Writing S-Functions

Tunable Parameters

Dialog parameters can be either tunable or nontunable. A tunable parameter is a parameter that a user can change while the simulation is running. Use the macro ssSetSFcnParamTunable in mdlInitializeSizes to specify the tunability of each dialog parameter used by the macro.

Note    Dialog parameters are tunable by default. Nevertheless, it is good programming practice to set the tunability of every parameter, even those that are tunable. If the user enables the simulation diagnostic S-function upgrade needed, Simulink issues the diagnostic whenever it encounters an S-function that fails to specify the tunability of all its parameters.

The mdlCheckParameters method enables you to validate changes to tunable parameters during a simulation run. Simulink invokes the mdlCheckParameters method whenever a user changes the values of parameters during the simulation loop. This method should check the S-function's dialog parameters to ensure that the changes are valid.

Note    The S-function's mdlInitializeSizes routine should also invoke the mdlCheckParameters method to ensure that the initial values of the parameters are valid.

The optional mdlProcessParameters callback method allows an S-function to process changes to tunable parameters. Simulink invokes this method only if valid parameter changes have occurred in the previous time step. A typical use of this method is to perform computations that depend only on the values of parameters and hence need to be computed only when parameter values change. The method can cache the results of the parameter computations in work vectors or, preferably, as run-time parameters (see Run-Time Parameters).

Tuning Parameters in External Mode

When a user tunes parameters during simulation, Simulink invokes the S-function's mdlCheckParameters method to validate the changes and then the S-functions' mdlProcessParameters method to give the S-function a chance to process the parameters in some way. Simulink also invokes these methods when running in external mode, but it passes the unprocessed changes on to the S-function target. Thus, if it is essential that your S-function process parameter changes, you need to create a Target Language Compiler (TLC) file that inlines the S-function, including its parameter processing code, during the code generation process. For information on inlining S-functions, see the Target Language Compiler Reference Guide.

Dialog Parameters

Run-Time Parameters