Defining a Function That Uses Simulink Blocks

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Goal of the Tutorial Editing a Model to Use a Simulink Function Running the New Model

Goal of the Tutorial

The goal of this tutorial is to use a Simulink function in a Stateflow chart to improve the design of a model named old_sf_car.

Rationale for Improving the Model Design

The old_sf_car model contains a function-call subsystem named Threshold Calculation and a Stateflow chart named shift_logic. The two blocks interact as follows:

• The chart broadcasts the output event CALC_TH to trigger the function-call subsystem.

• The subsystem uses lookup tables to interpolate two values for the shift_logic chart.

• The subsystem outputs (up_th and down_th) feed directly into the chart as inputs.

  No other blocks in the model access the subsystem outputs.

You can replace a function-call subsystem with a Simulink function in a chart when:

• The subsystem performs calculations required by the chart.

• Other blocks in the model do not need access to the subsystem outputs.

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Editing a Model to Use a Simulink Function

The sections that follow describe how to replace a function-call subsystem in a Simulink model with a Simulink function in a Stateflow chart. This procedure reduces the number of objects in the model while retaining the same simulation results.

Step	Task	Reference
1	Open the model.	Open the Model
2	Move the contents of the function-call subsystem into a Simulink function in the chart.	Add a Simulink Function to the Chart
3	Change the scope of specific chart-level data to Local.	Change the Scope of Chart Data
4	Replace the event broadcast with a function call.	Update State Action in the Chart
5	Verify that function inputs and outputs are defined.	Add Data to the Chart
6	Remove unused items in the model.	Remove Unused Items in the Model

Note   To skip the conversion steps and access the new model directly, type sf_car at the MATLAB command prompt.

Open the Model

Type old_sf_car at the MATLAB command prompt. If you simulate the model, you see these results in the two scopes.

Add a Simulink Function to the Chart

Follow these steps to add a Simulink function to the shift_logic chart.

1. In the Simulink model, right-click the Threshold Calculation block in the lower left corner and select Cut from the context menu.

   

2. Open the shift_logic chart.

3. In the chart, right-click below selection_state and select Paste from the context menu.

4. Expand the new Simulink function so that the signature fits inside the function box.

   

   Tip   To change the font size of a function, right-click the function box and select a new size from the Font Size menu.

5. Expand the border of selection_state to include the new function.

   

   Note   The function resides in this state instead of the chart level because no other state in the chart requires the function outputs up_th and down_th. See How a Simulink Function Binds to a State.

6. Rename the Simulink function from Threshold_Calculation to calc_threshold by entering [down_th, up_th] = calc_threshold(gear, throttle) in the function box.

Change the Scope of Chart Data

In the Model Explorer, change the scope of chart-level data up_th and down_th to Local because calculations for those data now occur inside the chart.

Update State Action in the Chart

In the Stateflow Editor, change the during action in selection_state to call the Simulink function calc_threshold.

during: [down_th, up_th] = calc_threshold(gear, throttle);

Add Data to the Chart

Because the function calc_threshold takes throttle as an input, you must define that data as a chart input. (For details, see Adding Data.)

1. Add input data throttle to the chart with a Port property of 1.

   Using port 1 prevents signal lines from overlapping in the Simulink model.

2. In the Simulink model, add a signal line for throttle between the inport of the Engine block and the inport of the shift_logic chart.

Remove Unused Items in the Model

1. In the Model Explorer, delete the function-call output event CALC_TH because the Threshold Calculation block no longer exists.

2. Delete any dashed signal lines from your model.

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Running the New Model

Your new model looks something like this:

If you simulate the new model, the results match those of the original design.

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Best Practices for Using Simulink Functions

Scheduling Execution of Multiple Controllers

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