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Writing S-Functions That Specify Sample Time Inheritance Rules

For the Simulink engine to accurately determine whether a model can inherit a sample time, the S-functions in the model need to specify how they use sample times. You can specify this information by calling the macro ssSetModelReferenceSampleTimeInheritanceRule from mdlInitializeSizes or mdlSetWorkWidths. To use this macro:

1. Check whether the S-function calls any of the following macros:

   • ssGetSampleTime

   • ssGetInputPortSampleTime

   • ssGetOutputPortSampleTime

   • ssGetInputPortOffsetTime

   • ssGetOutputPortOffsetTime

   • ssGetSampleTimePtr

   • ssGetInputPortSampleTimeIndex

   • ssGetOutputPortSampleTimeIndex

   • ssGetSampleTimeTaskID

   • ssGetSampleTimeTaskIDPtr

2. Check for the following in your S-function TLC code:

   • LibBlockSampleTime

   • CompiledModel.SampleTime

   • LibBlockInputSignalSampleTime

   • LibBlockInputSignalOffsetTime

   • LibBlockOutputSignalSampleTime

   • LibBlockOutputSignalOffsetTime

3. Depending on your search results, use ssSetModelReferenceSampleTimeInheritanceRule as indicated in the following table.

   If...	Use...
   None of the macros or functions are present, the S-function does not preclude the model from inheriting a sample time.	ssSetModelReferenceSampleTimeInheritanceRule (S, USE_DEFAULT_FOR_DISCRETE_INHERITANCE)
   Any of the macros or functions are used for Throwing errors if sample time is inherited, continuous, or constant Checking ssIsSampleHit Checking whether sample time is inherited in either mdlSetInputPortSampleTime or mdlSetOutputPortSampleTime before setting	ssSetModelReferenceSampleTimeInheritanceRule... (S,USE_DEFAULT_FOR_DISCRETE_INHERITANCE)
   The S-function uses its sample time for computing parameters, outputs, and so on	ssSetModelReferenceSampleTimeInheritanceRule (S, DISALLOW_SAMPLE_TIME_INHERITANCE)

Note   If an S-function does not set the ssSetModelReferenceSampleTimeInheritanceRule macro, by default the Simulink engine assumes that the S-function does not preclude the model containing that S-function from inheriting a sample time. However, the engine issues a warning indicating that the model includes S-functions for which this macro is not set.

You can use settings on the Diagnostics/Solver pane of the Configuration Parameters dialog box or Model Explorer to control how the Simulink engine responds when it encounters S-functions that have unspecified sample time inheritance rules. Toggle the Unspecified inheritability of sample time diagnostic to none, warning, or error. The default is warning.

Writing S-Functions That Specify Port Scope and Reusability

Writing S-Functions That Support Code Reuse

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