Call Reusable External Algorithm Code for Simulation and Code Generation

Code reuse offers business and technological advantages. From a business perspective, code reuse saves time and resources. From a technological perspective, code reuse promotes consistency and reduces memory requirements. Other considerations include:

Modularizing an application
Reusing an optimized algorithm
Interfacing with a predefined dataset
Developing application variants

Examples of reusable hardware-independent algorithmic code to consider importing into the Simulink^® environment for simulation and code generation include:

Utility functions
Lookup tables
Digital filters
Specialized integrators
Proportional-integral-derivative (PID) control modules

Workflow

To call reusable external algorithm code for simulation and code generation, iterate through the tasks listed in this table.

Task	Action	More Information
1	Review your assessment of external code characteristics and integration requirements.	Choose an External Code Integration Workflow
2	Based on the programming language of the external code, choose an integration approach to add the external code to a Simulink model.	Choose an Integration Approach
3	Verify algorithm behavior and performance by simulating the model.	Simulation
4	Define the representation of model data for code generation.	Code Interface Configuration and Exchange Data Between External C/C++ Code and Simulink Model or Generated Code (Embedded Coder)
5	Configure the model for code generation.	Generate Code That Matches Appearance of External Code (Embedded Coder)
6	Generate code and a code generation report.	Code Generation
7	Review the generated code interface and static code metrics.	Analyze Generated Data Code Interface Report
8	Build an executable program from the model.	Build Integrated Code Within the Simulink Environment
9	Verify that executable program behaves as expected.	Verification and Testing

Choose an Integration Approach

Several approaches are available for integrating reusable algorithmic code into the Simulink environment for code generation. Some approaches integrate external code directly. Other approaches convert the external code to Simulink or Stateflow^® modeling elements for simulation, and later for code generation from the modeled design. The integration approach that you choose depends on:

Programming language of the external code — MATLAB^®, C, C++, or Fortran
Your programming language experience and preference
Performance requirements
Whether the algorithm must model continuous time dynamics or you are integrating the algorithm into an application that uses discrete and continuous time
Whether you want to take advantage of Model-Based Design
Level of control required over the code that the code generator produces

To choose an approach for a reusable algorithm, see the subsection that matches the programming language of your external algorithm code.

Integration Approaches for External MATLAB Code

Multiple approaches are available for integrating external MATLAB code into the Simulink environment. The following table helps you choose the best integration approach for your application based on integration requirements.

Condition or Requirement	Action	More Information
External code complies with the MATLAB code generation subset You want to call MATLAB code from a Simulink model	Add a MATLAB Function block to the model. Embed the MATLAB code in that block.	Integrate C Code by Using the MATLAB Function Block MATLAB Function
External code complies with the MATLAB code generation subset You want to call MATLAB code from a Simulink model Your algorithm includes iterative computations that process large streams of data	Add a MATLAB System block to the model. Embed the MATLAB code in that block as a System object™.	Integrate C Code by Using the MATLAB Function Block MATLAB System
External code complies with the MATLAB code generation subset You want to call MATLAB code from a Simulink model Your algorithm includes design logic that is based on state machines and flow charts	Add a Stateflow chart to the model. Call the external code from the chart, using MATLAB as the action language.	Chart Programming Basics (Stateflow) Insert External Code into Stateflow Charts
You want to use the `parfor` function for parallel computing or interface data types that are available to MATLAB Coder™, Simulink Coder, and Embedded Coder^®. To use `parfor`, Parallel Computing Toolbox™ must be installed.	Use software to generate C code. Then, call that generated code as external C code.	Generate C Code by Using the MATLAB Coder App Get Started with MATLAB Coder
You have C or C++ programming experience and the external MATLAB code is compact and primarily uses C or C++ constructs.	Manually convert the MATLAB code to C or C++ code. Choose an integration approach for C or C++ code.	Integration Approaches for External C or C++ Code
Sections of the external MATLAB code map to built-in blocks.	Develop the algorithm in the context of a model, using the applicable built-in blocks.	Interactive Model Editing and Project Management Use Products and Blocks Supported for Code Generation
The algorithm must model continuous state dynamics.	Write a MATLAB S-function and, for generating code, a corresponding TLC file for the algorithm. Add the S-function to your model.	Author Blocks Using MATLAB S-Functions Code Generation for Custom Blocks Target Language Compiler Target Language Compiler (Embedded Coder)

To embed external MATLAB code in a MATLAB Function block or generate C or C++ code from MATLAB code with the MATLAB Coder software, the MATLAB code must use functions and classes supported for C/C++ code generation.

Functions and Objects Supported for C/C++ Code Generation

Integration Approaches for External C or C++ Code

Multiple approaches are available for integrating external C or C++ code into the Simulink environment. The following table helps you choose the best integration approach for your application based on integration requirements.

