAM_TRIGG_DIST:
        camera->set_trigger_distance(packet.param1);
        result = MAV_RESULT_ACCEPTED;
        break;
    default:
        result = MAV_RESULT_UNSUPPORTED;
        break;
    }
    return result;
}

// sets ekf_origin if it has not been set.
//  should only be used when there is no GPS to provide an absolute position
void GCS_MAVLINK::set_ekf_origin(const Location& loc)
{
    // check location is valid
    if (!check_latlng(loc)) {
        return;
    }

    AP_AHRS &ahrs = AP::ahrs();

    // check if EKF origin has already been set
    Location ekf_origin;
    if (ahrs.get_origin(ekf_origin)) {
        return;
    }

    if (!ahrs.set_origin(loc)) {
        return;
    }

    // log ahrs home and ekf origin dataflash
    ahrs.Log_Write_Home_And_Origin();

    // send ekf origin to GCS
    send_ekf_origin();
}

void GCS_MAVLINK::handle_set_gps_global_origin(const mavlink_message_t *msg)
{
    mavlink_set_gps_global_origin_t packet;
    mavlink_msg_set_gps_global_origin_decode(msg, &packet);

    // sanity check location
    if (!check_latlng(packet.latitude, packet.longitude)) {
        // silently drop the request
        return;
    }

    Location ekf_origin {};
    ekf_origin.lat = packet.latitude;
    ekf_origin.lng = packet.longitude;
    ekf_origin.alt = packet.altitude / 10;
    set_ekf_origin(ekf_origin);
}

/*
  handle a DATA96 message
 */
void GCS_MAVLINK::handle_data_packet(mavlink_message_t *msg)
{
#if HAL_RCINPUT_WITH_AP_RADIO
    mavlink_data96_t m;
    mavlink_msg_data96_decode(msg, &m);
    switch (m.type) {
    case 42:
    case 43: {
        // pass to AP_Radio (for firmware upload and playing test tunes)
        AP_Radio *radio = AP_Radio::instance();
        if (radio != nullptr) {
            radio->handle_data_packet(chan, m);
        }
        break;
    }
    default:
        // unknown
        break;
    }
#endif
}

void GCS_MAVLINK::handle_vision_position_delta(mavlink_message_t *msg)
{
    AP_VisualOdom *visual_odom = get_visual_odom();
    if (visual_odom == nullptr) {
        return;
    }
    visual_odom->handle_msg(msg);
}

void GCS_MAVLINK::handle_vision_position_estimate(mavlink_message_t *msg)
{
    mavlink_vision_position_estimate_t m;
    mavlink_msg_vision_position_estimate_decode(msg, &m);

    handle_common_vision_position_estimate_data(m.usec, m.x, m.y, m.z, m.roll, m.pitch, m.yaw,
                                                PAYLOAD_SIZE(chan, VISION_POSITION_ESTIMATE));
}

void GCS_MAVLINK::handle_global_vision_position_estimate(mavlink_message_t *msg)
{
    mavlink_global_vision_position_estimate_t m;
    mavlink_msg_global_vision_position_estimate_decode(msg, &m);

    handle_common_vision_position_estimate_data(m.usec, m.x, m.y, m.z, m.roll, m.pitch, m.yaw,
                                                PAYLOAD_SIZE(chan, GLOBAL_VISION_POSITION_ESTIMATE));
}

void GCS_MAVLINK::handle_vicon_position_estimate(mavlink_message_t *msg)
{
    mavlink_vicon_position_estimate_t m;
    mavlink_msg_vicon_position_estimate_decode(msg, &m);

    handle_common_vision_position_estimate_data(m.usec, m.x, m.y, m.z, m.roll, m.pitch, m.yaw,
                                                PAYLOAD_SIZE(chan, VICON_POSITION_ESTIMATE));
}

// there are several messages which all have identical fields in them.
// This function provides common handling for the data contained in
// these packets
void GCS_MAVLINK::handle_common_vision_position_estimate_data(const uint64_t usec,
                                                              const float x,
                                                              const float y,
                                                              const float z,
                                                              const float roll,
                                                              const float pitch,
                                                              const float yaw,
                                                              const uint16_t payload_size)
{
    // correct offboard timestamp to be in local ms since boot
    uint32_t timestamp_ms = correct_offboard_timestamp_usec_to_ms(usec, payload_size);
    
