Subversion Repositories mod_sim_exp

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----  adder_block                                                 ---- 

----                                                              ---- 

----  This file is part of the                                    ----

----    Modular Simultaneous Exponentiation Core project          ---- 

----    http://www.opencores.org/cores/mod_sim_exp/               ---- 

----                                                              ---- 

----  Description                                                 ---- 

----    Adder block with a flipflop for the carry out             ----

----    for use in the montgommery multiplier pre and post        ----

----    computation adders                                        ----

----                                                              ----

----  Dependencies:                                               ----

----    - cell_1b_adder                                           ----

----    - d_flip_flop                                             ----

----                                                              ---- 

----  Authors:                                                    ----

----      - Geoffrey Ottoy, DraMCo research group                 ----

----      - Jonas De Craene, JonasDC@opencores.org                ---- 

----                                                              ---- 

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----                                                              ---- 

---- Copyright (C) 2011 DraMCo research group and OPENCORES.ORG   ---- 

----                                                              ---- 

---- This source file may be used and distributed without         ---- 

---- restriction provided that this copyright statement is not    ---- 

---- removed from the file and that any derivative work contains  ---- 

---- the original copyright notice and the associated disclaimer. ---- 

----                                                              ---- 

---- This source file is free software; you can redistribute it   ---- 

---- and/or modify it under the terms of the GNU Lesser General   ---- 

---- Public License as published by the Free Software Foundation; ---- 

---- either version 2.1 of the License, or (at your option) any   ---- 

---- later version.                                               ---- 

----                                                              ---- 

---- This source is distributed in the hope that it will be       ---- 

---- useful, but WITHOUT ANY WARRANTY; without even the implied   ---- 

---- warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      ---- 

---- PURPOSE.  See the GNU Lesser General Public License for more ---- 

---- details.                                                     ---- 

----                                                              ---- 

---- You should have received a copy of the GNU Lesser General    ---- 

---- Public License along with this source; if not, download it   ---- 

---- from http://www.opencores.org/lgpl.shtml                     ---- 

----                                                              ---- 

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library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

library mod_sim_exp;

use mod_sim_exp.mod_sim_exp_pkg.all;

-- (width)-bit full adder block using cell_1b_adders

-- with buffered carry out

entity adder_block is

  generic (

    width : integer := 32 --adder operand widths

  );

  port (

    -- clock input

    core_clk : in std_logic;

    -- adder input operands a, b (width)-bit

    a : in std_logic_vector((width-1) downto 0);

    b : in std_logic_vector((width-1) downto 0);

    -- carry in, out

    cin   : in std_logic;

    cout  : out std_logic;

    -- adder result out (width)-bit

    r : out std_logic_vector((width-1) downto 0)

  );

end adder_block;

architecture Structural of adder_block is

  -- array for the carry bits

  signal carry : std_logic_vector(width downto 0);

begin

  -- carry in

  carry(0) <= cin;

  -- structure of (width) cell_1b_adders

  adder_chain : for i in 0 to (width-1) generate

    adders : cell_1b_adder

    port map(

      a    => a(i),

      b    => b(i),

      cin  => carry(i),

      cout => carry(i+1),

      r    => r(i)

    );

  end generate;

  -- buffer the carry every clock cycle

  carry_reg : d_flip_flop

  port map(

    core_clk => core_clk,

    reset    => '0',

    din      => carry(width),

    dout     => cout

  );

end Structural;