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-- ***** BEGIN LICENSE BLOCK *****

-- 

-- $Id: ARITHMETIC_UNIT.vhd,v 1.4 2006-10-05 16:17:11 petebleackley Exp $ $Name: not supported by cvs2svn $

-- *

-- * Version: MPL 1.1/GPL 2.0/LGPL 2.1

-- *

-- * The contents of this file are subject to the Mozilla Public License

-- * Version 1.1 (the "License"); you may not use this file except in compliance

-- * with the License. You may obtain a copy of the License at

-- * http://www.mozilla.org/MPL/

-- *

-- * Software distributed under the License is distributed on an "AS IS" basis,

-- * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for

-- * the specific language governing rights and limitations under the License.

-- *

-- * The Original Code is BBC Research and Development code.

-- *

-- * The Initial Developer of the Original Code is the British Broadcasting

-- * Corporation.

-- * Portions created by the Initial Developer are Copyright (C) 2004.

-- * All Rights Reserved.

-- *

-- * Contributor(s): Peter Bleackley (Original author)

-- *

-- * Alternatively, the contents of this file may be used under the terms of

-- * the GNU General Public License Version 2 (the "GPL"), or the GNU Lesser

-- * Public License Version 2.1 (the "LGPL"), in which case the provisions of

-- * the GPL or the LGPL are applicable instead of those above. If you wish to

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library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

use IEEE.NUMERIC_STD.ALL;

--  Uncomment the following lines to use the declarations that are

--  provided for instantiating Xilinx primitive components.

--library UNISIM;

--use UNISIM.VComponents.all;

entity ARITHMETIC_UNIT is

    Port ( DIFFERENCE : in std_logic_vector(15 downto 0);

           PROB : in std_logic_vector(7 downto 0);

                          LOW : in std_logic_vector(15 downto 0);

           ENABLE : in std_logic;

                          RESET :       in std_logic;

           CLOCK : in std_logic;

           DIFFERENCE_OUT0 : out std_logic_vector(15 downto 0);

                          DIFFERENCE_OUT1 : out std_logic_vector(15 downto 0);

           RESULT_OUT0 : out std_logic_vector(15 downto 0);

                          RESULT_OUT1 : out std_logic_vector(15 downto 0);

           DATA_LOAD : out std_logic :='1');

end ARITHMETIC_UNIT;

architecture RTL of ARITHMETIC_UNIT is

        signal LOW2 : std_logic_vector(16 downto 0);

        signal PRODUCT :        std_logic_vector (24 downto 0);

        signal PRODUCT2 :        std_logic_vector (16 downto 0);

        signal RESULT : std_logic_vector (16 downto 0);

        signal RESULT0 : std_logic_vector (16 downto 0);

        signal DIFFERENCE1 : std_logic_vector (16 downto 0);

        signal DIFFERENCE2 : std_logic_vector(16 downto 0);

        signal DIFFERENCE3 : std_logic_vector(16 downto 0);

        signal DIFFERENCE4 :    std_logic_vector(16 downto 0);

        signal DELAY1 : std_logic;

--      signal DELAY2 : std_logic;

        signal CALCULATE :      std_logic;

begin

-- The arithmetic

        DIFFERENCE2 <= ('0' & DIFFERENCE) + "00000000000000001";

MULTIPLY : process (CLOCK)

        begin

        if CLOCK'event and CLOCK = '1' then

                if ENABLE = '1' then

                PRODUCT <= DIFFERENCE2 * PROB;

                end if;

        end if;

end process MULTIPLY;

        PRODUCT2        <= PRODUCT(24 downto 8);

        RESULT <= LOW2 + PRODUCT2;

        RESULT_OUT1 <= RESULT(15 downto 0);

        RESULT0 <= (RESULT - "00000000000000001");

        RESULT_OUT0 <= RESULT0(15 downto 0);

        DIFFERENCE3 <= (PRODUCT2 - "00000000000000001");

        DIFFERENCE4 <= (DIFFERENCE1 - PRODUCT2);

        DIFFERENCE_OUT1 <= DIFFERENCE4(15 downto 0);

        DIFFERENCE_OUT0 <= DIFFERENCE3(15 downto 0);

-- Control logic

        CALCULATE <= ENABLE and not RESET;

        DATA_LOAD <= DELAY1;-- and DELAY2;

-- Sequential control logic

DELAYS: process (CLOCK)

        begin

        if CLOCK'event and CLOCK = '1' then

                DELAY1 <= CALCULATE;

--              DELAY2 <= DELAY1;

                if ENABLE = '1' then

                        DIFFERENCE1 <= '0' & DIFFERENCE;

                        LOW2 <= '0' & LOW;

                end if;

        end if;

end process DELAYS;

end RTL;