ExamplePrintFcn Module Documentation

Toolbox: Miscellaneous Utility Blocks

Introduction

One-line Description: Demonstrates how to call C language print functions via MATLAB Coder in a PX4 embedded environment, enabling the printing of Simulink input signal data to the PX4 Nuttx console terminal.

This module belongs to the Miscellaneous Utility Blocks library in the RflySim toolchain. It serves as an embedded code generation example module for secondary development of PX4 firmware, illustrating how to call external C functions during the process of generating embedded PX4 code from MATLAB/Simulink. The module utilizes coder.ceval() to invoke the C standard library printf() function, while incorporating target environment detection to ensure that printing operations are executed only when running on the PX4 embedded target, thereby avoiding interference with Simulink simulation.

The typical use case for this module is embedded-side debugging during PX4 flight control algorithm development. Developers can modify this example to customize the format and output method of debugging data to be printed, and finally view real-time debugging data of the flight control on the PX4 Nuttx console. Coupled with the code generation and firmware compilation workflow of the RflySim toolchain, this module enables direct integration of debugging print logic into the PX4 firmware, with the debug output displayed directly on the PX4 console terminal—facilitating developers’ localization of algorithmic issues during embedded runtime.

Port Descriptions

Input Ports (Inputs)

Port Name	Data Type	Dimension	Description
u1	double	1×1	First integer value to be printed, input from the Simulink model
u2	double	1×1	Second integer value to be printed, input from the Simulink model

Output Ports (Outputs)

This module has no output ports.

Parameter Configuration (Parameters)

This module has no configurable parameters.

Parameter Settings Description

None

Module Characteristics (Block Characteristics)

Characteristic	Value
Supported Data Types	double, single, int8, int16, int32, uint8, uint16, uint32
Direct Feedthrough	Yes
Sample Time	Inherited
Code Generation Support	Yes

Data Communication Protocol

This module does not involve network communication.

Related Modules

Module Name	Description
CpxInt32ToVehicle	Sends Simulink integer values to custom C code on the PX4 onboard side
VehicleDataToSimulink	Outputs values from custom C code on the PX4 onboard side to the Simulink simulation environment
GetPX4Time	Retrieves the current runtime time on the PX4 onboard side, in seconds
ReadAirframeParams	Reads a specified parameter value from the PX4 onboard parameter table
WriteAirframeParams	Writes a specified parameter value to the PX4 onboard parameter table
Px4GpioSet	Controls the GPIO pin level of the PX4 flight control hardware
Px4PwmOut	Sets the PWM output value for a specified channel on the PX4 flight control
SimplePx4FmuI2cRead	I2C reads data from external devices (FMU-side only)
SimplePx4FmuI2cWrite	I2C writes data to external devices (FMU-side only)
SaveInt32ToLog	Saves a specified 32-bit integer variable to the PX4 log file
SaveFloatToLog	Saves a specified single-precision floating-point variable to the PX4 log file
GetPx4LocalPosition	Reads the current local position and velocity estimate from PX4
GetPx4GlobalPosition	Reads the current global position and altitude estimate from PX4
GetPx4Attitude	Reads the current attitude estimate and angular velocity from PX4
GetPx4InputRC	Reads the RC receiver input data from PX4
SetPx4ActuatorOutput	Directly sets the PX4 actuator output values for custom mixing
SetPx4VehicleCmd	Sends a PX4 drone control command to the onboard flight controller
ViconDataSendToPX4	Sends pose data obtained from the simulation environment to PX4 for position fusion
OptiTrackDataSendToPX4	Sends actual pose data obtained from OptiTrack to PX4 for position fusion

Usage Example

For related usage examples, please refer to the following path:

[RflySim Installation Path]/RflySimAPIs/5.RflySimFlyCtrl/0.ApiExps/2.PSPOfficialExps/Readme.pdf

Please refer to Readme.pdf in the above path for complete example descriptions and operational steps.

Notes and Common Issues

• Initialization Order: This module takes effect only when generating embedded code and deploying it to the PX4 flight control hardware. It does not perform printing operations in the MATLAB/Simulink simulation environment; therefore, do not expect printing output from this module during the simulation phase.
• Data Type Matching: By default, the module passes input signals as integers to the printf function. To print other data types, the format string and input signal data type must be modified accordingly; otherwise, garbled output or memory access errors may occur.
• Printing Frequency Limitation: Avoid frequently calling this module to print data in high-frequency control loops. Excessively high printing frequency consumes Nuttx console bandwidth and may interfere with the normal execution of core flight control tasks.
• Code Generation Condition: The module restricts printing to the code generation phase via the condition strcmp(coder.target, 'rtw'). Do not remove this condition, or Simulink simulation will encounter errors.
• Output Viewing Method: Printed output appears only on the PX4 Nuttx console terminal. To view it, connect to the flight controller via serial port or simulation terminal; it will not appear in the MATLAB command window.

Changelog

• v4.10 (2024-08-13): Initial release. Provides an example function for printing Simulink input signals on the PX4 Nuttx embedded console, demonstrating the development method of calling C language printf() via coder.ceval().