-- bigalu.vhd Version 2.0 by Dr. Jerry H. Tucker
-- Created  10/15/00 Worked     
-- entities BigALU
-- Uses alu in alu.vhd
LIBRARY IEEE;
USE work.all;
USE work.mips.all;
USE IEEE.Std_Logic_1164.all; 
--USE IEEE.std_logic_unsigned.all;
use ieee.std_logic_arith.all;
------------------------------------------------------------------------
--  ENTITY: BigALU - Connects 4 ALU slicess together to form a complete
--          ALU.
-- GENERIC: Width - The size of BigALU thee default is DWordSizr.
--          Width will me a multiple of 4  greater than 4.
--    PORT: SA - A input to the BigALU
--          SB - B input to the BigALU
--          ALU - Output of BigALU
--          Func - Function to be performeed by BigALU.
--                      "000" - and
--                      "001" - or
--                      "010" - add
--                      "110" - subtract
--                      "111" - set on lesss than
--           Overflow - Overflow signal
--           Zero     - If all bits of ALUU = 0 then Zero = '1' 
--                      else Zero = '0'
--   NEEDS: alu in alu.vhd
------------------------------------------------------------------------
ENTITY BigALU IS
    GENERIC(Width: Integer := DWordSize);
    PORT(SA, SB:    IN std_logic_vector(Width - 1 downto 0);
        ALU:        OUT std_logic_vector(Width - 1 downto 0);
        Func:       IN std_logic_vector(2 downto 0);
        Overflow:   OUT std_logic;
        Zero:       OUT std_logic
        );
END ENTITY BigALU;

ARCHITECTURE Struc OF BigALU IS
    CONSTANT Swidth: INTEGER := Width/4;
BEGIN  

    Zero <= Z(0) and Z(1) and Z(2) and Z(3); 

    PROCESS(Func) 
    BEGIN
        IF (Func = "110") OR (Func = "111") THEN
            InvB <= '1';
        ELSE
            InvB <= '0';
        END IF;        
    END PROCESS ;
  
 -- Least significant slice of ALU
    ALU0: ENTITY work.alu(behav)
            GENERIC MAP (Slice => 2) 
            PORT MAP
            (
                Ain => ,
                Bin => ,
                Cin => ,
                Result => ,
                Cout => ,
                Operation => ,
                Binvert => ,
                Less => ,
                Zero => 
            );
    ALU1: ENTITY work.alu(behav)
            GENERIC MAP (Slice => 2) 
            PORT MAP
            (
                Ain => ,
                Bin => ,
                Cin => ,
                Result => ,
                Cout => ,
                Operation => ,
                Binvert => ,
                Less => ,
                Zero => 
            );
    ALU2: ENTITY work.alu(behav)
            GENERIC MAP (Slice => 2) 
            PORT MAP
            (
                Ain => ,
                Bin => ,
                Cin => ,
                Result => ,
                Cout => ,
                Operation => ,
                Binvert => ,
                Less => ,
                Zero => 
            );
 -- Most significant slice of ALU
    ALU3: ENTITY work.alu(behav)
            GENERIC MAP (Slice => 2) 
            PORT MAP
            (
                Ain => ,
                Bin => ,
                Cin => ,
                Result => ,
                Cout => ,
                Operation => ,
                Binvert => ,
                Less => ,
                Set => ,
                Overflow => ,
                Zero => 
            );
END ARCHITECTURE Struc;