Configure Generated C Function Interface for Model Entry-Point Functions

What Is an Entry-Point Function?

An entry point is a location in code where a transfer of program control (execution) occurs. The main function (main()) is the entry point to a C/C++ program and is called when the application starts executing. Calls to other functions, for example from the main function, provide entry points to function code. Program control is transferred to the called function. The function code executes, and when finished, returns control to the main or other calling function.

When producing code for a model, the code generator defines a set of entry-point functions that you can call to execute the generated code. You can call the generated functions from external code or from a version of the generated main function that you modify.

The Code Interface Report section of the code generation report lists the entry-point functions that the code generator produces for a model. For more information, see Analyze Generated Data Code Interface Report (Embedded Coder).

Types of Generated Entry-Point Functions

The code generator produces entry-point functions for these types of model functions.

Type of Model Function	Model Source Name	Default Generated Function Name	Description
Exported function (requires Embedded Coder^®)	`ExportedFunction:slIdentifier`, where `slIdentifier` is the name of the function-call Inport block in the model	`function-call-inport-block-name` or `signal-label` (if specified)	For an exported-function model, the exported function for a subsystem.
Initialize function	`Initialize`	`model_initialize`	Initialization code for a model. At the start of the application code, call the function once. Do not use this function to reset the real-time model data structure (`rtM`).
Partition function	`Partition:slIdentifier`, where `slIdentifier` is a partition that was created explicitly from a block in the model and shown in the Simulink® Schedule Editor (for example, P1), or a task name in the Concurrent Execution dialog	`model_stepn`, where `n` uniquely identifies the function generated for one of the model sample periods	For a model partition, output and update code. Model configuration parameter Single output/update function is selected (the default).
Partition update function	`PartitionUpdate:slIdentifier`, where `slIdentifier` is a partition that was created explicitly from a block in the model and shown in the Simulink® Schedule Editor (for example, P1), or a task name in the Concurrent Execution dialog	`model_outputn` and `model_updaten`, where `n` uniquely identifies the function generated for one of the model sample periods	For a model partition, output and update code in separate functions. Model configuration parameter Single output/update function is cleared.
Periodic multitasking function	`Periodic:slIdentifier,` where `slIdentifier` is an annotation that corresponds to the sample time period for a periodic or continuous rate of a multitasking model (for example, D1)	`model_stepn`, where `n` uniquely identifies the function generated for one of the model sample periods	For blocks in a rate-based model configured for multitasking, output and update code. The code generator produces a function for each sample period. Model configuration parameter Single output/update function is selected (the default).
Periodic multitasking update function	`PeriodicUpdate:slIdentifier,` where `slIdentifier` is an annotation that corresponds to the sample time period for a periodic or continuous rate of a multitasking model (for example, D1)	`model_outputn` and `model_updaten`, where `n` uniquely identifies the function generated for one of the model sample periods	For blocks in a rate-based model configured for multitasking, output and update code in separate functions. The code generator produces output and update functions for each sample period. Model configuration parameter Single output/update function is cleared.
Periodic single-tasking function	`Periodic`	`model_step`	For blocks in a rate-based model configured for single-tasking, output and update code. Model configuration parameter Single output/update function is selected (the default).
Periodic single-tasking update function	`PeriodicUpdate`	`model_output` and `model_update`	For blocks in a rate-based model configured for single-tasking, output and update code in separate functions. Model configuration parameter Single output/update function is cleared.
Reset function	`Reset:slIdentifier,` where `slIdentifier` is the name of the reset function in the model	`model_reset-function-name`	If the model includes a Reset Function block, reset code generated. To reset conditions or state, call the function from the application code.
Simulink Function	`Simulink Function:slIdentifier,` where `slIdentifier` is the name of the Simulink Function block in the model	`function-name` for a global Simulink Function block or `model_function-name` for a scoped Simulink Function block	For an exported-function model, the exported function for a Simulink Function block.
Terminate function	`Terminate`	`model_terminate`	Code for turning off a system. For ERT-based models, you can suppress generation of this function by clearing the model configuration parameter Terminate function required (Embedded Coder) (set by default).

If you have Embedded Coder software, to facilitate integration of external and generated code and achieve compliance with code standards and guidelines, you can configure how the code generator produces function interfaces from a model or subsystem.

Configure Whether Entry-Point Functions Are Reusable

By default, for top models, the code generator produces code that is not reusable or reentrant. Entry-point functions have a void-void interface. Code communicates with other code by directly accessing global data structures that reside in shared memory.

If your application requires reusable, multi-instance entry-point function code, you can configure the code generator to call each function (instance) with unique data. In this case, the code is reentrant.

