Timers in Verilog

module timers;
  reg clk;
  integer counter1, counter2;
  reg timer1_fired, timer2_fired, timer2_stopped;

  initial begin
    clk = 0;
    counter1 = 0;
    counter2 = 0;
    timer1_fired = 0;
    timer2_fired = 0;
    timer2_stopped = 0;

    // Simulate a timer that will fire after 2 seconds
    #2000;
    timer1_fired = 1;
    $display("Timer 1 fired");

    // Simulate a timer that we'll stop before it fires
    fork
      begin
        #1000;
        if (!timer2_stopped) begin
          timer2_fired = 1;
          $display("Timer 2 fired");
        end
      end
    join_none

    // Stop timer2 immediately
    timer2_stopped = 1;
    $display("Timer 2 stopped");

    // Wait for 2 seconds to ensure timer2 doesn't fire
    #2000;

    $finish;
  end

  // Clock generation
  always #5 clk = ~clk;

endmodule

In Verilog, we don’t have built-in timer features like in some high-level programming languages. Instead, we simulate the passage of time using delays and clock cycles. Here’s how the code works:

1. We define a module called timers that contains our simulation logic.

2. We create registers to represent the state of our timers and a clock signal.

3. In the initial block, we set up our initial state and simulate our timers:

   • For the first timer, we use a delay of 2000 time units (which we consider equivalent to 2 seconds) before setting timer1_fired and displaying a message.

   • For the second timer, we use a fork-join_none block to start a process that would fire after 1 second. However, we immediately stop this timer by setting timer2_stopped.

4. We use $display to output messages, which is similar to fmt.Println in the original code.

5. We wait for an additional 2 seconds (2000 time units) at the end to ensure the second timer doesn’t fire.

6. Finally, we use $finish to end the simulation.

7. We also include a clock generation block, which toggles the clk signal every 5 time units. This isn’t directly used in this example but is often necessary in more complex Verilog simulations.

To run this Verilog simulation, you would typically use a Verilog simulator like Icarus Verilog or ModelSim. The exact commands may vary depending on your setup, but it might look something like this:

$ iverilog -o timers_sim timers.v
$ ./timers_sim
Timer 2 stopped
Timer 1 fired

This simulation demonstrates the concept of timers in Verilog, although the implementation is quite different from the high-level approach used in the original code. In Verilog, we’re working at a much lower level, simulating the passage of time rather than using operating system-provided timer facilities.