    // sensor assumed to be at 0,0,0 body-frame; need parameters for this?
    // or a new message 
    const Vector3f sensor_offset = {};
    const Vector3f pos = {
        x,
        y,
        z
    };
    Quaternion attitude;
    attitude.from_euler(roll, pitch, yaw); // from_vector312?
    const float posErr = 0; // parameter required?
    const float angErr = 0; // parameter required?
    const uint32_t reset_timestamp_ms = 0; // no data available

    AP::ahrs().writeExtNavData(sensor_offset,
                               pos,
                               attitude,
                               posErr,
                               angErr,
                               timestamp_ms,
                               reset_timestamp_ms);

    log_vision_position_estimate_data(usec, x, y, z, roll, pitch, yaw);
}

void GCS_MAVLINK::log_vision_position_estimate_data(const uint64_t usec,
                                                    const float x,
                                                    const float y,
                                                    const float z,
                                                    const float roll,
                                                    const float pitch,
                                                    const float yaw)
{
    DataFlash_Class::instance()->Log_Write("VISP", "TimeUS,RemTimeUS,PX,PY,PZ,Roll,Pitch,Yaw",
                                           "ssmmmrrr", "FF000000", "QQffffff",
                                           (uint64_t)AP_HAL::micros64(),
                                           (uint64_t)usec,
                                           (double)x,
                                           (double)y,
                                           (double)z,
                                           (double)roll,
                                           (double)pitch,
                                           (double)yaw);
}

void GCS_MAVLINK::handle_att_pos_mocap(mavlink_message_t *msg)
{
    mavlink_att_pos_mocap_t m;
    mavlink_msg_att_pos_mocap_decode(msg, &m);

    // sensor assumed to be at 0,0,0 body-frame; need parameters for this?
    const Vector3f sensor_offset = {};
    const Vector3f pos = {
        m.x,
        m.y,
        m.z
    };
    Quaternion attitude = Quaternion(m.q);
    const float posErr = 0; // parameter required?
    const float angErr = 0; // parameter required?
    const uint32_t timestamp_ms = m.time_usec * 0.001;
    const uint32_t reset_timestamp_ms = 0; // no data available

    AP::ahrs().writeExtNavData(sensor_offset,
                               pos,
                               attitude,
                               posErr,
                               angErr,
                               timestamp_ms,
                               reset_timestamp_ms);
   
    // calculate euler orientation for logging
    float roll;
    float pitch;
    float yaw;
    attitude.to_euler(roll, pitch, yaw);

    log_vision_position_estimate_data(m.time_usec, m.x, m.y, m.z, roll, pitch, yaw);
}

void GCS_MAVLINK::handle_command_ack(const mavlink_message_t* msg)
{
    AP_AccelCal *accelcal = AP::ins().get_acal();
    if (accelcal != nullptr) {
        accelcal->handleMessage(msg);
    }
}

/*
  handle messages which don't require vehicle specific data
 */
void GCS_MAVLINK::handle_common_message(mavlink_message_t *msg)
{
    switch (msg->msgid) {
    case MAVLINK_MSG_ID_COMMAND_ACK: {
        handle_command_ack(msg);
        break;
    }

    case MAVLINK_MSG_ID_SETUP_SIGNING:
        handle_setup_signing(msg);
        break;

    case MAVLINK_MSG_ID_PARAM_REQUEST_LIST:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_PARAM_SET:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_PARAM_REQUEST_READ:
        handle_common_param_message(msg);
        break;

    case MAVLINK_MSG_ID_SET_GPS_GLOBAL_ORIGIN:
        handle_set_gps_global_origin(msg);
        break;

    case MAVLINK_MSG_ID_DEVICE_OP_READ:
        handle_device_op_read(msg);
        break;
    case MAVLINK_MSG_ID_DEVICE_OP_WRITE:
        handle_device_op_write(msg);
        break;
    case MAVLINK_MSG_ID_TIMESYNC:
        handle_timesync(msg);
        break;
    case MAVLINK_MSG_ID_LOG_REQUEST_LIST:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_LOG_REQUEST_DATA:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_LOG_ERASE:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_LOG_REQUEST_END:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_REMOTE_LOG_BLOCK_STATUS:
        DataFlash_Class::instance()->handle_mavlink_msg(*this, msg);
        break;


    case MAVLINK_MSG_ID_DIGICAM_CONFIGURE:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_DIGICAM_CONTROL:
        handle_common_camera_message(msg);
        break;

    case MAVLINK_MSG_ID_SET_MODE:
        handle_set_mode(msg);
        break;

    case MAVLINK_MSG_ID_AUTOPILOT_VERSION_REQUEST:
        handle_send_autopilot_version(msg);
        break;

