timeout is an int, so it wraps when the poll timeout is >2147ms.
This happened in logger, resulting in poll never returning.

For now we need to ignore this warning which GCC 9 shows for the MAVLink
headers.

GCC 9 complained about stringop-truncation which is a cautionary message
to prevent using strncpy with non-null terminated strings.

We can fix this by copying one byte less than the destination size and
then manually adding the null termination, as we already do.

visibility.h is included globally in PX4 via cmake compile flags.
It contains poisoning the exit() command which is used by gtest
to close the test application. Removing the flag for gtest compilation
fixes the compile error:
gtest.cc:4757:7: error: attempt to use poisoned "exit"

* VTOL trans: changed that now in transition for both MC and FW the corresponding (correct) attitude controller is running
* attitude setpoint for stabilized mode is generated by tailsitter.cpp
* reset yaw setpoint during transition to avoid big yaw errors after
transition back to hover
* VT_TYPE parameter: added "reboot required" metadata

    - ecl in PX4/Firmware (fa1fbed24633aef7985a128ebd4d19a7f6a4d108): https://github.com/PX4/ecl/commit/c4492b17c1d7bb9b74011efa9890452b091421e8
    - ecl current upstream: https://github.com/PX4/ecl/commit/a27a43eafa8f4dd514e89984f5394260a36ea4f6
    - Changes: https://github.com/PX4/ecl/compare/c4492b17c1d7bb9b74011efa9890452b091421e8...a27a43eafa8f4dd514e89984f5394260a36ea4f6

a27a43e 2019-05-01 Hamish Willee - Fix up link to EKF docs
3f69189 2019-04-04 Mohammed Kabir - EKF: control: stop vision yaw fusion on timeout

Commander initially publishes a tune_control topic set to 0, which can
interfere with the startup tone (as happening on the Pixhawk Cube).

To be able to still infer the direction of the thrust vector we
limit it to a minimal length even if MPC_THR_MIN is set to zero.

Note: This is a hotfix for certain specific applications.
The direction of the thrust vector in this corner case is very
likely to get into the tilt limit which is generally undesired.

A low gyro cutoff is needed for most medium/large size drones as the structural natural and blade-pass frequencies are low.
A higher value is still desirable for small platforms surch as racers
or well isolated autopilots and should be tuned by the user.
Specific values for config files are untouched.
The cutoff filter for the D term is disabled here as the required
cutoff frequency for the default D term of the rate controller is higher
than the gyro cutoff. In that case, enabling the D term cutoff would
just add some undesired phase lag to the derivative.

It looks like the atomic builtins are not available using QuRT and the
Hexagon toolchain, so our best bet is to use `volatile` for the atomics.

This fixes a potential dead-lock when 'uorb status' was used via MAVLink
shell.
The dead-lock chain is: DeviceMaster::lock() -> printf -> output to a pipe,
which blocks until a reader reads the data. In that case it's mavlink.
If mavlink makes a call that requires DeviceMaster::lock() (such as
orb_exists), it dead-locks.

This patch moves all printf's out of the locked state.

- when either terrain data was temporarily not valid (flying at high
distance to the ground) or the vehicle was not close to the ground
(_param_ekf2_gnd_max_hgt) the ekf switched to using the land detector
ground effect flag.

Signed-off-by: Roman <bapstroman@gmail.com>

- takeoff help is used for fixed wings, it increases the altitude setpoint
after a launch. A vtol does not need this as it's already sufficiently
high up in the air.

Signed-off-by: Roman <bapstroman@gmail.com>

This reverts commit 4a71984f.

The noise for airspeed is now applied on the Gazebo side and we can
remove this hack.

the condition to enter the rc mode switch evaluation was neglecting
the first connection of an RC when "no RC switch changed". this means
depending on the actual initialization values of _last_sp_man and the
desired mode preselected on the RC while connecting it would not get
evaluated.

pure refactor using De Morgan's law to make the condition more intuitive
since you think about when should I enter and not when should I skip

pure refactor of the huge condition into smaller const bool junks

There were multiple comments not addressed in pr #11904.
See commit 4bcb37f9bc9ef20b521ebcf33e7a0ed08fa86ccd

The Pixhawk cube as an internal mag on SPI. If there was a bad register
read (e.g. on an IMU failure), _register_wait was non-zero and there was
no transfer but _mag still published mpu_report.mag.

Auto mode traj - limit yaw setpoint rate of change when generated in the flight task instead of clamping the yaw rate in the controller

Move yaw setpoint slew rate from AutoLineSmoothVel to Auto. The slew rate is now applied consistently to all the auto FlightTasks

Add missing underscore prefix to a member variable in mavlink_main.cpp.h and delete unnecessary struct specifiers in mavlink_main.h.