Sega Mega Driver controller

module SmdController
(
    input clk,
    input smd_select,
    output smd_data0, smd_data1, smd_data2, smd_data3, smd_data4, smd_data5,
    input button_a, button_b, button_c, button_x, button_y, button_z, button_up, button_down, button_left, button_right, button_start, button_mode
);

    reg [12:0] idle_counter;
    reg [1:0] select_counter;
    reg [1:0] select_counter_prev;

    wire reset = idle_counter == 0;

    assign smd_data0 = !select_counter[1] ?
                button_up :
                (!select_counter[0] ?
                    (smd_select ? button_up : 1'b0) :
                    (smd_select ? button_z : 1'b1)
                ); // Up/Z
    assign smd_data1 = !select_counter[1] ?
                button_down :
                (!select_counter[0] ?
                    (smd_select ? button_down : 1'b0) :
                    (smd_select ? button_y : 1'b1)
                ); // Down/Y
    assign smd_data2 = smd_select ? (select_counter[1:0] != 2'b11 ? button_left : button_x) : (select_counter[1:0] != 2'b11 ? 1'b0 : 1'b1); // Left/X
    assign smd_data3 = smd_select ? (select_counter[1:0] != 2'b11 ? button_right : button_mode) : (select_counter[1:0] != 2'b11 ? 1'b0 : 1'b1); //Right/Mode
    assign smd_data4 = smd_select ? button_b : button_a; // A/B
    assign smd_data5 = smd_select ? button_c : button_start; // Start/C

    always @ (posedge smd_select, posedge reset)
    begin
      if (reset)
        select_counter = 0;
      else
        select_counter = select_counter + 1'b1;
    end

    always @ (negedge clk)
    begin
        if (select_counter != select_counter_prev)
        begin
            select_counter_prev= select_counter;
            idle_counter = 1'b1;
        end else begin
          idle_counter = idle_counter + 1'b1;
        end
    end

endmodule