    case MAVLINK_MSG_ID_MISSION_WRITE_PARTIAL_LIST:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_REQUEST_LIST:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_COUNT:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_CLEAR_ALL:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_ITEM:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_ITEM_INT:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_REQUEST_INT:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_REQUEST:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_ACK:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_MISSION_SET_CURRENT:
        handle_common_mission_message(msg);
        break;

    case MAVLINK_MSG_ID_SERIAL_CONTROL:
        handle_serial_control(msg);
        break;

    case MAVLINK_MSG_ID_GPS_RTCM_DATA:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_GPS_INPUT:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_HIL_GPS:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_GPS_INJECT_DATA:
        handle_common_gps_message(msg);
        break;

    case MAVLINK_MSG_ID_STATUSTEXT:
        handle_statustext(msg);
        break;

    case MAVLINK_MSG_ID_LED_CONTROL:
        // send message to Notify
        AP_Notify::handle_led_control(msg);
        break;

    case MAVLINK_MSG_ID_PLAY_TUNE:
        // send message to Notify
        AP_Notify::handle_play_tune(msg);
        break;

    case MAVLINK_MSG_ID_RALLY_POINT:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_RALLY_FETCH_POINT:
        handle_common_rally_message(msg);
        break;

    case MAVLINK_MSG_ID_REQUEST_DATA_STREAM:
        handle_request_data_stream(msg);
        break;

    case MAVLINK_MSG_ID_DATA96:
        handle_data_packet(msg);
        break;        

    case MAVLINK_MSG_ID_VISION_POSITION_DELTA:
        handle_vision_position_delta(msg);
        break;

    case MAVLINK_MSG_ID_VISION_POSITION_ESTIMATE:
        handle_vision_position_estimate(msg);
        break;

    case MAVLINK_MSG_ID_GLOBAL_VISION_POSITION_ESTIMATE:
        handle_global_vision_position_estimate(msg);
        break;

    case MAVLINK_MSG_ID_VICON_POSITION_ESTIMATE:
        handle_vicon_position_estimate(msg);
        break;

    case MAVLINK_MSG_ID_ATT_POS_MOCAP:
        handle_att_pos_mocap(msg);
        break;
    }

}

void GCS_MAVLINK::handle_common_mission_message(mavlink_message_t *msg)
{
    AP_Mission *_mission = get_mission();
    if (_mission == nullptr) {
        return;
    }
    switch (msg->msgid) {
    case MAVLINK_MSG_ID_MISSION_WRITE_PARTIAL_LIST: // MAV ID: 38
    {
        handle_mission_write_partial_list(*_mission, msg);
        break;
    }

    // GCS has sent us a mission item, store to EEPROM
    case MAVLINK_MSG_ID_MISSION_ITEM:           // MAV ID: 39
    case MAVLINK_MSG_ID_MISSION_ITEM_INT:
    {
        if (handle_mission_item(msg, *_mission)) {
            DataFlash_Class::instance()->Log_Write_EntireMission(*_mission);
        }
        break;
    }

    // read an individual command from EEPROM and send it to the GCS
    case MAVLINK_MSG_ID_MISSION_REQUEST_INT:
    case MAVLINK_MSG_ID_MISSION_REQUEST:     // MAV ID: 40, 51
    {
        handle_mission_request(*_mission, msg);
        break;
    }

    case MAVLINK_MSG_ID_MISSION_SET_CURRENT:    // MAV ID: 41
    {
        handle_mission_set_current(*_mission, msg);
        break;
    }

    // GCS request the full list of commands, we return just the number and leave the GCS to then request each command individually
    case MAVLINK_MSG_ID_MISSION_REQUEST_LIST:       // MAV ID: 43
    {
        handle_mission_request_list(*_mission, msg);
        break;
    }

    // GCS provides the full number of commands it wishes to upload
    //  individual commands will then be sent from the GCS using the MAVLINK_MSG_ID_MISSION_ITEM message
    case MAVLINK_MSG_ID_MISSION_COUNT:          // MAV ID: 44
    {
        handle_mission_count(*_mission, msg);
        break;
    }

    case MAVLINK_MSG_ID_MISSION_CLEAR_ALL:      // MAV ID: 45
    {
        handle_mission_clear_all(*_mission, msg);
        break;
    }

    case MAVLINK_MSG_ID_MISSION_ACK:
        /* not used */
        break;
    }
}

void GCS_MAVLINK::handle_send_autopilot_version(const mavlink_message_t *msg)
{
    send_autopilot_version();
}

void GCS_MAVLINK::send_banner()
{
    // mark the firmware version in the tlog
    const AP_FWVersion &fwver = get_fwver();
    send_text(MAV_SEVERITY_INFO, fwver.fw_string);

    if (fwver.middleware_hash_str && fwver.os_hash_str) {
        send_text(MAV_SEVERITY_INFO, "PX4: %s NuttX: %s",
                  fwver.middleware_hash_str, fwver.os_hash_str);
    }

