Real-Time Workshop User's Guide

Automated S-Function Generation

The Generate S-function feature automates the process of generating an S-function from a subsystem. In addition, the Generate S-function feature presents a display of parameters used within the subsystem, and lets you declare selected parameters tunable.

As an example, consider SourceSubsys, the subsystem illustrated in Figure 10-2. Our objective is to automatically extract SourceSubsys from the model and build an S-Function block from it, as in the previous example. In addition, we want to set the gain factor of the Gain block within SourceSubsys to the workspace variable K (as illustrated below) and declare K as a tunable parameter.

To auto-generate an S-function from SourceSubsys with tunable parameter K:

1. Click on the subsystem to select it.
2. Select Generate S-function from the Real-Time Workshop submenu of the Tools menu. This menu item is enabled when a subsystem is selected in the current model.

   Alternatively, you can choose Generate S-function from the Real-Time Workshop submenu of the subsystem block's context menu.

3. A window displaying a list of the subsystem parameters opens.

In the illustration above, the parameter K is declared tunable.

4. After selecting tunable parameters, click the Build button. This initiates code generation and compilation of the S-function, using the S-function target. The Create New Model option is automatically enabled.
5. The build process displays status messages in the MATLAB command window. When the build completes, the tunable parameters window closes, and a new untitled model window opens.

6. The model window contains an S-Function block, subsys_blk, where subsys is the name of the subsystem from which the block was generated.

The generated S-function component, subsys, is stored in the working directory. The generated source code for the S-function is written to a build directory, subsys_sfcn_rtw.

7. Note that the untitled generated model does not persist, unless you save it via the File menu.
8. Note that the generated S-Function block has inports and outports whose widths and sample times correspond to those of the original model.

The following code fragment, from the mdlOutputs routine of the generated S-function code (in SourceSubsys_sf.c), illustrates how the tunable variable K is referenced via calls to the MEX API.

static void mdlOutputs(SimStruct *S, int_T tid)
...
real_T rtb_temp3[2];
...
/* Gain Block: <S1>/Gain */
rtb_temp3[0] *= ((*(real_T *)(mxGetData(K(S)))));
rtb_temp3[1] *= ((*(real_T *)(mxGetData(K(S)))));

Note    In automatic S-function generation, the Use Value for Tunable Parameters option is always set to its default value (off).

Tunable Parameters in Generated S-Functions

Restrictions