Repeat Loop

Part of the Fundamentals section of Coddy's Verilog journey — lesson 60 of 90.

The repeat loop executes a block of code a fixed number of times. Unlike the for loop, it does not use a loop counter variable.

A repeat loop runs a specified number of times. You give it a constant or expression that determines how many iterations to execute.

Syntax:

repeat (number) begin
  // Code to repeat
end

Simple Example

repeat (5) begin
  $display("Hello");
end

Output:

Hello
Hello
Hello
Hello
Hello

The message prints exactly 5 times.

Repeat with an Expression

integer count = 3;

repeat (count) begin
  $display("Looping");
end

Output:

Looping
Looping
Looping

Repeat vs For Loop

	For Loop	Repeat Loop
Counter variable	Yes (explicit)	No
When to use	Need index value	Just need repetition
Example	`for (i=0; i<5; i=i+1)`	`repeat (5)`

Generating Multiple Clock Cycles

initial begin
  clk = 0;
  repeat (20) begin
    #5 clk = ~clk;
  end
end

This generates 20 clock edges (10 complete cycles).

Important Rules

Rule	Explanation
Number must be non-negative	Cannot repeat negative times
Can use constant or expression	`repeat (10)` or `repeat (count)`
No loop variable available	Cannot track iteration number
Use `begin`/`end` for multiple statements	Required for more than one line

Challenge

What to do:

Add the missing repeat loop to print "Verilog" 4 times.

Cheat sheet

The repeat loop executes a block of code a fixed number of times without a loop counter variable.

repeat (number) begin
  // Code to repeat
end

Can use a constant or variable expression:

integer count = 3;
repeat (count) begin
  $display("Looping");
end

Common use case — generating clock cycles:

repeat (20) begin
  #5 clk = ~clk;
end

Repeat vs For Loop: Use repeat when you only need repetition (no index needed); use for when you need the iteration counter value.

Try it yourself

module repeat_challenge;
  
  initial begin
    $display("Printing 4 times:");
    
    // TODO: Add repeat loop
    // Repeat 4 times
    // Inside, print "Verilog"
    
    $finish;
  end
endmodule