    // send system ID if we can
    char sysid[40];
    if (hal.util->get_system_id(sysid)) {
        send_text(MAV_SEVERITY_INFO, sysid);
    }
}


void GCS_MAVLINK::send_simstate() const
{
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
    SITL::SITL *sitl = AP::sitl();
    if (sitl == nullptr) {
        return;
    }
    sitl->simstate_send(get_chan());
#endif
}

MAV_RESULT GCS_MAVLINK::handle_command_preflight_set_sensor_offsets(const mavlink_command_long_t &packet)
{
    Compass *compass = get_compass();
    if (compass == nullptr) {
        return MAV_RESULT_UNSUPPORTED;
    }

    uint8_t compassNumber = -1;
    if (is_equal(packet.param1, 2.0f)) {
        compassNumber = 0;
    } else if (is_equal(packet.param1, 5.0f)) {
        compassNumber = 1;
    } else if (is_equal(packet.param1, 6.0f)) {
        compassNumber = 2;
    }
    if (compassNumber == (uint8_t) -1) {
        return MAV_RESULT_FAILED;
    }
    compass->set_and_save_offsets(compassNumber, packet.param2, packet.param3, packet.param4);
    return MAV_RESULT_ACCEPTED;
}

bool GCS_MAVLINK::calibrate_gyros()
{
    AP::ins().init_gyro();
    if (!AP::ins().gyro_calibrated_ok_all()) {
        return false;
    }
    AP::ahrs().reset_gyro_drift();
    return true;
}

MAV_RESULT GCS_MAVLINK::_handle_command_preflight_calibration_baro()
{
    // fast barometer calibration
    gcs().send_text(MAV_SEVERITY_INFO, "Updating barometer calibration");
    AP::baro().update_calibration();
    gcs().send_text(MAV_SEVERITY_INFO, "Barometer calibration complete");

    AP_Airspeed *airspeed = AP_Airspeed::get_singleton();
    if (airspeed != nullptr) {
        airspeed->calibrate(false);
    }

    return MAV_RESULT_ACCEPTED;
}

MAV_RESULT GCS_MAVLINK::_handle_command_preflight_calibration(const mavlink_command_long_t &packet)
{
    if (is_equal(packet.param1,1.0f)) {
        if (!calibrate_gyros()) {
            return MAV_RESULT_FAILED;
        }
        return MAV_RESULT_ACCEPTED;
    }

    if (is_equal(packet.param3,1.0f)) {
        return _handle_command_preflight_calibration_baro();
    }

    if (is_equal(packet.param5,1.0f)) {
        // start with gyro calibration
        if (!calibrate_gyros()) {
            return MAV_RESULT_FAILED;
        }
        // start accel cal
        AP::ins().acal_init();
        AP::ins().get_acal()->start(this);
        return MAV_RESULT_ACCEPTED;
    }

    if (is_equal(packet.param5,2.0f)) {
        if (!calibrate_gyros()) {
            return MAV_RESULT_FAILED;
        }
        float trim_roll, trim_pitch;
        if (!AP::ins().calibrate_trim(trim_roll, trim_pitch)) {
            return MAV_RESULT_FAILED;
        }
        // reset ahrs's trim to suggested values from calibration routine
        AP::ahrs().set_trim(Vector3f(trim_roll, trim_pitch, 0));
        return MAV_RESULT_ACCEPTED;
    }

    if (is_equal(packet.param5,4.0f)) {
        // simple accel calibration
        return AP::ins().simple_accel_cal();
    }

    return MAV_RESULT_UNSUPPORTED;
}

MAV_RESULT GCS_MAVLINK::handle_command_preflight_calibration(const mavlink_command_long_t &packet)
{
    if (hal.util->get_soft_armed()) {
        // *preflight*, remember?
        return MAV_RESULT_FAILED;
    }
    // now call subclass methods:
    return _handle_command_preflight_calibration(packet);
}

MAV_RESULT GCS_MAVLINK::handle_command_mag_cal(const mavlink_command_long_t &packet)
{
    Compass *compass = get_compass();
    if (compass == nullptr) {
        return MAV_RESULT_UNSUPPORTED;
    }
    return compass->handle_mag_cal_command(packet);
}

