library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.NUMERIC_STD.ALL;

entity FSM is
    Port(Clk: in STD_LOGIC;
          Reset: out STD_LOGIC;
          Run: in STD_LOGIC;
          MOP: in STD_LOGIC_VECTOR (3 downto 0);
          Load_A: out STD_LOGIC;
          Load_B: out STD_LOGIC;
          Cin: out STD_LOGIC;
          ALUop: out STD_LOGIC_VECTOR (2 downto 0);
          Input_Select: out STD_LOGIC_VECTOR (2 downto 0);
          out_state: out STD_LOGIC_VECTOR (3 downto 0));
end FSM;

ARCHITECTURE Behavioral OF FSM IS
SIGNAL y_present, y_next : STD_LOGIC_VECTOR(4 DOWNTO 0);
CONSTANT S0  : STD_LOGIC_VECTOR(4 DOWNTO 0) := "10000";
CONSTANT S1  : STD_LOGIC_VECTOR(4 DOWNTO 0) := "01000";
CONSTANT S2  : STD_LOGIC_VECTOR(4 DOWNTO 0) := "00100";
CONSTANT S3  : STD_LOGIC_VECTOR(4 DOWNTO 0) := "00010";
CONSTANT S4  : STD_LOGIC_VECTOR(4 DOWNTO 0) := "00001";

BEGIN
    PROCESS (RUN, y_present)
    BEGIN
        if RUN='0' then
            y_next<=S0;
        elsif RUN='1' then
            CASE y_present IS
                WHEN S0 =>
                    y_next <= S1;
                WHEN S1 =>
                    y_next <= S2;
                WHEN S2 =>
                    y_next <= S3;
                WHEN S3 =>
                    y_next <= S4;
                WHEN S4 =>
                    y_next <= S4;
                WHEN OTHERS =>
                    y_next <= S0;
            END CASE;
        END IF;
    END PROCESS;

    process (Clk)
    begin

        if(Clk'EVENT and Clk = '1') then
            y_present <= y_next;
        end if;
    end PROCESS;

     process (y_present, MOP)
     begin

        if MOP = "0000" then -- nop
            if y_present = S0 then
                out_state <= "0000";
                Input_Select <= "000";
            elsif y_present = S1 then
                out_state <= "0001";
                Input_Select <= "100";
            elsif y_present = S2 then
                out_state <= "0010";
                Input_Select <= "000";
            elsif y_present = S3 then
                out_state <= "0100";
                Input_Select <= "000";
            else
                out_state <= "1000";
                Input_Select <= "000";
            end if;

                Load_A <= '0';
                Load_B <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '0';

        elsif MOP = "0001" then -- clear
            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Input_Select <= "000";
                Load_A <= '0';
                Load_B <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '1';

        elsif MOP = "0010" then -- load A
            if y_present = S1 then
                Input_Select <= "110";
                Load_A <= '1';
            else
                Input_Select <= "000";
                Load_A <= '0';
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_B <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '0';

        elsif MOP = "0011" then -- load B

            if y_present = S1 then
                Input_Select <= "110";
                Load_B <= '1';
            else
                Input_Select <= "000";
                Load_B <= '0';
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '0';

        elsif MOP = "0100" then -- BcopyA
            if y_present = S1 then
                Load_B <= '1';
            else
                Load_B <= '0';
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Input_Select <= "000";
                Load_A <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '0';

        elsif MOP = "0101" then -- Add2
            if y_present = S3 then
                Load_B <= '1';
                ALUop <= "001";
                Input_Select <= "100";
            else
                Load_B <= '0';
                ALUop <= "000";
                Input_Select <= "000";
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

            Load_A <= '0';
            Cin <= '0';
            Reset <= '0';

        elsif MOP = "0110" then -- Add21
            if y_present = S3 then
                Load_B <= '1';
                ALUop <= "001";
                Input_Select <= "100";
                Cin <= '1';
            else
                Load_B <= '0';
                ALUop <= "000";
                Input_Select <= "000";
                Cin <= '0';
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Reset <= '0';

        elsif MOP = "0111" then -- Add3
            if y_present = S1 then
                Input_Select <= "100";
                Load_A <= '0';
                Load_B <= '1';
                ALUop <= "001";
            elsif y_present = S2 then
                Input_Select <= "100";
                Load_A <= '1';
                Load_B <= '0';
                ALUop <= "000";
            elsif y_present = S3 then
                Input_Select <= "110";
                Load_A <= '0';
                Load_B <= '1';
                ALUop <= "001";
            else
                Input_Select <= "000";
                Load_A <= '0';
                Load_B <= '0';
                ALUop <= "000";
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Cin <= '0';
                Reset <= '0';

        elsif MOP = "1000" then -- SUB
            if y_present = S1 then
                Input_Select <= "101";
                Load_B <= '1'; -- Select BitFlip B, add 1 => 2's complement -B
                Cin <= '1';
                ALUop <= "001";
            else
                Input_Select <= "000";
                Load_B <= '0';
                Cin <= '0';
                ALUop <= "000";
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Reset <= '0';

        elsif MOP = "1001" then -- BINVB
            if y_present = S1 then
                Input_Select <= "101";
                Load_B <= '1';
            else
                Input_Select <= "000";
                Load_B <= '0';
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '0';

        elsif MOP = "1010" then -- BAND
            if y_present = S1 then
                Input_Select <= "100";
                Load_B <= '1';
                ALUop <= "101";
            else
                Input_Select <= "000";
                Load_B <= '0';
                ALUop <= "000";
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Cin <= '1';
                Reset <= '0';

        elsif MOP = "1011" then -- BOR
            if y_present = S1 then
                Input_Select <= "100";
                Load_B <= '1';
                ALUop <= "100";
            else
                Input_Select <= "000";
                Load_B <= '0';
                ALUop <= "000";
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Cin <= '0';
                Reset <= '0';

        elsif MOP = "1100" then -- BXOR
            if y_present = S1 then
                Input_Select <= "100";
                Load_B <= '1';
                ALUop <= "110";
            else
                Input_Select <= "000";
                Load_B <= '0';
                ALUop <= "000";
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Cin <= '1';
                Reset <= '0';

        elsif MOP = "1101" then -- BLSRA
            if y_present = S1 then
                Input_Select <= "010";
                Load_B <= '1';
            else
                Input_Select <= "000";
                Load_B <= '0';
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '0';

        elsif MOP = "1110" then -- BLSLA
            if y_present = S1 then
                Input_Select <= "001";
                Load_B <= '1';
            else
                Input_Select <= "000";
                Load_B <= '0';
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '0';

        elsif MOP= "1111" then -- BASRA
            if y_present = S1 then
                Input_Select <= "011";
                Load_B <= '1';
            else
                Input_Select <= "000";
                Load_B <= '0';
            end if;

            if y_present = S0 then
                out_state <= "0000";
            elsif y_present = S1 then
                out_state <= "0001";
            elsif y_present = S2 then
                out_state <= "0010";
            elsif y_present = S3 then
                out_state <= "0100";
            else
                out_state <= "1000";
            end if;

                Load_A <= '0';
                Cin <= '0';
                ALUop <= "000";
                Reset <= '0';
            end if;
    end process;
end Behavioral;