mavlink_stream.cpp
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/****************************************************************************
*
* Copyright (c) 2014-2017 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_stream.cpp
* Mavlink messages stream implementation.
*
* @author Anton Babushkin <anton.babushkin@me.com>
* @author Lorenz Meier <lorenz@px4.io>
*/
#include <stdlib.h>
#include "mavlink_stream.h"
#include "mavlink_main.h"
MavlinkStream::MavlinkStream(Mavlink *mavlink) :
_mavlink(mavlink)
{
_last_sent = hrt_absolute_time();
}
/**
* Update subscriptions and send message if necessary
*/
int
MavlinkStream::update(const hrt_abstime &t)
{
update_data();
// If the message has never been sent before we want
// to send it immediately and can return right away
if (_last_sent == 0) {
// this will give different messages on the same run a different
// initial timestamp which will help spacing them out
// on the link scheduling
if (send()) {
_last_sent = hrt_absolute_time();
if (!_first_message_sent) {
_first_message_sent = true;
}
}
return 0;
}
// One of the previous iterations sent the update
// already before the deadline
if (_last_sent > t) {
return -1;
}
int64_t dt = t - _last_sent;
int interval = _interval;
if (!const_rate()) {
interval /= _mavlink->get_rate_mult();
}
// We don't need to send anything if the inverval is 0. send() will be called manually.
if (interval == 0) {
return 0;
}
const bool unlimited_rate = interval < 0;
// Send the message if it is due or
// if it will overrun the next scheduled send interval
// by 30% of the interval time. This helps to avoid
// sending a scheduled message on average slower than
// scheduled. Doing this at 50% would risk sending
// the message too often as the loop runtime of the app
// needs to be accounted for as well.
// This method is not theoretically optimal but a suitable
// stopgap as it hits its deadlines well (0.5 Hz, 50 Hz and 250 Hz)
if (unlimited_rate || (dt > (interval - (_mavlink->get_main_loop_delay() / 10) * 3))) {
// interval expired, send message
// If the interval is non-zero and dt is smaller than 1.5 times the interval
// do not use the actual time but increment at a fixed rate, so that processing delays do not
// distort the average rate. The check of the maximum interval is done to ensure that after a
// long time not sending anything, sending multiple messages in a short time is avoided.
if (send()) {
_last_sent = ((interval > 0) && ((int64_t)(1.5f * interval) > dt)) ? _last_sent + interval : t;
if (!_first_message_sent) {
_first_message_sent = true;
}
return 0;
} else {
return -1;
}
}
return -1;
}