MAV_RESULT GCS_MAVLINK::handle_command_request_autopilot_capabilities(const mavlink_command_long_t &packet)
{
    if (!is_equal(packet.param1,1.0f)) {
        return MAV_RESULT_FAILED;
    }

    send_autopilot_version();

    return MAV_RESULT_ACCEPTED;
}


MAV_RESULT GCS_MAVLINK::handle_command_do_send_banner(const mavlink_command_long_t &packet)
{
    send_banner();
    return MAV_RESULT_ACCEPTED;
}

MAV_RESULT GCS_MAVLINK::handle_command_do_set_mode(const mavlink_command_long_t &packet)
{
    const MAV_MODE _base_mode = (MAV_MODE)packet.param1;
    const uint32_t _custom_mode = (uint32_t)packet.param2;

    return _set_mode_common(_base_mode, _custom_mode);
}

MAV_RESULT GCS_MAVLINK::handle_command_get_home_position(const mavlink_command_long_t &packet)
{
    if (!AP::ahrs().home_is_set()) {
        return MAV_RESULT_FAILED;
    }
    send_home();
    send_ekf_origin();

    return MAV_RESULT_ACCEPTED;
}

MAV_RESULT GCS_MAVLINK::handle_command_long_message(mavlink_command_long_t &packet)
{
    MAV_RESULT result = MAV_RESULT_FAILED;

    switch (packet.command) {

    case MAV_CMD_DO_SET_MODE:
        result = handle_command_do_set_mode(packet);
        break;

    case MAV_CMD_DO_SEND_BANNER:
        result = handle_command_do_send_banner(packet);
        break;

    case MAV_CMD_DO_START_MAG_CAL:
    case MAV_CMD_DO_ACCEPT_MAG_CAL:
    case MAV_CMD_DO_CANCEL_MAG_CAL: {
        result = handle_command_mag_cal(packet);
        break;
    }

    case MAV_CMD_START_RX_PAIR:
        result = handle_rc_bind(packet);
        break;

    case MAV_CMD_DO_DIGICAM_CONFIGURE:
        FALLTHROUGH;
    case MAV_CMD_DO_DIGICAM_CONTROL:
        FALLTHROUGH;
    case MAV_CMD_DO_SET_CAM_TRIGG_DIST:
        result = handle_command_camera(packet);
        break;

    case MAV_CMD_REQUEST_AUTOPILOT_CAPABILITIES: {
        result = handle_command_request_autopilot_capabilities(packet);
        break;
    }

    case MAV_CMD_PREFLIGHT_CALIBRATION:
        result = handle_command_preflight_calibration(packet);
        break;

    case MAV_CMD_PREFLIGHT_SET_SENSOR_OFFSETS: {
        result = handle_command_preflight_set_sensor_offsets(packet);
        break;
    }

    case MAV_CMD_GET_HOME_POSITION:
        result = handle_command_get_home_position(packet);
        break;

    case MAV_CMD_PREFLIGHT_STORAGE:
        if (is_equal(packet.param1, 2.0f)) {
            AP_Param::erase_all();
            send_text(MAV_SEVERITY_WARNING, "All parameters reset, reboot board");
            result= MAV_RESULT_ACCEPTED;
        }
        break;

    case MAV_CMD_DO_SET_SERVO:
        FALLTHROUGH;
    case MAV_CMD_DO_REPEAT_SERVO:
        FALLTHROUGH;
    case MAV_CMD_DO_SET_RELAY:
        FALLTHROUGH;
    case MAV_CMD_DO_REPEAT_RELAY:
        result = handle_servorelay_message(packet);
        break;

    case MAV_CMD_DO_FLIGHTTERMINATION:
        result = handle_flight_termination(packet);
        break;

    default:
        result = MAV_RESULT_UNSUPPORTED;
        break;
    }

    return result;
}

bool GCS_MAVLINK::try_send_compass_message(const enum ap_message id)
{
    Compass *compass = get_compass();
    if (compass == nullptr) {
        return true;
    }
    bool ret = true;
    switch (id) {
    case MSG_MAG_CAL_PROGRESS:
        compass->send_mag_cal_progress(chan);
        ret = true;;
        break;
    case MSG_MAG_CAL_REPORT:
        compass->send_mag_cal_report(chan);
        ret = true;
        break;
    default:
        ret = true;
        break;
    }
    return ret;
}

bool GCS_MAVLINK::try_send_mission_message(const enum ap_message id)
{
    AP_Mission *mission = get_mission();
    if (mission == nullptr) {
        return true;
    }

