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-- $Id: folded_register.vhdl,v 1.1.1.1 2005-12-06 02:48:32 arif_endro Exp $

-------------------------------------------------------------------------------

-- Title       : Folded register. 

-- Project     : Mini AES 128 

-------------------------------------------------------------------------------

-- File        : folded_register.vhdl

-- Author      : "Arif E. Nugroho" <arif_endro@yahoo.com>

-- Created     : 2005/12/03

-- Last update : 

-- Simulators  : ModelSim SE PLUS 6.0

-- Synthesizers: ISE Xilinx 6.3i

-- Target      : 

-------------------------------------------------------------------------------

-- Description : Folded register manipulations for manipulating data.

-------------------------------------------------------------------------------

-- Copyright (C) 2005 Arif Endro Nugroho

-------------------------------------------------------------------------------

-- 

--         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 SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

-- IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF

-- MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO

-- EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

-- SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

-- PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;

-- OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,

-- WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR

-- OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF

-- ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

-- 

-------------------------------------------------------------------------------

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

entity folded_register is

  port (

    clk_i  : in  std_logic;

    enc_i  : in  std_logic;

    load_i : in  std_logic;

    data_i : in  std_logic_vector (127 downto 000);

    key_i  : in  std_logic_vector (127 downto 000);

    di_0_i : in  std_logic_vector (007 downto 000);

    di_1_i : in  std_logic_vector (007 downto 000);

    di_2_i : in  std_logic_vector (007 downto 000);

    di_3_i : in  std_logic_vector (007 downto 000);

    do_0_o : out std_logic_vector (007 downto 000);

    do_1_o : out std_logic_vector (007 downto 000);

    do_2_o : out std_logic_vector (007 downto 000);

    do_3_o : out std_logic_vector (007 downto 000)

    );

end folded_register;

architecture data_flow of folded_register is

  component counter2bit

    port (

      clock : in  std_logic;

      clear : in  std_logic;

      count : out std_logic_vector (1 downto 0)

      );

  end component;

  type fifo16x8 is array (00 to 15) of std_logic_vector (7 downto 0);

  type addr4x4 is array (3 downto 0) of std_logic_vector (3 downto 0);

  type addr4x8 is array (3 downto 0) of std_logic_vector (7 downto 0);

  signal foldreg0 : fifo16x8 :=

    (

      X"00", X"00", X"00", X"00", X"00", X"00", X"00", X"00",

      X"00", X"00", X"00", X"00", X"00", X"00", X"00", X"00"

      );

--

  signal foldreg1 : fifo16x8 :=

    (

      X"00", X"00", X"00", X"00", X"00", X"00", X"00", X"00",

      X"00", X"00", X"00", X"00", X"00", X"00", X"00", X"00"

      );

--

  signal foldreg2 : fifo16x8 :=

    (

      X"00", X"00", X"00", X"00", X"00", X"00", X"00", X"00",

      X"00", X"00", X"00", X"00", X"00", X"00", X"00", X"00"

      );

  signal   round0             : std_logic_vector (127 downto 000) := ( X"00000000_00000000_00000000_00000000" );

--

  signal   a_0_i              : std_logic_vector (3 downto 0)     := ( B"0000" );

  signal   a_1_i              : std_logic_vector (3 downto 0)     := ( B"0000" );

  signal   a_2_i              : std_logic_vector (3 downto 0)     := ( B"0000" );

  signal   a_3_i              : std_logic_vector (3 downto 0)     := ( B"0000" );

--

  constant fifo_addr_cons     : std_logic_vector (63 downto 00)   := ( X"05AF_49E3_8D27_C16B" );

  constant fifo_addr_cons_inv : std_logic_vector (63 downto 00)   := ( X"0DA7_41EB_852F_C963" );

  signal   fifo_addr          : std_logic_vector (63 downto 00)   := ( X"0000_0000_0000_0000" );

--

  signal   tmp                : addr4x8                           := ( X"00", X"00", X"00", X"00" );

  signal   addr               : addr4x4                           := ( X"0", X"0", X"0", X"0" );

