Real-Time Workshop

Parameter Objects

This section discusses how to use parameter objects in code generation.

Configuring Parameter Objects for Code Generation

In configuring parameter objects for code generation, you use the following code generation and parameter object properties:

• The Inline parameters option (see Parameters: Storage, Interfacing, and Tuning).
• Parameter object properties:
• Value. This property is the numeric value of the object, used as an initial (or inlined) parameter value in generated code.
• RTWInfo.StorageClass. This property controls the generated storage declaration and code for the parameter object.

• Other parameter object properties (such as user-defined properties of classes derived from Simulink.Parameter) do not affect code generation.

Note    If Inline parameters is off (the default), the RTWInfo.StorageClass parameter object property is ignored in code generation.

Effect of Storage Classes on Code Generation for Parameter Objects

Real-Time Workshop generates code and storage declarations based on the RTWInfo.StorageClass property of the parameter object. The logic is as follows:

• If the storage class is 'Auto' (the default), the parameter object is inlined (if possible), using the Value property.
• For storage classes other than 'Auto', the parameter object is handled as a tunable parameter.
• A global storage declaration is generated. You can use the generated storage declaration to make the variable visible to your hand-written code. You can also make variables declared in your hand-written code visible to the generated code.
• The symbolic name of the parameter object is preserved in the generated code.

See Table 5-6 for examples of code generated for each possible setting of RTWInfo.StorageClass.

Example of Parameter Object Code Generation

In this section, we use the Gain block computations of the model shown in the figure below as an example of how Real-Time Workshop generates code for a parameter object.

Figure 5-5: Model Using Parameter Object Kp As Block Parameter

In this model, Kp sets the gain of the Gain1 block.

To configure a parameter object such as Kp for code generation:

1. Define a subclass of Simulink.Parameter. In this example, the parameter object is an instance of the example class SimulinkDemos.Parameter, which is provided with Simulink. For the definition of SimulinkDemos.Parameter, see the directory
   matlabroot/toolbox/simulink/simdemos/@SimulinkDemos.
2. Instantiate a parameter object from your subclass. The following example instantiates Kp as a parameter object of class SimulinkDemos.Parameter.

• Kp = SimulinkDemos.Parameter;
  

1. Make sure that the name of the parameter object matches the desired block parameter in your model. This ensures that Simulink can associate the parameter name with the correct object. For example, in the model of Figure 5-5, the Gain block parameter Kp resolves to the parameter object Kp.

3. Set the object properties.You can do this via the Simulink Data Explorer. Alternatively, you can assign properties via MATLAB commands, as follows:
• Set the Value property, for example:

• Kp.Value = 5.0;

• Set the RTWInfo.StorageClass property, for example:

• Kp.RTWInfo.StorageClass = 'ExportedGlobal';

Table 5-6 shows the variable declarations for Kp and the code generated for the Gain block in the model shown in Figure 5-5, with Inline parameters on. (Due to expression folding optimizations, the gain computation is included in the output computation.) An example is shown for each possible setting of RTWInfo.StorageClass.

Table 5-6: Code Generation from Parameter Objects (Inline Parameters ON)

StorageClass Property	Generated Variable Declaration and Code
Auto	rtY.Out1 = (5.0 * rtb_u)
Simulink Global	typedef struct Parameters_tag { real_T Kp; . . Parameters rtP = { 5.0 }; . . rtY.Out1 = (rtP.Kp * rtb_u);
Exported Global	extern real_T Kp; . . real_T Kp = 5.0; . . rtY.Out1 = (Kp * rtb_u);
Imported Extern	extern real_T Kp; . . rtY.Out1 = (Kp * rtb_u);
Imported Extern Pointer	extern real_T *Kp; . . rtY.Out1 = ((*Kp) * rtb_u);

Simulink Data Objects and Code Generation

Parameter Object Configuration Quick Reference Diagram