Why Generate Code from Simulink Function Blocks and Function Callers?

Simulink Function blocks provide a mechanism for generating C or C++ code for modeling components that represent shared resources. You define the logic as a resource in a Simulink Function block, which separates the function interface (name and arguments) from the implementation of the logic. Function callers (Function Caller blocks, MATLAB Function blocks, and Stateflow^® charts) can then reuse the function logic at different levels of the model hierarchy.

Simulink Function blocks provide an alternative to reusable subsystems. For example, a consideration for using a Simulink Function block instead of a subsystem block is that a Simulink Function block shares states between function callers. The code generator produces one function. If the Simulink Function block contains blocks that have states, such as a delay or memory, the states persist between function callers. The order of the function calls is an important consideration.

Reusable functions that the code generator produces from subsystems do not share states. The code generator produces one function for multiple instances of the subsystem as an optimization. If that subsystem contains blocks that have states, the code generator produces one function, but passes a different state variable to each instance. The instances do not share states.

Other uses of Simulink Function blocks and callers include:

Implementation Options

Choose how to implement Simulink^® functions and function callers based on your code generation requirements. Considerations include:

Choose a Modeling Pattern

This table shows C code for a function that multiplies an input value times two and a Simulink Function block that can represent that function in a Simulink model.

#include "timestwo_sf.h"

#include "ex_slfunc_comp_sf.h"
#include "ex_slfunc_comp_sf_private.h"

void timestwo_sf(real_T rtu_x, real_T *rty_y)
{
  *rty_y = 2.0 * rtu_x;
}

A Simulink function caller invokes a function defined with a Simulink Function block. From anywhere in a model or chart hierarchy, you can call a function defined with a Simulink Function block by using one of these modeling elements:

void ex_slfunc_comp_sf_step(void)
{
  real_T rtb_FunctionCaller1;

timestwo_sf(ex_slfunc_comp_sf_U.In1, &rtb_FunctionCaller1);

ex_slfunc_comp_sf_Y.Out1 = rtb_FunctionCaller1;
.
.
.

void ex_slfunc_comp_gf_step(void)
{
  real_T rtb_y1_l;

  timestwo_gf(ex_slfunc_comp_gf_U.In4, &rtb_y1_l);

  ex_slfunc_comp_gf_Y.Out4 = rtb_y1_l;  
  .
  .
  .

void ex_slfunc_comp_mf_step(void)
{ 
  real_T rtb_y;
  
  timestwo_mf(ex_slfunc_comp_mf_U.In3, &rtb_y);

  ex_slfunc_comp_mf_Y.Out3 = rtb_y;
  .
  .
  .

For more information about modeling choices, see Simulink Functions Overview.

Specify Function Scope

A function that you define with a Simulink Function block can be global or scoped.

For more information, see and Scoped, Global, and Port-Scoped Simulink Function Blocks Overview.

Decide Whether to Generate Export Function Code

Although you can use Simulink Function blocks in a single top-model design, function code is more reusable when you generate it as standalone, atomic components. If you are using Embedded Coder, you can design functions in the context of export-function models.

For information, see Generate Component Source Code for Export to External Code Base (Embedded Coder) and Export-Function Models Overview.

Configure Function Code Interfaces

With Embedded Coder, simplify integration of generated code with external code by configuring generated function code interfaces for Simulink Function and Function Caller blocks. You can configure the function interfaces for:

For more information, see Configure Entry-Point Function Interfaces for Simulink Function and Function Caller Blocks (Embedded Coder).

Uncalled Simulink Function Blocks

If you use a Simulink Function block in a rate-based model and do not call that function, the code generator treats the Simulink Function block as a constant and does not produce function code. For example, this can occur during model development when you are ready to define a function, but are not ready to identify a caller.

To identify such blocks in a rate-based model, display sample time colors during simulation (see View Sample Time Information). By default, Constant blocks appear magenta. Because the code generator considers uncalled Simulink Function blocks constants during simulation, they appear magenta.

Requirements

Limitations

Generate Code for Simulink Function and Function Caller

This example shows how to generate C code for Simulink Function and Function Caller blocks and displays the relevant generated code.

Open the example model SimulinkFunctionsTestHarness. The model uses Stateflow software, but this example reviews only the code generated from the referenced models.

open_system('SimulinkFunctionsTestHarness')

open_system('SimulinkFunctions')

void SimulinkFunctions_initialize(void)
{
  rtDWork.Delay_DSTATE = 1;
}

void f3(real_T rtu_u, real_T *rty_y)
{
  int8_T = rtb_Gain;

  rtY.TicToc10 = rtDWork.Delay_DSTATE;

  rtb_Gain = (int8_T)(int32_T)-(int32_T)rtY.TicToc10;

  adder(rtB.Subtract, rtU.U2, rtu_u, &rtB.FunctionCaller);

  *rty_y = rtB.FunctionCaller;

  rtDWork.Delay_DSTATE = rtb_Gain;
}

static void adder(real_T rtu_u1, real_T rtu_u2, real_T rtu_u3, real_T *rty_y)
{
  *rty_y = (rtu_u1 + rtu_u2) + rtu_u3;
}

#include "rtwtypes.h"

extern void f3(real_T rtu_u, real_T *rty_y);

open_system('SimulinkFunctionCaller')

void f3_caller(void)
{
  rtY.y = f3(rtu_u);
}