Technical data

Writing Target Language Files

3-32

In general, inlining an S-function is especially useful when:

• The time required to execute the contents of the S-function is small in

comparison to the overhead required to call the S-function.

• Certain S-function routines are empty (e.g.,

mdlUpdate).

• The behavior of the S-function changes between simulation and code

generation. For example, device driver I/O S-functions may read from the

MATLAB workspace during simulation, but read from an actual hardware

address in the generated code.

An Example

Suppose you have a simple S-function that mimics the Gain block with one

input, one output, and a scalar gain. That is,

y = u * p. If the Simulink block’s

name is

foo and the name of the S-function is foogain, the C-coded MEX-file

must contain:

#define S_FUNCTION_NAME foogain

#include "simstruc.h"

#define GAIN mxGetPr(ssGetArg(S,0))[0]

static void mdlInitializeSizes(SimStruct *S)

{

ssSetNumContStates (S, 0);

ssSetNumDiscStates (S, 0);

ssSetNumInputs (S, 1);

ssSetNumOutputs (S, 1);

ssSetNumInputArgs (S, 1);

ssSetDirectFeedThrough (S, 1);

ssSetNumSampleTimes (S, 0);

ssSetNumIWork (S, 0);

ssSetNumRWork (S, 0);

ssSetNumPWork (S, 0);

}

static void

mdlOutputs(real_T *y, const real_T *x, const real_T *u,

SimStruct *S, int_T tid)