Entry, during, and exit actions in Simulink - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an entry action in a state.

Simulink

state EntryActionState {
    entry: [1];
}

Drag options to blanks, or click blank then click option'

Adisp('Entering state')

Bexit('Leaving state')

Cduring('Running state')

Dwait('Idle')

Attempts:

3 left

💡 Hint

Common Mistakes

Using exit action code in entry action.

Confusing during action with entry action.

The entry action runs when the state is entered. Using disp('Entering state') shows a message at entry.

2fill in blank

medium

Complete the code to define a during action that runs repeatedly in a state.

Simulink

state DuringActionState {
    during: [1];
}

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Adisp('State active')

Bdisp('Exiting state')

Cdisp('Entering state')

Ddisp('Idle')

Attempts:

3 left

💡 Hint

Common Mistakes

Using entry or exit action code in during action.

Not understanding that during runs repeatedly.

The during action runs repeatedly while the state is active. disp('State active') shows a message continuously.

3fill in blank

hard

Fix the error in the exit action code to correctly display a message when leaving the state.

Simulink

state ExitActionState {
    exit: [1];
}

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Adisp('Entering state')

Bdisp('Leaving state')

Cdisp('State active')

Ddisp('Idle')

Attempts:

3 left

💡 Hint

Common Mistakes

Using entry or during messages in exit action.

Not using disp() function.

The exit action runs once when leaving the state. Using disp('Leaving state') correctly shows the exit message.

4fill in blank

hard

Fill both blanks to create a state with entry and exit actions that display messages.

Simulink

state MessageState {
    entry: [1];
    exit: [2];
}

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Adisp('Start')

Bdisp('Stop')

Cdisp('Running')

Ddisp('Idle')

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping entry and exit messages.

Using during action messages in entry or exit.

The entry action uses disp('Start') to show a start message. The exit action uses disp('Stop') to show a stop message.

5fill in blank

hard

Fill all three blanks to create a state with entry, during, and exit actions that display messages.

Simulink

state FullActionState {
    entry: [1];
    during: [2];
    exit: [3];
}

Drag options to blanks, or click blank then click option'

Adisp('Entering')

Bdisp('Active')

Cdisp('Exiting')

Ddisp('Idle')

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up messages between entry, during, and exit.

Forgetting to use disp() in one of the actions.

The entry action shows disp('Entering'), the during action shows disp('Active'), and the exit action shows disp('Exiting'). This covers all three action types.

Practice

1. In Simulink Stateflow, what is the purpose of an entry action in a state?

easy

A. To execute code continuously while the state is active

B. To execute code once when the state is entered

C. To execute code once when the state is exited

D. To define transitions between states

Solution

1. Step 1: Understand what entry action means

   An entry action runs only once when the state becomes active, right at the moment of entry.

2. Step 2: Compare with other actions

   During actions run continuously while in the state, exit actions run once when leaving the state, and transitions define movement between states.

3. Final Answer:

   To execute code once when the state is entered -> Option B

4. Quick Check:

   Entry action = runs once on entering state [OK]

Hint: Entry actions run once at state start, not continuously [OK]

Common Mistakes:

• Confusing entry with during actions
• Thinking entry runs multiple times
• Mixing entry with exit actions

2. Which of the following is the correct syntax to define an exit action in a Simulink Stateflow state named Idle?

easy

A. exit() { disp('Exiting Idle'); }

B. on exit: disp('Exiting Idle');

C. exit: disp('Exiting Idle');

D. exit_action: disp('Exiting Idle');

Solution

1. Step 1: Recall exit action syntax in Stateflow

   Exit actions are defined with the keyword exit: followed by the action code.

2. Step 2: Check each option

   exit: disp('Exiting Idle'); uses correct exit: syntax. on exit: disp('Exiting Idle'); uses incorrect on exit:. exit() { disp('Exiting Idle'); } uses function style which is invalid. exit_action: disp('Exiting Idle'); uses exit_action: which is not recognized.

3. Final Answer:

   exit: disp('Exiting Idle'); -> Option C

4. Quick Check:

   Exit action syntax = exit: code [OK]

Hint: Exit actions start with 'exit:' keyword followed by code [OK]

Common Mistakes:

• Using 'on exit:' instead of 'exit:'
• Trying to define exit as a function
• Using incorrect keywords like 'exit_action:'

3. Consider the following Stateflow state Processing with these actions:

entry: count = 0;
during: count = count + 1;
exit: disp(count);

What will be displayed when the state Processing is exited after being active for 3 simulation steps?

medium

A. 3

B. 1

C. 0

D. 4

Solution

1. Step 1: Track variable changes during state

   On entry, count is set to 0. During each step, it increments by 1. After 3 steps, count = 3.

2. Step 2: Determine exit action output

   On exit, disp(count) prints the current count, which is 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Count increments 3 times, exit prints 3 [OK]

Hint: Count increments during each step, exit prints final count [OK]

Common Mistakes:

• Forgetting entry sets count to 0
• Assuming exit prints 0 or 1
• Counting one extra increment

4. You have this Stateflow state code:

entry: x = 5;
during: x = x + 2;
exit: disp(x);

But when you run the simulation, disp(x) shows 5 instead of increasing values. What is the likely error?

medium

A. The during action is not executing because the state is not active long enough

B. The entry action resets x every step

C. The exit action is placed incorrectly inside the during block

D. The variable x is not declared

Solution

1. Step 1: Analyze why during action might not run

   If the state is active only one step or immediately exited, the during action does not get a chance to increment x.

2. Step 2: Check other options for correctness

   Entry runs once on entry, not every step. Exit action placement is correct. Variable declaration is not required to see this behavior.

3. Final Answer:

   The during action is not executing because the state is not active long enough -> Option A

4. Quick Check:

   During runs only while state active [OK]

Hint: During runs only if state stays active multiple steps [OK]

Common Mistakes:

• Thinking entry runs every step
• Misplacing exit action inside during
• Assuming variable declaration causes issue

5. You want to count how many times a state Active is entered during a simulation. Which approach correctly uses entry, during, and exit actions to achieve this?

hard

A. Use entry: count = 0; to reset count every time state is entered

B. Use during: count = count + 1; to increment count continuously while active

C. Use exit: count = count + 1; to increment count when leaving the state

D. Use entry: count = count + 1; and initialize count outside the state; no during or exit needed

Solution

1. Step 1: Understand counting entries

   To count entries, increment count once each time the state is entered. This is done in the entry action.

2. Step 2: Evaluate other options

   During increments continuously, not suitable for counting entries. Exit increments on leaving, not entering. Resetting count on entry loses previous counts.

3. Final Answer:

   Use entry: count = count + 1; and initialize count outside the state; no during or exit needed -> Option D

4. Quick Check:

   Entry action increments count once per entry [OK]

Hint: Increment count in entry action, initialize count outside [OK]

Common Mistakes:

• Incrementing count in during action
• Resetting count on every entry
• Incrementing count on exit instead of entry