Writing S-Functions

Creating Code-Reuse-Compatible S-Functions

The code reuse feature of the Real-Time Workshop generates code for a subsystem in the form of a function that is invoked wherever the subsystem occurs in the model (see Nonvirtual Subsystem Code Generation Options in the online Real-Time Workshop documentation). If a subsystem contains S-functions, the S-functions must be compatible with the code reuse feature. Otherwise, the Real-Time Workshop may not generate reusable code from the subsystem or may generate incorrect code.

If you want your S-function to support the subsystem code reuse feature, you must ensure that the S-function meets the following requirements:

• The S-function must be inlined.
• Code generated from the S-function must not use static variables.
• The TLC code that generates the inlined S-function code must not use the BlockInstanceData function.
• The S-function must initialize its pointer work vector in mdlStart and not before.
• The S-function must not be a sink that logs data to the workspace.
• The S-function must register its parameters as run time parameters in mdlSetWorkWidths. (It must not use ssWriteRTWParameters in its mdlRTW function for this purpose.)

In addition to meeting the preceding requirements, your S-function must set the SS_OPTION_WORKS_WITH_CODE_REUSE flag (see ssSetOptions). This flag assures RTW that your S-function meets the requirements for subsystem code reuse.

The Direct-Index Lookup Table Example

S-Function Callback Methods