Condition or Requirement	Action	More Information
You want to integrate external C code with generated C++ code or conversely	Match the language choice for the generated code by modifying the language of the external code.	Modify Programming Language of External Code to Match Generated Code
You have existing C code that models custom functionality. You want to integrate the code into Simulink blocks. Your functions do not read or write global/static variables. You want to easily integrate with Simulink Coverage™, Simulink Test™, and Simulink Design Verifier™	For simple algorithms written in C, consider using the Simulink C Caller block.	Integrate C Code Using C Caller Blocks
You have existing C code that models custom functionality. You want to call multiple C functions from a Simulink block, or call C functions conditionally. You want to include C code to preprocess and postprocess data before and after calling C functions. You want to specify different code for simulation and code generation.	Add a C Function block to your model.	Integrate C Code by Using the MATLAB Function Block
The algorithm must model discrete and continuous state dynamics for simulation and rapid prototyping. The external code requires a fixed-point interface. Programming experience is limited. You want ease of use with basic flexibility for controlling what code the code generator produces for rapid prototyping.	Generate S-function and TLC files by using the S-Function Builder. If necessary, refine the generated code manually to meet application requirements. (If you change the generated code, you lose the changes if you regenerate the S-function and TLC files.)	Use a Bus with S-Function Builder to Create an S-Function
You want to simulate and generate external code for a discrete time application. Optimizing generated code is essential. You want ease of use with moderate flexibility for controlling what code the code generator produces. You have C or C++ programming experience, but you prefer to generate the files for adding the code to a model.	Generate S-function and TLC files by using the Legacy Code Tool. If necessary, refine the generated code manually to meet application requirements. (If you change the generated code, you lose the changes if you regenerate the S-function and TLC files.)	Integrate C Functions Using Legacy Code Tool Import Calls to External Code into Generated Code with Legacy Code Tool Integrate C Code Using C Caller Blocks
The application requires more entry-point functions than the code generator typically produces—for example, more than `model_step`, `model_initialize`, and `model_terminate`. You want maximum flexibility for controlling what code the code generator produces.	Manually write an S-function and TLC file.	C/C++ S-Function Basics S-Functions and Code Generation C S-Function Examples and C++ S-Function Examples
Your algorithm includes design logic that is based on state machines and flow charts. Or, a function that you want to integrate must exchange data with a model by using global variables. The function defines the global variables and uses them to write output rather than returning a value (return) or writing output to an argument.	Add a Stateflow chart to the model. Call the external code from the chart, using C as the action language. In the chart, write code that calls the external function and reads from and writes to the global variables. To perform calculations with output of the external code, the model must read from the global variable during execution.	Insert External Code into Stateflow Charts
You want to include external C or C++ code in a Stateflow chart for simulation and code generation.	Configure the model that contains the chart to apply the external C or C++ code.	Custom Code (Stateflow) Call C Library Functions in C Charts (Stateflow) Insert External Code into Stateflow Charts
You quickly want to embed a call to external C or C++ code in a model. Performance is not an issue.	Call the C or C++ code with the `coder.ceval` function from within a MATLAB Function block.	`coder.ceval` function Integrate C Code by Using the MATLAB Function Block MATLAB Function block

Modify Programming Language of External Code to Match Generated Code

To integrate external C code with generated C++ code or conversely, modify the language of the external code to match the programming language choice for the generated code. Options for making the programming language match include:

Writing or rewriting the external code in the language choice for the generated code.
If you are generating C++ code and the external code is C code, for each C function, create a header file that prototypes the function. Use this format:
```
#ifdef __cplusplus
extern "C" {
#endif
int my_c_function_wrapper();
#ifdef __cplusplus
}
#endif
```
The prototype serves as a function wrapper. If your compiler supports C++ code, the value __cplusplus is defined. The linkage specification extern "C" specifies C linkage without name mangling.
If you are generating C code and the external code is C++ code, include an extern "C" linkage specification in each .cpp file. For example, the following example shows C++ code in the file my_func.cpp:
```
extern "C" {

int my_cpp_function()
{
  ...
}
}
```

Integration Approaches for External Fortran Code

To integrate external Fortran code:

Write an S-function and corresponding TLC file.
Add the S-function to your model.
If necessary, add support files and control model code generation and builds within the Simulink environment.

See C/C++ S-Function Basics, Integrate Fortran Code into Simulink, S-Functions and Code Generation, and Fortran S-Function Examples.

Insert External Code into Stateflow Charts

Integrate External Code for Library Charts
Integrate External Code for All Charts

Integrate External Code for Library Charts

To integrate external code that applies only to Stateflow library charts for code generation, for each library model that contributes a chart to your main model, complete these steps. Then, generate code.

In the Stateflow Editor, open the Model Configuration Parameters dialog box. Select parameter Use local custom code settings (do not inherit from main model),
The library model retains its own custom code settings during code generation.
Specify your custom code in the subpanes.
Follow the guidelines in Specify Relative Paths to Custom Code (Stateflow).
If you specified custom code settings for simulation, you can apply these settings to code generation. To avoid entering the same information twice, select Use the same custom code settings as Simulation Target.
Click OK.

After completing these steps for each library model, generate code.

Integrate External Code for All Charts

To integrate external code that applies to all charts for code generation:

Specify custom code options for code generation of your main model.
1. In the Model Configuration Parameters dialog box, select Code Generation > Custom Code.
2. In the custom code text fields, specify your custom code.
  Follow the guidelines in Specify Relative Paths to Custom Code (Stateflow).
  If you specified custom code settings for simulation, you can apply these settings to code generation. To avoid entering the same information twice, select Use the same custom code settings as Simulation Target.
Configure code generation for each library model that contributes a chart to your main model. In the Stateflow Editor, open the Model Configuration Parameters dialog box. Clear parameter Use local custom code settings (do not inherit from main model). The library charts inherit the custom code settings of your main model. Click OK.
Generate code.