------------------------------------------------------------
-- Entity and architecture for a simple controller
--
-- This controller supports only multiplication of
--     UNSIGNED numbers
--     of unknown precision (MODE 3)
------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;
entity controller is
  port (clock, nReset : in std_logic;
        Start : in std_logic;
        LsbB, EmptyB, FullB : in std_logic;
        UpdateA, UpdateB, UpdateP, Shift, ZeroP, Subtract, EnableP: out std_logic
        );
end entity controller;

architecture behaviour of controller is

  signal state : std_logic_vector( 2 downto 0 );

begin

  state_machine: process(clock, nReset) is
    begin
      if (nReset = '0' ) then
        state <= (others => '0');
      elsif rising_edge(clock) then

        if state="000" then
          if Start='1' then
            state <= "001";
          end if;
        elsif state="001" then state <= "010";
        elsif state="010" then state <= "011";
        elsif state="011" then
          if EmptyB='1' then
            state <= "100";
          end if;
        else state <= "000";
        end if;

      end if;
    end process state_machine;

    UpdateA <= '1' when ( state="001" or state="011") else '0';
    UpdateB <= '1' when ( state="010" or state="011") else '0';
    Shift   <= '1' when state="011" else '0';
    ZeroP   <= '1' when state="001" else '0';
    EnableP <= '1' when state="100" else '0';
    Subtract <= '0';
    UpdateP <= '1' when (state="001" or (state="011" and LsbB='1')) else '0';

end architecture behaviour;