Use Custom C or C++ Code in Stateflow Charts

You can call C and C++ code and use code libraries in your Stateflow^® charts by integrating custom C or C++ code into the chart. You can use custom code to:

• Access specialized algorithms.

• Reuse existing code libraries.

• Implement complex mathematical operations.

• Maintain consistency between simulation models and production code.

Integrate Custom C Code

This example shows how to use custom C code to define constants, variables, and functions that you can access in the chart.

For more information about integrating custom C++ code in your charts, see Access Custom C++ Code in Stateflow Charts.

This Stateflow chart calls a custom code function, custom_function. This function reads the chart input data signal and the local data threshold. It then compares their values, and returns one of three custom global constants named HIGH, MEDIUM, and LOW. Based on this return value, the chart determines state transitions and modifies the custom variable custom_var.

To see the custom code that this chart uses:

1. Open the Configuration Parameters dialog box.

2. Click the Simulation Target pane.

3. Select the Code Information tab.

The Include headers tab contains an #include statement that specifies the header file sf_custom_header.h. This file contains the definitions of three static global constants and the declarations for the variable custom_var and the function custom_function.

The Source files tab specifies the source file sf_custom_source.c. This file sets the initial value of custom_var to zero and defines the function custom_function.

These files are located in the same folder that contains the model. To access custom code files in a different folder, use relative path names. For more information, see Specify Paths to Source Files and Libraries.

When you simulate the model, Stateflow compiles the source file and the chart into a single S-function MEX file. The custom definitions appear at the top of the generated machine header file sf_custom_header.h, which allows all charts in the model to access the custom code during simulation.

Configure Custom Code

Specify Custom Code Settings for Simulation

The examples for specifying C source, header, and library files are based on this folder structure.

To configure your model to access custom code during simulation, follow these steps.

1. Open the Configuration Parameters dialog box. For information on how to do this, see Set Configuration Parameters by Using the Dialog Box (Simulink).

2. In the Simulation Target pane, in the Code Information tab, specify these parameters:

   • Include headers — Enter the code to include at the top of the generated model.h header file, which declares custom functions and data in the generated code. The code appears at the top of all generated source code files and is visible to all generated code. For example, use this parameter to enter #include and #define statements. When you include a custom header file, you must enclose the file name in double quotes. For more information, see Include headers (Simulink).

     Note

     • The code you specify in this parameter can include extern declarations of variables or functions, such as extern int x or extern void myfun(void). However, global variable or function definitions such as int x or void myfun(void) cause linking errors because the definitions appear multiple times in the source files of the generated code.

     

   • Include directories — Enter a list of the folder paths that contain custom header, source, and library files that you include either directly in the configuration parameters or indirectly in the compiled target. You can separate entries with newlines, commas, spaces, or semicolons. For more information, see Include directories (Simulink).

     

   • Source files — Enter a list of source files to compile and link into the target separated by newlines, commas, spaces, or semicolons. For more information, see Source files (Simulink).

     

   • Libraries — Enter a list of static libraries that contain custom object code to link into the target, separated by newlines, commas, spaces, or semicolons. For more information, see Libraries (Simulink).

     

   • Defines — Enter a space-separated list of preprocessor macro definitions to add to the generated code. For more information, see Defines (Simulink).

   • Compiler flags — Enter additional compiler flags to be added to the compiler command line when your custom code is compiled. For more information, see Compiler flags (Simulink).

   • Linker flags — Enter additional linker flags to be added to the linker command line when your custom code is linked. For more information, see Linker flags (Simulink).

3. Under Advanced parameters, check that Import custom code (Simulink) is selected. This parameter is enabled by default.

For information on setting simulation options by using the command-line API, see Set Configuration Parameters Programmatically.

Specify Custom Code Settings for Code Generation

To configure your model to access custom code for code generation, use the Code Generation > Custom Code pane of the Configuration Parameters dialog box. You can use the same custom code settings for code generation that you use for simulation or use unique custom code settings.

• To use the same custom code settings used for simulation, select Use the same custom code settings as Simulation Target. Specify the custom code settings in the Simulation Target pane as described in Specify Custom Code Settings for Simulation.

• To use unique custom code settings, clear Use the same custom code settings as Simulation Target. In the Code Information tab, specify custom code settings for code generation. For descriptions of the parameters in this tab, see Specify Custom Code Settings for Simulation.

For more information, see Use the same custom code settings as Simulation Target (Simulink Coder) and Integrate External Code by Using Model Configuration Parameters (Simulink Coder).

Call Custom Code Functions in States and Transitions

You can call custom code functions from the actions of any state or transition or from other functions in the chart.

To call a custom code function, use the signature specified by the function declaration in your header file. Include an argument value for each formal argument in the function signature.

return_val = function_name(arg1,arg2,...)

Custom Code Configuration

• If your model contains library charts, configure the custom code settings for each library model that contributes a chart to your model. For more information, see Configure Custom Code in Library Models.

• Charts that use MATLAB^® as the action language do not support #define statements in custom code. To share constants between your chart and your custom code, use static global constants instead of macros.

• Do not share fixed-point data between your custom code and your Stateflow chart.

Specify Paths to Source Files and Libraries

When you update your model or start the simulation, the model searches for source files and libraries in the following order:

1. Working folder. For more information, see Working folder (MATLAB Coder).

2. Model folder (if this folder is different from the working folder)

3. List of folders that you specify in the Include directories field

4. All folders on the MATLAB search path, excluding the toolbox folders

Guidelines for Relative Path Syntax

You can specify the location of your custom code by using paths relative to the model folder. For instance, suppose that, in the previous example, you store the source and header files for your custom code in the model folder subfolders CustomCode/SourceFiles and CustomCode/HeaderFiles. To access these files, use the Include directories parameter to specify the relative paths of the subfolders.

Alternatively, you can use relative pathnames to specify the header and source files individually:

• Under Include headers, enter this pathname.

  #include "./CustomCode/HeaderFiles/sf_custom_code_constants_vars_fcns_hdr.h"

• Under Source files, enter this pathname.

  ./CustomCode/HeaderFiles/sf_custom_code_constants_vars_fcns_src.c

When you construct relative paths for custom code, follow these syntax guidelines:

• To indicate the model folder as the starting point for the relative path, use ./pathname or .\pathname. To indicate its parent folder as the starting point for the relative path, use ../pathname or ..\pathname.

• Use forward slashes (/) or backward slashes (\) as file separators, regardless of the platform you are using.

• Enclose paths in double quotes ("...") if they contain nonstandard path characters such as spaces or hyphens (-).

• Enclose expressions with dollar signs ($...$) to:

  • Evaluate the expressions in the MATLAB workspace. For example, suppose that CustomCodeFolder is a variable that you define in the MATLAB workspace as "module1". If you specify your custom code files using the path name .\work\source\$CustomCodeFolder$, then the model searches for the custom code files in the folder .\work\source\module1.

  • Use MATLAB functions that generate paths to your custom code files. The functions must be on the MATLAB search path.

    For example, suppose that a function myFolderFcn returns the path to your custom code folder by running the command fileparts(mfilename('fullpath')). If you specify a custom code file using the path name $myFolderFcn$/myCustomFile, then the model searches for myCustomFile in the folder returned by myFolderFcn.