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Parameterizing Your Driver

You can add a custom icon, dialog box, and initialization commands to an S-Function block by masking it. This provides an easy-to-use graphical user interface for your device driver in the Simulink environment.

You can parameterize your driver by letting the user enter hardware-related variables. Figure 14-7 shows the dialog box of a masked device driver block for an input (ADC) device. The Simulink user can enter the device address, the number of channels, and other operational parameters.

Figure 14-7: Dialog Box for a Masked ADC Driver Block

A masked S-Function block obtains parameter data from its dialog box using macros and functions provided for the purpose.

To obtain a parameter value from the dialog:

1. Access the parameter from the dialog box using the ssGetSFcnParam macro. The arguments to ssGetSFcnParam are a pointer to the block's Simstruct, and the index (0-based) to the desired parameter. For example, use the following call to access the Number of Channels parameter from the dialog above.

• ssGetSFcnParam(S,3); /* S points to block's Simstruct */
  

2. Parameters are stored in arrays of type mxArray, even if there is only a single value. Get a particular value from the input mxArray using the mxGetPr function. The following code fragment extracts the first (and only) element in the Number of Channels parameter.

• #define  NUM_CHANNELS_PARAM         (ssGetSFcnParam(S,3))
  #define NUM_CHANNELS ((uint_T) mxGetPr(NUM_CHANNELS_PARAM)[0])
  uint_T num_channels;
  num_channels = NUM_CHANNELS;
  

It is typical for a device driver block to read and validate input parameters in its mdlInitializeSizes function. See the listing adc.c for an example.

By default, S-function parameters are tunable. To make a parameter nontunable, use the ssSetSFcParamNotTunable macro in the mdlInitializeSizes routine. Nontunable S-function parameters become constants in the generated code, improving performance.

For further information on creation and use of masked blocks, see the Using Simulink and Writing S-Functions manuals.

Device Driver Requirements and Limitations

Writing a Noninlined S-Function Device Driver