Subsystem masking in Simulink

Introduction

Subsystem masking helps you hide complex details inside a block. It makes models simpler and easier to use.

When you want to reuse a group of blocks without showing all details.

When you want to create a custom block with user-friendly controls.

When you want to protect your model's internal design from others.

When you want to simplify a large model by hiding complexity.

When you want to add documentation or instructions inside a block.

Syntax

Simulink

1. Right-click the subsystem block.
2. Select 'Mask' > 'Create Mask...'.
3. In the Mask Editor, add parameters and controls.
4. Use the 'Initialization' tab to write setup code.
5. Click 'OK' to apply the mask.

The mask lets you add input fields, dropdowns, and buttons.

Initialization code runs when the model starts or parameters change.

Examples

This example shows how to add a gain parameter to control inside the mask.

Simulink

Right-click subsystem > Mask > Create Mask...
Add a parameter named 'Gain'
Use this parameter inside the subsystem blocks

This example shows how to add a dropdown to select modes inside the mask.

Simulink

Add a popup menu with options 'Low', 'Medium', 'High'
Use the selected option to change block behavior

Sample Program

This example shows how to mask a subsystem to control the Gain block inside using a mask parameter.

Simulink

1. Create a subsystem with a Gain block named 'Gain' inside.
2. Right-click the subsystem and select 'Mask' > 'Create Mask...'.
3. Add a parameter named 'GainValue' with default 5.
4. In the Initialization tab, write: set_param([gcbh '/Gain'], 'Gain', num2str(GainValue));
5. Click OK.
6. Now, changing 'GainValue' on the mask changes the Gain block inside.

Important Notes

Always test your mask parameters to ensure they update the subsystem correctly.

You can add help text inside the mask to guide users.

Masking does not change the subsystem functionality, only its interface.

Summary

Subsystem masking hides complexity and creates user-friendly blocks.

You can add parameters and controls to customize the subsystem.

Initialization code helps connect mask parameters to internal blocks.

Practice

1. What is the main purpose of masking a subsystem in Simulink?

easy

A. To automatically generate code

B. To hide the internal details and provide a simple interface

C. To increase the simulation speed

D. To change the solver settings

Solution

1. Step 1: Understand what masking does

   Masking a subsystem hides its internal blocks and connections from the user.

2. Step 2: Identify the main benefit

   This makes the subsystem easier to use by showing only relevant parameters and controls.

3. Final Answer:

   To hide the internal details and provide a simple interface -> Option B

4. Quick Check:

   Masking = Hide complexity [OK]

Hint: Masking simplifies subsystems by hiding details [OK]

Common Mistakes:

• Thinking masking speeds up simulation
• Confusing masking with code generation
• Assuming masking changes solver settings

2. Which of the following is the correct way to add a mask parameter in Simulink?

easy

A. Drag parameter block inside subsystem

B. Double-click subsystem > Add block > Parameter

C. Right-click subsystem > Properties > Add parameter

D. Right-click subsystem > Mask > Create Mask > Add parameter

Solution

1. Step 1: Locate mask creation menu

   In Simulink, you right-click the subsystem and select Mask > Create Mask to start masking.

2. Step 2: Add parameters in mask editor

   Inside the mask editor, you can add parameters to customize the subsystem interface.

3. Final Answer:

   Right-click subsystem > Mask > Create Mask > Add parameter -> Option D

4. Quick Check:

   Mask parameters added via Mask Editor [OK]

Hint: Use Mask Editor from right-click menu to add parameters [OK]

Common Mistakes:

• Trying to add parameters by adding blocks inside subsystem
• Using Properties instead of Mask menu
• Double-clicking subsystem does not add mask parameters

3. Given this mask initialization code:

gainValue = str2double(get_param(gcb, 'GainParam'));
set_param([gcb '/Gain'], 'Gain', num2str(gainValue));

What does this code do when the mask parameter GainParam changes?

medium

A. It updates the internal Gain block's Gain parameter to the new value

B. It resets the entire subsystem to default settings

C. It changes the mask parameter name to 'Gain'

D. It causes a syntax error due to missing semicolon

Solution

1. Step 1: Read the initialization code

   The code reads the mask parameter 'GainParam' as a string, converts it to a number, then sets the internal Gain block's 'Gain' parameter.

2. Step 2: Understand the effect on the subsystem

   Changing the mask parameter updates the internal block's gain value accordingly.

3. Final Answer:

   It updates the internal Gain block's Gain parameter to the new value -> Option A

4. Quick Check:

   Mask init code updates internal block parameters [OK]

Hint: Mask init code links mask params to internal blocks [OK]

Common Mistakes:

• Confusing parameter update with subsystem reset
• Thinking parameter name changes
• Assuming syntax error due to semicolon (semicolon is optional in MATLAB)

4. You created a mask with a parameter named Threshold. The initialization code is:

threshold = get_param(gcb, 'Threshold');
set_param([gcb '/Compare'], 'Threshold', threshold);

But the internal Compare block's threshold does not update. What is the likely error?

medium

A. The Compare block does not have a 'Threshold' parameter

B. The internal block parameter name is incorrect; it should be 'RelationalOperator'

C. The initialization code is missing a conversion from string to number

D. The mask parameter name 'Threshold' is misspelled in the code

Solution

1. Step 1: Check internal block parameter names

   The Compare block in Simulink does not have a parameter named 'Threshold'; it uses 'RelationalOperator' and inputs for comparison.

2. Step 2: Identify why setting 'Threshold' fails

   Since 'Threshold' is not a valid parameter, set_param silently fails or has no effect.

3. Final Answer:

   The Compare block does not have a 'Threshold' parameter -> Option A

4. Quick Check:

   Block parameters must match internal block's actual names [OK]

Hint: Verify internal block parameter names before setting [OK]

Common Mistakes:

• Assuming all mask parameters map directly to internal block parameters
• Not checking block documentation for parameter names
• Ignoring type conversions when needed

5. You want to create a masked subsystem that lets users select a filter type ('Lowpass', 'Highpass') and set a cutoff frequency. Which approach correctly connects mask parameters to internal blocks?

hard

A. Create separate subsystems for each filter type without masking

B. Add only numeric mask parameters and manually change internal blocks after simulation

C. Add popup mask parameter for filter type, numeric parameter for cutoff, then in init code set internal blocks' parameters accordingly

D. Use mask initialization code to change the mask parameters dynamically during simulation

Solution

1. Step 1: Design mask parameters for user input

   Use a popup parameter for filter type and a numeric parameter for cutoff frequency to simplify user choices.

2. Step 2: Use initialization code to update internal blocks

   In the mask initialization code, read these parameters and set the internal filter blocks' types and cutoff frequencies accordingly.

3. Final Answer:

   Add popup mask parameter for filter type, numeric parameter for cutoff, then in init code set internal blocks' parameters accordingly -> Option C

4. Quick Check:

   Mask parameters + init code = dynamic internal block setup [OK]

Hint: Use mask parameters plus init code to control internal blocks [OK]

Common Mistakes:

• Not using mask parameters for user input
• Trying to change mask parameters during simulation
• Avoiding masking by creating multiple subsystems