- nuttx in PX4/Firmware (0a1a2025402a387cde88132c6f8d8cc7237d2e6b): https://github.com/PX4-NuttX/nuttx/commit/bf8cce85c3f9310bcff8cdd1d979270419782a6e
    - nuttx current upstream: https://github.com/PX4-NuttX/nuttx/commit/e3b5b667aee16a699ecd6605f2d2a4adc6e95c17
    - Changes: https://github.com/PX4-NuttX/nuttx/compare/bf8cce85c3f9310bcff8cdd1d979270419782a6e...e3b5b667aee16a699ecd6605f2d2a4adc6e95c17

e3b5b66 2018-08-31 Daniel Agar - [BACKPORT] Merged in dagar/nuttx/pr-stm32f7_stackcheck-upstream (pull request #714)

 - The first waypoint contains the vehicle current position and the desired velocity setpoint

  Use CONFIG_ARMV7M_STACKCHECK to add the instrumentation
  for runtime stack checking

  To enable coherent runtime stack checking use the boards
  CONFIG_ARMV7M_STACKCHECK setting

 - this is shared by both the FW position controller and navigator's
   missiong feasibility checker

Not needed anymore

This is all done through posix_sitl_default.cmake and env variables:
- PX4_ESTIMATOR
- replay

Generally exit() should not be used on Posix, because it exits the whole
program instead of only the task.

On POSIX it exits the process.

   On FW with a px4io bin file, but not a px4io do not error

   Use tune control and have all paths in rcS indicate tunes

    Adds a single file definition to provide a single point to add
    new tunes and clearly understand, the useage: it need to be
    stopped will it not allow interruption.

	Refactor to use the tune_control interface

    Since tune control came in this driver does not have a
    have a test based interface. The module Documentation
    has been moved to tune_control

    minor cleanup and assert on workque delay of 0

    Since tune control came in this driver does not have a
    have a test based interface. The module Documentation
    has been moved to tune_control

    Since tune control came in this driver does not have a
    have a test based interface. The module Documentation
    has been moved to tune_control

    minor cleanup and assert on workque delay of 0

    Since tune control came in this driver does not have a
    have a test based interface. The module Documentation
    has been moved to tune_control