    bool ret = true;
    switch (id) {
    case MSG_CURRENT_WAYPOINT:
        CHECK_PAYLOAD_SIZE(MISSION_CURRENT);
        mavlink_msg_mission_current_send(chan, mission->get_current_nav_index());
        ret = true;
        break;
    case MSG_MISSION_ITEM_REACHED:
        CHECK_PAYLOAD_SIZE(MISSION_ITEM_REACHED);
        mavlink_msg_mission_item_reached_send(chan, mission_item_reached_index);
        ret = true;
        break;
    case MSG_NEXT_WAYPOINT:
        CHECK_PAYLOAD_SIZE(MISSION_REQUEST);
        queued_waypoint_send();
        ret = true;
        break;
    default:
        ret = true;
        break;
    }
    return ret;
}

void GCS_MAVLINK::send_hwstatus()
{
    mavlink_msg_hwstatus_send(
        chan,
        hal.analogin->board_voltage()*1000,
        0);
}

bool GCS_MAVLINK::try_send_gps_message(const enum ap_message id)
{
    bool ret = true;
    switch(id) {
    case MSG_SYSTEM_TIME:
        CHECK_PAYLOAD_SIZE(SYSTEM_TIME);
        send_system_time();
        ret = true;
        break;
    case MSG_GPS_RAW:
        CHECK_PAYLOAD_SIZE(GPS_RAW_INT);
        AP::gps().send_mavlink_gps_raw(chan);
        ret = true;
        break;
    case MSG_GPS_RTK:
        CHECK_PAYLOAD_SIZE(GPS_RTK);
        AP::gps().send_mavlink_gps_rtk(chan, 0);
        ret = true;
        break;
    case MSG_GPS2_RAW:
        CHECK_PAYLOAD_SIZE(GPS2_RAW);
        AP::gps().send_mavlink_gps2_raw(chan);
        ret = true;
        break;
    case MSG_GPS2_RTK:
        CHECK_PAYLOAD_SIZE(GPS2_RTK);
        AP::gps().send_mavlink_gps_rtk(chan, 1);
        ret = true;
        break;
    default:
        ret = true;
        break;
    }
    return ret;
}


bool GCS_MAVLINK::try_send_camera_message(const enum ap_message id)
{
    AP_Camera *camera = get_camera();
    if (camera == nullptr) {
        return true;
    }

    bool ret = true;
    switch(id) {
    case MSG_CAMERA_FEEDBACK:
        CHECK_PAYLOAD_SIZE(CAMERA_FEEDBACK);
        camera->send_feedback(chan);
        ret = true;
        break;
    default:
        ret = true;
        break;
    }
    return ret;
}

void GCS_MAVLINK::send_attitude() const
{
    const AP_AHRS &ahrs = AP::ahrs();
    const Vector3f omega = ahrs.get_gyro();
    mavlink_msg_attitude_send(
        chan,
        AP_HAL::millis(),
        ahrs.roll,
        ahrs.pitch,
        ahrs.yaw,
        omega.x,
        omega.y,
        omega.z);
}

int32_t GCS_MAVLINK::global_position_int_alt() const {
    return global_position_current_loc.alt * 10UL;
}
int32_t GCS_MAVLINK::global_position_int_relative_alt() const {
    float posD;
    AP::ahrs().get_relative_position_D_home(posD);
    posD *= -1000.0f; // change from down to up and metres to millimeters
    return posD;
}
void GCS_MAVLINK::send_global_position_int()
{
    AP_AHRS &ahrs = AP::ahrs();

    ahrs.get_position(global_position_current_loc); // return value ignored; we send stale data

    Vector3f vel;
    ahrs.get_velocity_NED(vel);

    mavlink_msg_global_position_int_send(
        chan,
        AP_HAL::millis(),
        global_position_current_loc.lat, // in 1E7 degrees
        global_position_current_loc.lng, // in 1E7 degrees
        global_position_int_alt(),       // millimeters above ground/sea level
        global_position_int_relative_alt(), // millimeters above ground/sea level
        vel.x * 100,                     // X speed cm/s (+ve North)
        vel.y * 100,                     // Y speed cm/s (+ve East)
        vel.z * 100,                     // Z speed cm/s (+ve Down)
        ahrs.yaw_sensor);                // compass heading in 1/100 degree
}

bool GCS_MAVLINK::try_send_message(const enum ap_message id)
{
    if (telemetry_delayed()) {
        return false;
    }

    bool ret = true;

    switch(id) {

    case MSG_ATTITUDE:
        CHECK_PAYLOAD_SIZE(ATTITUDE);
        send_attitude();
        break;

