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Design Charts with Simulink Functions

In this tutorial, you use a Simulink® function in a Stateflow® chart to improve the design of a model that contains a function-call subsystem. 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.

Simulink functions are not supported in standalone Stateflow charts in MATLAB®. For more information, see Reuse Simulink Functions in Stateflow Charts.


To skip the conversion steps, you can open the modified model by entering:


Open the Model

Open the model old_sf_car. This model contains a function-call subsystem named Threshold Calculation and a Stateflow chart named shift_logic.

When you run this model, the chart broadcasts the output event CALC_TH to trigger the function-call subsystem. The subsystem interpolates two values for the shift_logic chart. The subsystem outputs (up_th and down_th) return to the chart as inputs.

After the simulation, the engine RPM Scope block displays these results.

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.

    Simulink model after Threshold Calculation subsystem is removed.

  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.

    Stateflow chart after Simulink function is added.


    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.

    Stateflow chart with a Simulink function inside a state.


    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 Bind a Simulink Function 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);

Stateflow chart with modified during action in state selection_state.

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 Add Stateflow 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 to an input to the Engine block and to an input to 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.

Run the New Model

Your new model looks something like this:

Modified Simulink model without function-call subsystems.

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

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