Q2a：FSM

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module top_module (
    input clk,
    input reset,   // Synchronous active-high reset
    input w,
    output z
);

    parameter A = 3'd0, B = 3'd1, C = 3'd2;
    parameter D = 3'd3, E = 3'd4, F = 3'd5;
    reg [2:0] current_state, next_state;

    always @(*) begin
        case(current_state)
            A:      next_state = w ? B : A;
            B:      next_state = w ? C : D;
            C:      next_state = w ? E : D;
            D:      next_state = w ? F : A;
            E:      next_state = w ? E : D;
            F:      next_state = w ? C : D;
            default:next_state = A;
        endcase
    end

    always @(posedge clk) begin
        if(reset) begin
            current_state <= A;
        end
        else begin
            current_state <= next_state;
        end
    end

    assign z = (current_state == E) | (current_state == F);

endmodule