Custom Startup Script in UAV Toolbox Support Package for PX4 Autopilots

The Hardware Setup process of UAV Toolbox Support Package for PX4^® Autopilots contains a step that enables the usage of a custom startup script. This startup script, which needs to be copied to the micro-SD card to be mounted on the Pixhawk^® Series flight controllers, helps in:

Enabling or disabling the default PX4 modules as per the support package capabilities
Avoiding interference with other default PX4 controller modules
Preparing the PX4 Autopilot hardware to run the application generated by Simulink^®

For details about using this script, see Performing PX4 System Startup from SD Card.

Modules Enabled Using Custom Startup Script

The UAV Toolbox Support Package for PX4 Autopilots uses the custom startup script to enable some of the important modules.

The following table lists the modules that are enabled during the system startup from SD card.

PX4 Modules Enabled Using Custom Startup Script	Usage
uORB	Enables uORB message bus communication
px4io	Starts the firmware in IO processor of PX4 Autopilot and it is responsible for Main PWM Output
fmu	Generating AUX PWM outputs
ekf2	Estimator that outputs vehicle attitude
sensors	The sensors module reads the onboard sensors values and publishes data over uORB message bus
mtd and param	Loading and reading parameter
px4_simulink_app	The Simulink generated code that is integrated in PX4 Firmware as a separate module

Modules Disabled Using Custom Startup Script

The UAV Toolbox Support Package for PX4 Autopilots uses the custom startup script to disable few modules.

The following table lists few modules that are disabled at startup.

PX4 Modules Disabled at Startup	Reason for Disabling
Position Controller Attitude & Rate Controller	The support package enables you to design the controller and hence the default Controller module in PX4 is disabled.
Commander	The default Commander module is disabled to avoid possible interference with controller algorithm
Navigator	The default Navigator module is disabled to avoid possible interference with controller algorithm
MAVLink	The default serial port of MAVLink communication is the USB port of PX4 Autopilot. The MAVLink modules are disabled during startup to enable out-of-the-box External Mode support from Simulink, which uses the same USB port.

However, you can enable MAVLink while configuring the Simulink model. For details, see Enabling MAVLink in PX4 Over USB.

To understand the impact of disabling the modules, see Impact of Disabling MAVLink, Commander, and Navigator Modules.