Elevator Indicator

March 29, 2026

Solving Approach

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Code

module elevator_floor16 (
    input  [3:0] floor,
    output [15:0] leds
);

wire [15:0] stage0, stage1, stage2, stage3, stage4;

// input ban đầu = 1
assign stage0 = 16'b0000_0000_0000_0001;

// tầng 1: shift 1 (b0)
assign stage1 = floor[0] ? (stage0 << 1) : stage0;

// tầng 2: shift 2 (b1)
assign stage2 = floor[1] ? (stage1 << 2) : stage1;

// tầng 3: shift 4 (b2)
assign stage3 = floor[2] ? (stage2 << 4) : stage2;

// tầng 4: shift 8 (b3)
assign stage4 = floor[3] ? (stage3 << 8) : stage3;

// output
assign leds = stage4;

endmodule

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Testbench Code

`timescale 1ns/1ps

module tb_elevator_floor16;
    // Input
    reg  [3:0]  floor;

    // DUT output
    wire [15:0] leds;

    // Expected
    reg  [15:0] expected_leds;

    // Mismatch flag (high when DUT != expected)
    wire mismatch = (leds !== expected_leds);

    integer TOTAL_TEST_CASES        = 0;
    integer TOTAL_PASSED_TEST_CASES = 0;
    integer TOTAL_FAILED_TEST_CASES = 0;

    // Instantiate DUT
    elevator_floor16 dut (
        .floor(floor),
        .leds(leds)
    );

    // VCD dump (Inputs -> Outputs -> Expected -> mismatch)
    initial begin
        $dumpfile("tb_elevator_floor16.vcd");
        $dumpvars(0,
            tb_elevator_floor16.floor,        // input
            tb_elevator_floor16.leds,         // output
            tb_elevator_floor16.expected_leds,// expected
            tb_elevator_floor16.mismatch      // mismatch
        );
    end

    // Golden model: pure one-hot via shift
    task compute_expected;
        input [3:0] t_floor;
        begin
            expected_leds = (16'b0000_0000_0000_0001 << t_floor);
        end
    endtask

    // Apply, check, print ONE row (no duplicates)
    task run_and_show;
        input [3:0] t_floor;
        begin
            floor = t_floor;
            compute_expected(t_floor);
            #1; // settle

            TOTAL_TEST_CASES = TOTAL_TEST_CASES + 1;
            if (!mismatch) TOTAL_PASSED_TEST_CASES = TOTAL_PASSED_TEST_CASES + 1;
            else           TOTAL_FAILED_TEST_CASES = TOTAL_FAILED_TEST_CASES + 1;

            $display("%2d    | %016b | %016b | %b",
                     floor, leds, expected_leds, mismatch);
        end
    endtask

    integer i;
    initial begin
        // Header
        $display("floor |        leds(15..0)        |     expected_leds     | mismatch");
        $display("----------------------------------------------------------------------");

        // Single exhaustive loop: runs and prints each case exactly once
        for (i = 0; i < 16; i = i + 1)
            run_and_show(i[3:0]);

        // 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");
        $display("======================================");
        $finish;
    end
endmodule