library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity led is
port(clk:in std_logic; --時鐘信號
     rst:in std_logic; --系統復位信號
       q:out std_logic_vector(7 downto 0)); --接LED1~LED8
end;
architecture one of led is
    type states is(s0,s1,s2,s3); --定義4種模式
    signal present :states;
    signal q1:std_logic_vector(7 downto 0);
    signal count:std_logic_vector(3 downto 0);
begin
process(clk,rst)
begin
if rst='1' then --系統復位
    present<=s0;
    q1<=(others=>'0');
elsif clk'event and clk='1' then
    case present is
    when s0=>if q1="00000000" then --S0模式：從左到右逐個點亮LED
                 q1<="10000000";
             else
                 if count="0111" then
                     count<=(others=>'0');
                     q1<="00000001";
                     present<=s1;
                 else q1<=q1(0)&q1(7 downto 1);
                     count<=count+1;
                     present<=s0;
                 end if;
             end if;
    when s1=>if count="0111" then --S1模式：從右到左逐個點亮LED
                 count<=(others=>'0');
                 q1<="10000001";
                 present<=s2;
             else q1<=q1(6 downto 0)&q1(7);
                 count<=count+1;
                 present<=s1;
             end if;
    when s2=>if count="0111" then --S2模式：從兩邊到中間逐個點亮LED
                 count<=(others=>'0');
                 q1<="00011000";
                 present<=s3;
             else q1(7 downto 4)<=q1(4)&q1(7 downto 5); 
                 q1(3 downto 0)<=q1(2 downto 0)&q1(3);
                 count<=count+1;
                 present<=s2;
             end if;
    when s3=>if count="0111" then --S3模式：從中間到兩邊逐個點亮LED
                 count<=(others=>'0');
                 q1<="10000000";
                 present<=s0;
             else q1(7 downto 4)<=q1(6 downto 4)&q1(7); 
                 q1(3 downto 0)<=q1(0)&q1(3 downto 1);
                 count<=count+1;
                 present<=s3;
             end if;
    end case;
end if;
end process;
    q<=q1;
end;