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

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/**
 * @file mavlink_orb_subscription.cpp
 * uORB subscription implementation.
 *
 * @author Anton Babushkin <anton.babushkin@me.com>
 * @author Lorenz Meier <lorenz@px4.io>
 */

#include "mavlink_orb_subscription.h"

#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#include <px4_defines.h>
#include <uORB/uORB.h>

MavlinkOrbSubscription::MavlinkOrbSubscription(const orb_id_t topic, int instance) :
	next(nullptr),
	_topic(topic),
	_fd(-1),
	_instance(instance),
	_published(false),
	_subscribe_from_beginning(false),
	_last_pub_check(0)
{
}

MavlinkOrbSubscription::~MavlinkOrbSubscription()
{
	if (_fd >= 0) {
		orb_unsubscribe(_fd);
	}
}

orb_id_t
MavlinkOrbSubscription::get_topic() const
{
	return _topic;
}

int
MavlinkOrbSubscription::get_instance() const
{
	return _instance;
}

bool
MavlinkOrbSubscription::update(uint64_t *time, void *data)
{


	// TODO this is NOT atomic operation, we can get data newer than time
	// if topic was published between orb_stat and orb_copy calls.

	uint64_t time_topic;

	if (orb_stat(_fd, &time_topic)) {
		/* error getting last topic publication time */
		time_topic = 0;
	}

	if (update(data)) {
		/* data copied successfully */

		if (time_topic == 0 || (time_topic != *time)) {
			*time = time_topic;
			return true;

		} else {
			return false;
		}
	}

	return false;
}

bool
MavlinkOrbSubscription::update(void *data)
{
	if (!is_published()) {
		return false;
	}

	if (orb_copy(_topic, _fd, data)) {
		if (data != nullptr) {
			/* error copying topic data */
			memset(data, 0, _topic->o_size);
		}

		return false;
	}

	return true;
}

bool
MavlinkOrbSubscription::update_if_changed(void *data)
{
	bool prevpub = _published;

	if (!is_published()) {
		return false;
	}

	bool updated;

	if (orb_check(_fd, &updated)) {
		return false;
	}

	// If we didn't update and this topic did not change
	// its publication status then nothing really changed
	if (!updated && prevpub == _published) {
		return false;
	}

	return update(data);
}

bool
MavlinkOrbSubscription::is_published()
{
	// If we marked it as published no need to check again
	if (_published) {
		return true;
	}

	// Telemetry can sustain an initial published check at 10 Hz
	hrt_abstime now = hrt_absolute_time();

	if (now - _last_pub_check < 100000) {
		return false;
	}

	// We are checking now
	_last_pub_check = now;

	// We don't want to subscribe to anything that does not exist
	// in order to save memory and file descriptors.
	// However, for some topics like vehicle_command_ack, we want to subscribe
	// from the beginning in order not to miss the first publish respective advertise.
	if (!_subscribe_from_beginning && orb_exists(_topic, _instance)) {
		return false;
	}

	if (_fd < 0) {
		_fd = orb_subscribe_multi(_topic, _instance);
	}

	bool updated;
	orb_check(_fd, &updated);

	if (updated) {
		_published = true;
	}

	// topic may have been last published before we subscribed
	uint64_t time_topic = 0;

	if (!_published && orb_stat(_fd, &time_topic) == PX4_OK) {
		if (time_topic != 0) {
			_published = true;
		}
	}

	return _published;
}

void
MavlinkOrbSubscription::subscribe_from_beginning(bool from_beginning)
{
	_subscribe_from_beginning = from_beginning;
}