You configure whether entry-point functions are reusable with the model configuration parameter Code interface packaging and related parameters. The parameter settings that you choose depend on factors such as configuration selections for the system target file, programming language, and argument interface.

Default Configurations for Single-Instance C Entry-Point Functions

By default, for GRT- and ERT-based system target files, the code generator produces single-instance C entry-point functions. The generated code:

Creates an execution function without arguments (void-void).
Allocates memory statically (at compile time) for model data structures.

The default model configuration parameter settings for configuring single-instance entry-point function code are:

Language set to C.
Code interface packaging set to Nonreusable function.

Generate Reusable, Multi-Instance C Entry-Point Functions

You can configure the code generator to produce reusable entry-point functions in C for either a GRT- or ERT-based system target file. However, the function interfaces that the code generator produces by default varies. Assuming that model configuration parameter Language is set to C and Code interface packaging is set to Reusable function, the code generator produces this entry-point function code for each system target file scenario.

System Target File	Interface
GRT-based	Reusable, multi-instance C entry-point functions that are reentrant. Packs values of model root-level Inport blocks and Outport blocks into the real-time model data structure. Passes that structure to the execution function as an argument by reference. Allocates memory dynamically at runtime for the data of a model instance. Allocates the memory by calling a function, such as `malloc`.
ERT-based	Reusable, multi-instance C entry-point functions that are reentrant. Passes the value of each model root-level Inport block and Outport block to the execution function as a separate argument. Allocates memory statically for model data structures.

If you are using an ERT-based system target file and want to generate reusable, multi-instance C entry-point functions that are reentrant, consider:

Using dynamic memory allocation to initialize model data structures. Select Use dynamic memory allocation for model initialization (Embedded Coder).
Packing values of model root-level Inport blocks into a structure, packing values of root-level Outport blocks into a second structure, and passing the structures to the execution function as arguments by reference. Set Pass root-level I/O as (Embedded Coder) to Structure reference.
Packing values of model root-level Inport blocks and Outport blocks into the real-time model data structure and passing that structure to the execution function as an argument by reference. Set Pass root-level I/O as (Embedded Coder) to Part of model data structure.

How to Interface with Generated Entry-Point Functions

After generating code for a model, use the Code view to review the generated entry-point functions and, if applicable, variables representing external input and output ports.
Add #include statements to your external code that include the generated header files that declare the model entry-point functions.
Add an #include statement that includes the generated file rtwtypes.h. This file provides type definitions, #define statements, and enumerations.
Initialize target-specific data structures and hardware, such as ADCs or DACs.
If applicable, initialize data for each instance of a reusable model.
If applicable, write input data to generated variables that represent model Inport blocks.
Call the generated entry-point functions or set up use of the rt_OneStep function.
If applicable, read data from generated variables that represent model Outport blocks.

For more information, see Deploy Applications to Target Hardware (Embedded Coder).

C Function Interface Customization Limitations

These limitations apply to customizations for generated C function interfaces:

You must select the model configuration parameter Single output/update function.
Multirate models are supported, but you must configure the models for single tasking.
You must configure root-level inports and outports to use the Default storage class.
If you choose to customize a function interface, you must provide your own custom main program. You cannot configure the function interface with the static rt_main.c that MathWorks^® provides. Specifying a function interface configuration other than the default creates a mismatch between the generated code and the default static rt_main.c.
The code generator removes the data structure for the root inports of the model unless a subsystem implemented by a nonreusable function uses the value of one or more of the inports.
The code generator removes the data structure for the root outports of the model except when you enable MAT-file logging or if the sample time of one or more of the outports is not the fundamental base rate (including a constant rate).
If you copy a subsystem block to create a block in a new model or the same model, the function interface information from the original subsystem block is not copied to the new subsystem block.
If you have Stateflow^®, for a Stateflow chart that uses a model root inport value or that calls a subsystem that uses a model root inport value, do one of the following to generate code:
- Clear the Execute (enter) Chart At Initialization check box in the Stateflow chart.
- Make the Stateflow function a nonreusable function.
- Insert a Simulink^® Signal Conversion block immediately after the root inport. In the Signal Conversion block parameters dialog box, select Exclude this block from 'Block reduction' optimization.
If a model root inport value connects to a Simscape™ conversion block, insert a Simulink Signal Conversion block between the root inport and the Simscape conversion block. In the Signal Conversion block parameters dialog box, select Exclude this block from 'Block reduction' optimization.
When building a referenced model that is configured with a function interface, do not use virtual buses as inputs or outputs to the referenced model. Use nonvirtual buses instead.
If the C function interface is not the default, the value is ignored for the model configuration parameter Pass fixed-size scalar root inputs by value for code generation. For more information, see Pass fixed-size scalar root inputs by value for code generation.