Target Language Compiler

Inlining M-File S-Functions

All of 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 that while you can fully inline an M-file S-function to achieve top performance--even with Simulink Accelerator--the MATLAB Math Library is not included with Real-Time Workshop, so any high-level MATLAB commands and functions you use in the M-file S-function must be written by hand in the block target file.

A quick example will illustrate the equivalence of C MEX and M-file S-functions for code generation. The M-file S-function timestwo.m is equivalent to the C MEX S-function timestwo. In fact, the TLC file for the C MEX S-function timestwo will work for the M-file S-function timestwo.m as well! Since TLC only requires 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 what the TLC file will be used for

• %implements "timestwo" "C"
  

To try this out for 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, cd to the temporary directory and make a Simulink model with an S-function block that calls timestwo. Since the MATLAB search path will find timestwo.m in the current directory before finding the C MEX S-function timestwo in the matlabpath, Simulink will use 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. Here is the sample model.

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 was

• %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 it show up in the generated code, then work up to algorithmic changes.

A Complete Example

Inlining Fortran (F-MEX) S-Functions