Business-code/sim/pwm_control_demo_tb.v

`timescale 1ns/1ps

module pwm_control_demo_tb;

    reg clk;
    reg reset_n;
    reg signed [7:0] cmd;
    reg enable;
    reg fault;

    wire signed [7:0] limited_cmd;
    wire direction;
    wire [6:0] duty;
    wire pwm_out;

    integer errors;
    integer high_count;
    integer i;

    pwm_control_demo dut (
        .clk(clk),
        .reset_n(reset_n),
        .cmd(cmd),
        .enable(enable),
        .fault(fault),
        .limited_cmd(limited_cmd),
        .direction(direction),
        .duty(duty),
        .pwm_out(pwm_out)
    );

    // 100 MHz simulation clock.
    // Frequency itself is not important for this demo;
    // PWM duty ratio is what we verify.
    initial clk = 0;
    always #5 clk = ~clk;

    task check_control;
        input signed [7:0] test_cmd;
        input signed [7:0] expected_limit;
        input expected_direction;
        input [6:0] expected_duty;
        begin
            cmd = test_cmd;
            #1;

            if (limited_cmd !== expected_limit) begin
                $display("FAIL limiter: cmd=%0d expected=%0d actual=%0d",
                         test_cmd, expected_limit, limited_cmd);
                errors = errors + 1;
            end else begin
                $display("PASS limiter: cmd=%0d -> %0d",
                         test_cmd, limited_cmd);
            end

            if (direction !== expected_direction) begin
                $display("FAIL direction: cmd=%0d expected=%0d actual=%0d",
                         test_cmd, expected_direction, direction);
                errors = errors + 1;
            end else begin
                $display("PASS direction: cmd=%0d direction=%0d",
                         test_cmd, direction);
            end

            if (duty !== expected_duty) begin
                $display("FAIL duty: cmd=%0d expected=%0d actual=%0d",
                         test_cmd, expected_duty, duty);
                errors = errors + 1;
            end else begin
                $display("PASS duty: cmd=%0d duty=%0d%%",
                         test_cmd, duty);
            end
        end
    endtask

    task check_pwm;
        input [6:0] expected_percent;
        begin
            high_count = 0;

            // Measure exactly one complete 100-clock PWM period.
            for (i = 0; i < 100; i = i + 1) begin
                @(negedge clk);
                if (pwm_out)
                    high_count = high_count + 1;
            end

            if (high_count !== expected_percent) begin
                $display("FAIL PWM: expected=%0d%% measured=%0d%%",
                         expected_percent, high_count);
                errors = errors + 1;
            end else begin
                $display("PASS PWM: expected=%0d%% measured=%0d%%",
                         expected_percent, high_count);
            end
        end
    endtask

    initial begin
        errors = 0;
        reset_n = 0;
        cmd = 0;
        enable = 0;
        fault = 0;

        repeat (3) @(posedge clk);
        reset_n = 1;

        $display("");
        $display("========== PWM CONTROL TEST ==========");

        // Normal forward command
        enable = 1;
        fault = 0;
        check_control(25, 25, 0, 25);
        check_pwm(25);

        // Another normal command
        check_control(50, 50, 0, 50);
        check_pwm(50);

        // Upper limiter
        check_control(95, 90, 0, 90);
        check_pwm(90);

        // Reverse command
        check_control(-50, -50, 1, 50);
        check_pwm(50);

        // Lower limiter
        check_control(-120, -90, 1, 90);
        check_pwm(90);

        // Zero command
        check_control(0, 0, 0, 0);
        check_pwm(0);

        // Disable interlock
        cmd = 50;
        enable = 0;
        fault = 0;
        #1;
        check_pwm(0);
        $display("PASS enable=0 forces PWM OFF");

        // Fault interlock
        enable = 1;
        fault = 1;
        #1;
        check_pwm(0);
        $display("PASS fault=1 forces PWM OFF");

        $display("");

        if (errors == 0) begin
            $display("======================================");
            $display("ALL TESTS PASSED");
            $display("======================================");
            $finish;
        end else begin
            $display("======================================");
            $display("TEST FAILED: %0d error(s)", errors);
            $display("======================================");
            $fatal(1);
        end
    end

endmodule