mavlink_command_sender.cpp

Go to the documentation of this file.

/****************************************************************************
 *
 *   Copyright (c) 2017 PX4 Development Team. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name PX4 nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/**
 * @file mavlink_command_sender.cpp
 * Mavlink commands sender with support for retransmission.
 *
 * @author Julian Oes <julian@oes.ch>
 */

#include "mavlink_command_sender.h"
#include <px4_platform_common/log.h>

#define CMD_DEBUG(FMT, ...) PX4_LOG_NAMED_COND("cmd sender", _debug_enabled, FMT, ##__VA_ARGS__)

MavlinkCommandSender *MavlinkCommandSender::_instance = nullptr;
px4_sem_t MavlinkCommandSender::_lock;

void MavlinkCommandSender::initialize()
{
    px4_sem_init(&_lock, 1, 1);

    if (_instance == nullptr) {
        _instance = new MavlinkCommandSender();
    }
}

MavlinkCommandSender &MavlinkCommandSender::instance()
{
    return *_instance;
}

MavlinkCommandSender::~MavlinkCommandSender()
{
    px4_sem_destroy(&_lock);
}

int MavlinkCommandSender::handle_vehicle_command(const struct vehicle_command_s &command, mavlink_channel_t channel)
{
    lock();
    CMD_DEBUG("new command: %d (channel: %d)", command.command, channel);

    mavlink_command_long_t msg = {};
    msg.target_system = command.target_system;
    msg.target_component = command.target_component;
    msg.command = command.command;
    msg.confirmation = command.confirmation;
    msg.param1 = command.param1;
    msg.param2 = command.param2;
    msg.param3 = command.param3;
    msg.param4 = command.param4;
    msg.param5 = command.param5;
    msg.param6 = command.param6;
    msg.param7 = command.param7;
    mavlink_msg_command_long_send_struct(channel, &msg);

    bool already_existing = false;
    _commands.reset_to_start();

    while (command_item_t *item = _commands.get_next()) {
        if (item->timestamp_us == command.timestamp) {

            // We should activate the channel by setting num_sent_per_channel from -1 to 0.
            item->num_sent_per_channel[channel] = 0;
            already_existing = true;
            break;
        }
    }

    if (!already_existing) {

        command_item_t new_item;
        new_item.command = msg;
        new_item.timestamp_us = command.timestamp;
        new_item.num_sent_per_channel[channel] = 0;
        new_item.last_time_sent_us = hrt_absolute_time();
        _commands.put(new_item);
    }

    unlock();
    return 0;
}

void MavlinkCommandSender::handle_mavlink_command_ack(const mavlink_command_ack_t &ack,
        uint8_t from_sysid, uint8_t from_compid, uint8_t channel)
{
    CMD_DEBUG("handling result %d for command %d (from %d:%d)",
          ack.result, ack.command, from_sysid, from_compid);
    lock();

    _commands.reset_to_start();

    while (command_item_t *item = _commands.get_next()) {
        // Check if the incoming ack matches any of the commands that we have sent.
        if (item->command.command == ack.command &&
            (item->command.target_system == 0 || from_sysid == item->command.target_system) &&
            (item->command.target_component == 0 || from_compid == item->command.target_component) &&
            item->num_sent_per_channel[channel] != -1) {
            item->num_sent_per_channel[channel] = -2;   // mark this as acknowledged
            break;
        }
    }

    unlock();
}

void MavlinkCommandSender::check_timeout(mavlink_channel_t channel)
{
    lock();

    _commands.reset_to_start();

    while (command_item_t *item = _commands.get_next()) {
        if (hrt_elapsed_time(&item->last_time_sent_us) <= TIMEOUT_US) {
            // We keep waiting for the timeout.
            continue;
        }

        // Loop through num_sent_per_channel and check if any channel has receives an ack for this command
        // (indicated by the value -2). We avoid removing the command at the time of receiving the ack
        // as some channels might be lagging behind and will end up putting the same command into the buffer.
        bool dropped_command = false;

        for (unsigned i = 0; i < MAX_MAVLINK_CHANNEL; ++i) {
            if (item->num_sent_per_channel[i] == -2) {
                _commands.drop_current();
                dropped_command = true;
                break;
            }
        }

        if (dropped_command) {
            continue;
        }

        // The goal of this is to retry from all channels. Therefore, we keep
        // track of the retry count for each channel.
        //
        // When the first channel does a retry, the timeout is reset.
        // (e.g. all channel have done 2 retries, then channel 0 is called
        // and does retry number 3, and also resets the timeout timestamp).

        // First, we need to determine what the current max and min retry level
        // are because we can only level up, if all have caught up.
        // If num_sent_per_channel is at -1, the channel is inactive.
        int8_t max_sent = 0;
        int8_t min_sent = INT8_MAX;

        for (unsigned i = 0; i < MAX_MAVLINK_CHANNEL; ++i) {
            if (item->num_sent_per_channel[i] > max_sent) {
                max_sent = item->num_sent_per_channel[i];
            }

            if ((item->num_sent_per_channel[i] != -1) &&
                (item->num_sent_per_channel[i] < min_sent)) {
                min_sent = item->num_sent_per_channel[i];
            }
        }

        if (item->num_sent_per_channel[channel] < max_sent && item->num_sent_per_channel[channel] != -1) {
            // We are behind and need to do a retransmission.
            mavlink_msg_command_long_send_struct(channel, &item->command);
            item->num_sent_per_channel[channel]++;

            CMD_DEBUG("command %d sent (not first, retries: %d/%d, channel: %d)",
                  item->command.command,
                  item->num_sent_per_channel[channel],
                  max_sent,
                  channel);

        } else if (item->num_sent_per_channel[channel] == max_sent &&
               min_sent == max_sent) {

            // If the next retry would be above the needed retries anyway, we can
            // drop the item, and continue with other items.
            if (item->num_sent_per_channel[channel] + 1 > RETRIES) {
                CMD_DEBUG("command %d dropped", item->command.command);
                _commands.drop_current();
                continue;
            }

            // We are the first of a new retransmission series.
            mavlink_msg_command_long_send_struct(channel, &item->command);
            item->num_sent_per_channel[channel]++;
            // Therefore, we are the ones setting the timestamp of this retry round.
            item->last_time_sent_us = hrt_absolute_time();

            CMD_DEBUG("command %d sent (first, retries: %d/%d, channel: %d)",
                  item->command.command,
                  item->num_sent_per_channel[channel],
                  max_sent,
                  channel);

        } else {
            // We are already ahead, so this should not happen.
            // If it ever does, just ignore it. It will timeout eventually.
            continue;
        }
    }

    unlock();
}