--

  signal   count              : std_logic_vector (1 downto 0);

  signal   switch             : std_logic                         := '0';

  signal   reg_i              : std_logic                         := '0';

begin

  sect : counter2bit

    port map (

      clock => clk_i,

      clear => load_i,

      count => count

      );

  round0 <= data_i xor key_i;

  process(clk_i, load_i)

  begin

    if (load_i = '1') then

      foldreg0                 <= (

        round0 (127 downto 120), round0 (119 downto 112), round0 (111 downto 104), round0 (103 downto 096),

        round0 (095 downto 088), round0 (087 downto 080), round0 (079 downto 072), round0 (071 downto 064),

        round0 (063 downto 056), round0 (055 downto 048), round0 (047 downto 040), round0 (039 downto 032),

        round0 (031 downto 024), round0 (023 downto 016), round0 (015 downto 008), round0 (007 downto 000)

        );

--

      foldreg1                 <= (

        round0 (127 downto 120), round0 (119 downto 112), round0 (111 downto 104), round0 (103 downto 096),

        round0 (095 downto 088), round0 (087 downto 080), round0 (079 downto 072), round0 (071 downto 064),

        round0 (063 downto 056), round0 (055 downto 048), round0 (047 downto 040), round0 (039 downto 032),

        round0 (031 downto 024), round0 (023 downto 016), round0 (015 downto 008), round0 (007 downto 000)

        );

--

      if (enc_i = '0') then

        fifo_addr              <= fifo_addr_cons;

      else

        fifo_addr              <= fifo_addr_cons_inv;

      end if;

      reg_i                    <= '0';

    elsif (clk_i = '1' and clk_i'event) then

      if (reg_i = '1') then

        foldreg0 (00 to 11)    <= ( foldreg0 (04 to 15) );

        foldreg0 (12 to 15)    <= ( di_0_i, di_1_i, di_2_i, di_3_i );

      else

        foldreg1 (00 to 11)    <= ( foldreg1 (04 to 15) );

        foldreg1 (12 to 15)    <= ( di_0_i, di_1_i, di_2_i, di_3_i );

      end if;

      fifo_addr (63 downto 16) <= fifo_addr (47 downto 00);

      fifo_addr (15 downto 00) <= fifo_addr (63 downto 48);

      if (switch = '1') then

        reg_i                  <= not(reg_i);

      end if;

    end if;

  end process;

  a_0_i               <= addr(0);

  a_1_i               <= addr(1);

  a_2_i               <= addr(2);

  a_3_i               <= addr(3);

--

  foldreg2 (00 to 11) <= ( foldreg0 (04 to 15) )       when (reg_i = '1')    else ( foldreg1 (04 to 15) );

  foldreg2 (12 to 15) <= ( di_0_i, di_1_i, di_2_i, di_3_i );

--

  switch              <= (count(1)) and (count(0));

--

  addr(0)             <= fifo_addr (51 downto 48)      when ( load_i = '1' ) else fifo_addr (35 downto 32);

  addr(1)             <= fifo_addr (55 downto 52)      when ( load_i = '1' ) else fifo_addr (39 downto 36);

  addr(2)             <= fifo_addr (59 downto 56)      when ( load_i = '1' ) else fifo_addr (43 downto 40);

  addr(3)             <= fifo_addr (63 downto 60)      when ( load_i = '1' ) else fifo_addr (47 downto 44);

--

  tmp(0)              <= foldreg1(conv_integer(a_0_i)) when ( reg_i = '1' )  else foldreg0(conv_integer(a_0_i));

  tmp(1)              <= foldreg1(conv_integer(a_1_i)) when ( reg_i = '1' )  else foldreg0(conv_integer(a_1_i));

  tmp(2)              <= foldreg1(conv_integer(a_2_i)) when ( reg_i = '1' )  else foldreg0(conv_integer(a_2_i));

  tmp(3)              <= foldreg1(conv_integer(a_3_i)) when ( reg_i = '1' )  else foldreg0(conv_integer(a_3_i));

--

  do_0_o              <= tmp(3)                        when ( switch = '0')  else foldreg2(conv_integer(a_3_i));

  do_1_o              <= tmp(2)                        when ( switch = '0')  else foldreg2(conv_integer(a_2_i));

  do_2_o              <= tmp(1)                        when ( switch = '0')  else foldreg2(conv_integer(a_1_i));

  do_3_o              <= tmp(0)                        when ( switch = '0')  else foldreg2(conv_integer(a_0_i));

end data_flow;