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Inlining M-File S-Functions

All the functionality of M-file S-functions can be inlined in the generated code. Writing a block target file for an M-file S-function is essentially identical to the process for a C MEX S-function.

Note   While you can fully inline an M-file S-function to achieve top performance, a C or C++ API for the MATLAB Math Library is not included with Simulink Accelerator or the Real-Time Workshop software. You therefore cannot call MATLAB Math Library functions from a TLC file.

The following example illustrates the equivalence of C MEX and M-file S-functions for code generation. The S-function M-file timestwo.m is equivalent to the C MEX S-function timestwo. In fact, the TLC file for the C MEX S-function timestwo works for the S-function M-file timestwo.m as well. Because TLC requires only the root name of the S-function and not its type, it is independent of the type of S-function. In the case of timestwo, one line determines how the TLC file will be used:

%implements "timestwo" "C"

To try this yourself, copy file timestwo.m from matlabroot/toolbox/simulink/blocks/ to a temporary directory, then copy the file timestwo.tlc from matlabroot/toolbox/simulink/blocks/tlc_c/ to the same temporary directory. In MATLAB, change directory (cd) to the temporary directory and make a Simulink model with an S-function block that calls timestwo. Here is the sample model:

Because the MATLAB search path will find timestwo.m in the current directory before finding the C MEX S-function timestwo in the matlabpath, Simulink uses the M-file S-function for simulation. Verify which S-function will be used by typing the MATLAB command

which timestwo

The answer you see will be the M-file S-function timestwo.m in the temporary directory.

Upon generating code, you will find that the timestwo.tlc file was used to inline the M-file S-function with code that looks like this (with an input signal width of 5 in this example):

/* S-Function Block: <Root>/m-file S-Function */
  /* Multiply input by two */
  {
    int_T i1;
    const real_T *u0 = &rtB.Gain[0];
    real_T *y0 = &rtB.m_file_S_Function[0];

    for (i1=0; i1 < 5; i1++) {
      y0[i1] = u0[i1] * 2.0;
    }
  }

As expected, each of the inputs, u0[i1], is multiplied by 2.0 to form the output value. The Outputs method in the block target file used to generate this code is

%function Outputs(block, system) Output
/* %<Type> Block: %<Name> */
  %%
  /* Multiply input by two */
  %assign rollVars = ["U", "Y"]
  %roll idx = RollRegions, lcv = RollThreshold, block, "Roller", rollVars
    %<LibBlockOutputSignal(0, "", lcv, idx)> = \
    %<LibBlockInputSignal(0, "", lcv, idx)> * 2.0;
  %endroll
%endfunction

Alter these temporary copies of the M-file S-function and the TLC file to see how they interact. Start out by just changing the comments in the TLC file and see the changes appear in the generated code, then work up to algorithmic changes.

Inlining C MEX S-Functions

Inlining Fortran (F-MEX) S-Functions

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