    case MSG_NEXT_PARAM:
        CHECK_PAYLOAD_SIZE(PARAM_VALUE);
        queued_param_send();
        ret = true;
        break;

    case MSG_HEARTBEAT:
        CHECK_PAYLOAD_SIZE(HEARTBEAT);
        last_heartbeat_time = AP_HAL::millis();
        send_heartbeat();
        break;

    case MSG_HWSTATUS:
        CHECK_PAYLOAD_SIZE(HWSTATUS);
        send_hwstatus();
        ret = true;
        break;

    case MSG_LOCATION:
        CHECK_PAYLOAD_SIZE(GLOBAL_POSITION_INT);
        send_global_position_int();
        break;

    case MSG_CURRENT_WAYPOINT:
        FALLTHROUGH;
    case MSG_MISSION_ITEM_REACHED:
        FALLTHROUGH;
    case MSG_NEXT_WAYPOINT:
        ret = try_send_mission_message(id);
        break;

    case MSG_MAG_CAL_PROGRESS:
        FALLTHROUGH;
    case MSG_MAG_CAL_REPORT:
        ret = try_send_compass_message(id);
        break;

    case MSG_BATTERY_STATUS:
        send_battery_status();
        break;

    case MSG_BATTERY2:
        CHECK_PAYLOAD_SIZE(BATTERY2);
        send_battery2();
        break;

    case MSG_EXTENDED_STATUS2:
        CHECK_PAYLOAD_SIZE(MEMINFO);
        send_meminfo();
        ret = true;
        break;

    case MSG_RANGEFINDER:
        CHECK_PAYLOAD_SIZE(RANGEFINDER);
        send_rangefinder_downward();
        ret = send_distance_sensor();
        ret = ret && send_proximity();
        break;

    case MSG_CAMERA_FEEDBACK:
        ret = try_send_camera_message(id);
        break;

    case MSG_GPS_RAW:
        FALLTHROUGH;
    case MSG_GPS_RTK:
        FALLTHROUGH;
    case MSG_GPS2_RAW:
        FALLTHROUGH;
    case MSG_GPS2_RTK:
        FALLTHROUGH;
    case MSG_SYSTEM_TIME:
        ret = try_send_gps_message(id);
        break;

    case MSG_LOCAL_POSITION:
        CHECK_PAYLOAD_SIZE(LOCAL_POSITION_NED);
        send_local_position();
        break;

    case MSG_POSITION_TARGET_GLOBAL_INT:
        CHECK_PAYLOAD_SIZE(POSITION_TARGET_GLOBAL_INT);
        send_position_target_global_int();
        break;

    case MSG_RADIO_IN:
        CHECK_PAYLOAD_SIZE(RC_CHANNELS_RAW);
        send_radio_in();
        break;

    case MSG_RAW_IMU1:
        CHECK_PAYLOAD_SIZE(RAW_IMU);
        send_raw_imu();
        break;

    case MSG_RAW_IMU2:
        CHECK_PAYLOAD_SIZE(SCALED_PRESSURE);
        send_scaled_pressure();
        break;

    case MSG_RAW_IMU3:
        CHECK_PAYLOAD_SIZE(SENSOR_OFFSETS);
        send_sensor_offsets();
        break;

    case MSG_SERVO_OUTPUT_RAW:
        CHECK_PAYLOAD_SIZE(SERVO_OUTPUT_RAW);
        send_servo_output_raw();
        break;

    case MSG_SIMSTATE:
        CHECK_PAYLOAD_SIZE(SIMSTATE);
        send_simstate();
        CHECK_PAYLOAD_SIZE(AHRS2);
        send_ahrs2();
        break;

    case MSG_AHRS:
        CHECK_PAYLOAD_SIZE(AHRS);
        send_ahrs();
        break;

    case MSG_VFR_HUD:
        CHECK_PAYLOAD_SIZE(VFR_HUD);
        send_vfr_hud();
        break;

    case MSG_VIBRATION:
        CHECK_PAYLOAD_SIZE(VIBRATION);
        send_vibration();
        break;

    default:
        // try_send_message must always at some stage return true for
        // a message, or we will attempt to infinitely retry the
        // message as part of send_message.
        // This message will be sent out at the same rate as the
        // unknown message, so should be safe.
        gcs().send_text(MAV_SEVERITY_DEBUG, "Sending unknown message (%u)", id);
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
        AP_HAL::panic("Sending unknown ap_message %u", id);
#endif
        ret = true;
        break;
    }

