PX4-Autopilot/src/modules/mavlink/mavlink_command_sender.cpp

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/**
 * @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 vehicle_command_s &command, mavlink_channel_t channel)
{
	// commands > uint16 are PX4 internal only
	if (command.command >= vehicle_command_s::VEHICLE_CMD_PX4_INTERNAL_START) {
		return 0;
	}

	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_s *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_s 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_s *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_s *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 < MAVLINK_COMM_NUM_BUFFERS; ++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 < MAVLINK_COMM_NUM_BUFFERS; ++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.
			item->command.confirmation = ++item->num_sent_per_channel[channel];
			mavlink_msg_command_long_send_struct(channel, &item->command);

			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.
			item->command.confirmation = ++item->num_sent_per_channel[channel];
			mavlink_msg_command_long_send_struct(channel, &item->command);
			// 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();
}