Verifying output with $finish in Verilog - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to end the simulation after displaying the message.

Verilog

initial begin
  $display("Simulation started");
  [1];
end

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

A$finish

B$stop

C$display

D$monitor

Attempts:

3 left

💡 Hint

Common Mistakes

Using $stop instead of $finish causes the simulation to pause but not end.

The $finish system task ends the simulation cleanly after displaying the message.

2fill in blank

medium

Complete the code to display "Test complete" and then end the simulation.

Verilog

initial begin
  $display("Test complete");
  [1];
end

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

A$stop

B$finish

C$write

D$time

Attempts:

3 left

💡 Hint

Common Mistakes

Using $write or $time instead of $finish does not end the simulation.

After displaying the message, $finish ends the simulation.

3fill in blank

hard

Fix the error in the code to properly end the simulation after printing.

Verilog

initial begin
  $display("Done");
  [1];
end

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

A$finish

B$finish()

C$stop

D$stop()

Attempts:

3 left

💡 Hint

Common Mistakes

Adding parentheses to $finish or $stop causes syntax errors.

In Verilog, $finish is used without parentheses to end the simulation.

4fill in blank

hard

Fill both blanks to display "Test passed" and then end the simulation.

Verilog

initial begin
  [1]("Test passed");
  [2];
end

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

A$display

B$write

C$finish

D$stop

Attempts:

3 left

💡 Hint

Common Mistakes

Using $write instead of $display causes no newline after the message.

Using $stop instead of $finish pauses simulation instead of ending it.

Use $display to print the message and $finish to end the simulation.

5fill in blank

hard

Fill all three blanks to display "All tests done", wait 10 time units, then end the simulation.

Verilog

initial begin
  [1]("All tests done");
  #[2];
  [3];
end

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

A$display

B10

C$finish

D$stop

Attempts:

3 left

💡 Hint

Common Mistakes

Using $stop instead of $finish ends simulation incorrectly.

Forgetting the delay causes immediate finish without wait.

Use $display to print, #10 to wait 10 time units, and $finish to end the simulation.

Practice

1. What does the $finish command do in a Verilog simulation?

easy

A. Pauses the simulation temporarily

B. Stops the simulation immediately

C. Restarts the simulation from the beginning

D. Prints the current simulation time

Solution

1. Step 1: Understand the purpose of $finish

   The $finish command is used to stop the Verilog simulation immediately when called.

2. Step 2: Compare with other simulation commands

   Unlike $stop which pauses the simulation, $finish ends it completely.

3. Final Answer:

   Stops the simulation immediately -> Option B

4. Quick Check:

   $finish = stop simulation [OK]

Hint: Remember: $finish ends simulation, $stop pauses it [OK]

Common Mistakes:

• Confusing $finish with $stop
• Thinking $finish restarts simulation
• Assuming $finish only pauses simulation

2. Which of the following is the correct way to end a Verilog testbench simulation?

easy

A. $finish;

B. end_simulation;

C. finish();

D. $stop;

Solution

1. Step 1: Identify correct syntax for ending simulation

   In Verilog, $finish; is the correct system task to end simulation.

2. Step 2: Check other options for syntax errors

   $stop; pauses simulation, finish(); and end_simulation; are invalid syntax.

3. Final Answer:

   $finish; -> Option A

4. Quick Check:

   Correct syntax to end simulation = $finish; [OK]

Hint: Use $finish; with semicolon to end simulation [OK]

Common Mistakes:

• Using $stop; instead of $finish;
• Writing finish() like a function
• Missing semicolon after $finish

3. What will be the output of this Verilog code snippet?

initial begin
  $display("Start");
  $finish;
  $display("End");
end

medium

A. Start\nEnd

B. End

C. No output

D. Start

Solution

1. Step 1: Trace the code execution order

   The first $display prints "Start". Then $finish stops simulation immediately.

2. Step 2: Understand effect of $finish on following statements

   Because simulation ends at $finish, the second $display is never executed.

3. Final Answer:

   Start -> Option D

4. Quick Check:

   Output before $finish runs = Start [OK]

Hint: Code after $finish; does not run [OK]

Common Mistakes:

• Expecting output after $finish
• Confusing $finish with $stop
• Ignoring simulation stop effect

4. Identify the error in this Verilog testbench snippet:

initial begin
  $display("Test started");
  $finish
  $display("Test ended");
end

medium

A. Cannot use $finish inside initial block

B. Incorrect use of $display

C. Missing semicolon after $finish

D. No error, code is correct

Solution

1. Step 1: Check syntax of system tasks

   System tasks like $finish require a semicolon at the end.

2. Step 2: Identify missing semicolon

   The code misses a semicolon after $finish, causing a syntax error.

3. Final Answer:

   Missing semicolon after $finish -> Option C

4. Quick Check:

   Always end $finish with semicolon [OK]

Hint: Always put semicolon after $finish [OK]

Common Mistakes:

• Omitting semicolon after $finish
• Thinking $finish can't be in initial block
• Misusing $display syntax

5. You want to run multiple tests in a Verilog testbench and stop simulation only after all tests finish. Which is the best way to use $finish?

hard

A. Call $finish at the end of the last test

B. Call $finish immediately after the first test

C. Call $finish inside every test block

D. Never use $finish to stop simulation

Solution

1. Step 1: Understand simulation flow for multiple tests

   Simulation should continue running until all tests complete to verify all outputs.

2. Step 2: Place $finish after last test

   Calling $finish after the last test ends simulation cleanly once all tests are done.

3. Final Answer:

   Call $finish at the end of the last test -> Option A

4. Quick Check:

   $finish after all tests = clean end [OK]

Hint: Use $finish once after all tests complete [OK]

Common Mistakes:

• Stopping simulation too early with $finish
• Calling $finish multiple times unnecessarily
• Avoiding $finish and letting simulation run forever