设计一个循环灯控制器，该控制器控制红、绿、黄三个发光管循环发亮。要求红发光管亮2秒，绿发光管亮3秒，黄发光管亮1秒。（假设外部提供频率为1MHz的方波信号）

library ieee;

use ieee.std_logic_1164.all;

entity loopled_tb_vhd is

end loopled_tb_vhd;

architecture rtl of loopled_tb_vhd is

  component loopled

    port(

       CLK,CLR:IN STD_LOGIC;

       Red,Green,Yellow:OUT STD_LOGIC

      );

  end component;

  signal clr  :std_logic:='0';

  signal clk  :std_logic:='0';

  signal Red  :std_logic;

  signal Green  :std_logic;

  signal Yellow  :std_logic;

  begin

    uut:loopled port map

    (

      clk=>clk,clr=>clr,Red=>Red,Green=>Green,Yellow=>Yellow

      );

  --clk_gen:process

  --begin

   -- clk <= '1' AFTER 0 ns;

    clr <='1' AFTER 0 ns,

         '0' AFTER 2 ns;

  tb:PROCESS

  BEGIN

    clk<='0';

    LOOP

        clk<='1','0' AFTER 1 ns;

        wait for 2 ns;

    END LOOP;

END PROCESS;

end rtl;