    return ret;
}

void GCS_MAVLINK::data_stream_send(void)
{
    if (waypoint_receiving) {
        // don't interfere with mission transfer
        return;
    }

    if (!hal.scheduler->in_delay_callback()) {
        // DataFlash_Class will not send log data if we are armed.
        DataFlash_Class::instance()->handle_log_send();
    }

    gcs().set_out_of_time(false);

    send_queued_parameters();

    if (gcs().out_of_time()) return;

    if (hal.scheduler->in_delay_callback()) {
        if (in_hil_mode()) {
            // in HIL we need to keep sending servo values to ensure
            // the simulator doesn't pause, otherwise our sensor
            // calibration could stall
            if (stream_trigger(STREAM_RAW_CONTROLLER)) {
                send_message(MSG_SERVO_OUT);
            }
            if (stream_trigger(STREAM_RC_CHANNELS)) {
                send_message(MSG_SERVO_OUTPUT_RAW);
            }
        }
        // send no other streams while in delay, just in case they
        // take way too long to run
        return;
    }

    for (uint8_t i=0; all_stream_entries[i].ap_message_ids != nullptr; i++) {
        const streams id = (streams)all_stream_entries[i].stream_id;
        if (!stream_trigger(id)) {
            continue;
        }
        const ap_message *msg_ids = all_stream_entries[i].ap_message_ids;
        for (uint8_t j=0; j<all_stream_entries[i].num_ap_message_ids; j++) {
            const ap_message msg_id = msg_ids[j];
            send_message(msg_id);
        }
        if (gcs().out_of_time()) {
            break;
        }
    }
}

/*
  correct an offboard timestamp in microseconds into a local timestamp
  since boot in milliseconds. This is a transport lag correction function, and works by assuming two key things:

   1) the data did not come from the future in our time-domain
   2) the data is not older than max_lag_ms in our time-domain

  It works by estimating the transport lag by looking for the incoming
  packet that had the least lag, and converging on the offset that is
  associated with that lag

  Return a value in milliseconds since boot (for use by the EKF)
 */
uint32_t GCS_MAVLINK::correct_offboard_timestamp_usec_to_ms(uint64_t offboard_usec, uint16_t payload_size)
{
    const uint32_t max_lag_us = 500*1000UL;
    uint64_t local_us;
    // if the HAL supports it then constrain the latest possible time
    // the packet could have been sent by the uart receive time and
    // the baudrate and packet size.
    uint64_t uart_receive_time = _port->receive_time_constraint_us(payload_size);
    if (uart_receive_time != 0) {
        local_us = uart_receive_time;
    } else {
        local_us = AP_HAL::micros64();
    }
    int64_t diff_us = int64_t(local_us) - int64_t(offboard_usec);

    if (!lag_correction.initialised ||
        diff_us < lag_correction.link_offset_usec) {
        // this message arrived from the remote system with a
        // timestamp that would imply the message was from the
        // future. We know that isn't possible, so we adjust down the
        // correction value
        lag_correction.link_offset_usec = diff_us;
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
        printf("link_offset_usec=%lld\n", (long long int)diff_us);
#endif
        lag_correction.initialised = true;
    }

    int64_t estimate_us = offboard_usec + lag_correction.link_offset_usec;
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
    if (estimate_us > (int64_t)local_us) {
        // this should be impossible, just check it under SITL
        printf("msg from future %lld\n", (long long int)(estimate_us - local_us));
    }
#endif

    if (estimate_us + max_lag_us < int64_t(local_us)) {
        // this implies the message came from too far in the past. Clamp the lag estimate
        // to assume the message had maximum lag
        estimate_us = local_us - max_lag_us;
        lag_correction.link_offset_usec = estimate_us - offboard_usec;
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
        printf("offboard timestammp too old %lld\n", (long long int)(local_us - estimate_us));
#endif
    }

    if (lag_correction.min_sample_counter == 0) {
        lag_correction.min_sample_us = diff_us;
    }
    lag_correction.min_sample_counter++;
    if (diff_us < lag_correction.min_sample_us) {
        lag_correction.min_sample_us = diff_us;
    }
    if (lag_correction.min_sample_counter == 200) {
        // we have 200 samples of the transport lag. To
        // account for long term clock drift we set the diff we will
        // use in future to this value
        lag_correction.link_offset_usec = lag_correction.min_sample_us;
        lag_correction.min_sample_counter = 0;
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
        printf("new link_offset_usec=%lld\n", (long long int)(lag_correction.min_sample_us));
#endif
    }
    
    return estimate_us / 1000U;
}

GCS &gcs()
{
    return *GCS::instance();
}