Brake Light Control

September 15, 2025

Solving Approach

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Code

module brake_light (
    input  brake_pedal,
    output reg brake_light
);
    always @(*) begin
        // Write solution here using if statement
        if (brake_pedal) brake_light<=1;
        else brake_light<=0;
    end
endmodule

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Testbench Code

`timescale 1ns/1ps

module tb_brake_light;
    // Input
    reg brake_pedal;

    // DUT output
    wire brake_light;

    // Expected (prefixed expected_)
    wire expected_brake_light;

    // Mismatch signal
    reg mismatch;
    wire mismatch_w = (brake_light !== expected_brake_light);

    // Counters
    integer TOTAL_TEST_CASES        = 0;
    integer TOTAL_PASSED_TEST_CASES = 0;
    integer TOTAL_FAILED_TEST_CASES = 0;

    // VCD control
    integer VCD_MAX_CASES = 32;

    // DUT
    brake_light dut(.brake_pedal(brake_pedal), .brake_light(brake_light));

    // Golden model (no latch, pure comb)
    assign expected_brake_light = (brake_pedal) ? 1'b1 : 1'b0;

    // VCD dump (ordered: Inputs → Outputs → Expected → Mismatch)
    initial begin
        $dumpfile("tb_brake_light.vcd");
        $dumpvars(0,
            tb_brake_light.brake_pedal,         // Input
            tb_brake_light.brake_light,         // DUT output
            tb_brake_light.expected_brake_light,// Expected
            tb_brake_light.mismatch             // Mismatch
        );
        $dumpon; // start at time 0
    end

    // Init and header
    initial begin
        brake_pedal = 1'b0;
        mismatch = 1'b0;
        $display("brake_pedal | DUT_brake_light | expected_brake_light | mismatch");
        $display("---------------------------------------------------------------");
    end

    // Apply + check task
    task apply_and_check;
        input t_pedal;
        begin
            brake_pedal = t_pedal;
            #1; // settle

            mismatch = mismatch_w;

            TOTAL_TEST_CASES++;
            if (!mismatch) TOTAL_PASSED_TEST_CASES++;
            else           TOTAL_FAILED_TEST_CASES++;

            $display("     %b      |        %b         |          %b          |    %0d",
                brake_pedal, brake_light, expected_brake_light, mismatch);

            if (TOTAL_TEST_CASES == VCD_MAX_CASES) $dumpoff;
        end
    endtask

    // Stimulus (full truth table)
    initial begin
        apply_and_check(1'b0);
        apply_and_check(1'b1);

        // Summary
        $display("---------------------------------------------------------------");
        $display("TOTAL_TEST_CASES=%0d", TOTAL_TEST_CASES);
        $display("TOTAL_PASSED_TEST_CASES=%0d", TOTAL_PASSED_TEST_CASES);
        $display("TOTAL_FAILED_TEST_CASES=%0d", TOTAL_FAILED_TEST_CASES);
        $display("ALL_TEST_CASES_PASSED=%s", (TOTAL_FAILED_TEST_CASES==0) ? "true":"false");

        #2 $finish;
    end
endmodule