entity fg_a_05 is

end entity fg_a_05;


library ieee;  use ieee.std_logic_1164.all;

architecture test of fg_a_05 is

  signal clk, reset, a, b, x, q : std_ulogic;

begin

  -- code from book

  ff2 : process (reset, clk) is
  begin
    if reset = '1' then
      q <= '0';
    elsif rising_edge(clk) then
      if x = '1' then
        q <= a;
      else
        q <= b;
      end if;
    end if;
  end process ff2;

  -- end code from book

  stimulus : process is
  begin
    reset <= '0';  clk <= '0';  x <= '1'; a <= '1'; b <= '0';  wait for 10 ns;
    reset <= '1', '0' after 30 ns;
    clk <= '1' after 10 ns, '0' after 20 ns;
    wait for 40 ns;
    clk <= '1', '0' after 2 ns,
           '1' after 12 ns, '0' after 14 ns,
           '1' after 17 ns, '0' after 19 ns,
           '1' after 22 ns, '0' after 24 ns,
           '1' after 27 ns, '0' after 29 ns,
           '1' after 32 ns, '0' after 34 ns,
           '1' after 37 ns, '0' after 39 ns,
           '1' after 42 ns, '0' after 44 ns,
           '1' after 47 ns, '0' after 49 ns;
    a <= '0' after 10 ns, '1' after 20 ns, '0' after 30 ns, '1' after 40 ns;
    b <= '0' after 15 ns, '1' after 25 ns, '0' after 35 ns, '1' after 45 ns;
    x <= '0' after 30 ns;

    wait;
  end process stimulus;

end architecture test;