Subversion Repositories t400

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

--

-- The Arithmetic Logic Unit (ALU).

-- It contains the accumulator and the C flag.

--

-- $Id: t400_alu.vhd 179 2009-04-01 19:48:38Z arniml $

--

-- Copyright (c) 2006 Arnim Laeuger (arniml@opencores.org)

--

-- All rights reserved

--

-- Redistribution and use in source and synthezised forms, with or without

-- modification, are permitted provided that the following conditions are met:

--

-- Redistributions of source code must retain the above copyright notice,

-- this list of conditions and the following disclaimer.

--

-- Redistributions in synthesized form must reproduce the above copyright

-- notice, this list of conditions and the following disclaimer in the

-- documentation and/or other materials provided with the distribution.

--

-- Neither the name of the author nor the names of other contributors may

-- be used to endorse or promote products derived from this software without

-- specific prior written permission.

--

-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 OR CONTRIBUTORS 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.

--

-- Please report bugs to the author, but before you do so, please

-- make sure that this is not a derivative work and that

-- you have the latest version of this file.

--

-- The latest version of this file can be found at:

--      http://www.opencores.org/cvsweb.shtml/t400/

--

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

library ieee;

use ieee.std_logic_1164.all;

use work.t400_pack.all;

use work.t400_opt_pack.all;

entity t400_alu is

  generic (

    opt_cko_g : integer := t400_opt_cko_crystal_c

  );

  port (

    -- System Interface -------------------------------------------------------

    ck_i       : in  std_logic;

    ck_en_i    : in  boolean;

    por_i      : in  boolean;

    res_i      : in  boolean;

    cko_i      : in  std_logic;

    -- Control Interface ------------------------------------------------------

    op_i       : in  alu_op_t;

    -- Data Interface ---------------------------------------------------------

    m_i        : in  dw_t;

    dec_data_i : in  dec_data_t;

    q_low_i    : in  dw_t;

    b_i        : in  b_t;

    g_i        : in  dw_t;

    in_i       : in  dw_t;

    sio_i      : in  dw_t;

    a_o        : out dw_t;

    carry_o    : out std_logic;

    c_o        : out std_logic

  );

end t400_alu;

library ieee;

use ieee.numeric_std.all;

architecture rtl of t400_alu is

  subtype alu_dw_t     is unsigned(dw_t'high+1 downto 0);

  signal  alu_result_s : alu_dw_t;

  signal  a_q          : dw_t;

  signal  c_q          : std_logic;

begin

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

  -- Process regs

  --

  -- Purpose:

  --   Implements the sequential registers of the ALU:

  --     * A - accumulator

  --     * C - carry flag

  --

  regs: process (ck_i, por_i)

  begin

    if por_i then

      a_q <= (others => '0');

      c_q <= '0';

    elsif ck_i'event and ck_i = '1' then

      if res_i then

        -- synchronous reset upon external reset event

        a_q <= (others => '0');

        c_q <= '0';

      elsif ck_en_i then

        -- update accumulator

        case op_i is

          when ALU_CLRA    |

               ALU_ADD     |

               ALU_ADD_10  |

               ALU_ADD_C   |

               ALU_ADD_DEC |

               ALU_COMP    |

               ALU_XOR     =>

            a_q <= std_logic_vector(alu_result_s(dw_t'range));

          when ALU_LOAD_M =>

            a_q <= m_i;

          when ALU_LOAD_Q =>

            a_q <= q_low_i;

          when ALU_LOAD_G =>

            a_q <= g_i;

          when ALU_LOAD_IN =>

            a_q <= in_i;

          when ALU_LOAD_IL =>

            a_q(3) <= in_i(3);

            if opt_cko_g = t400_opt_cko_gpi_c then

              a_q(2) <= cko_i;

            else

              a_q(2) <= '1';

            end if;

            a_q(1) <= '0';

            a_q(0) <= in_i(0);

          when ALU_LOAD_BR =>

            a_q(3 downto 2) <= (others => '0');

            a_q(1 downto 0) <= b_i(br_range_t);

          when ALU_LOAD_BD =>

            a_q <= b_i(bd_range_t);

          when ALU_LOAD_SIO =>

            a_q <= sio_i;

          when others =>

            null;

        end case;

        -- update C flag upon the following instructions

        case op_i is

          -- carry result of addition -----------------------------------------

          when ALU_ADD_C =>

            c_q <= alu_result_s(alu_dw_t'high);

          -- reset C flag -----------------------------------------------------

          when ALU_RC =>

            c_q <= '0';

          -- set C flag -------------------------------------------------------

          when ALU_SC =>

            c_q <= '1';

          when others =>

            null;

        end case;

      end if;

    end if;

  end process regs;

  --

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

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

  -- Process dp

  --

  -- Purpose:

  --   Implements the ALU's data path.

  --

  dp: process (op_i,

               a_q,

               m_i,

               dec_data_i,

               c_q)

    variable in1_v,

             in2_v,

             in3_v,

             add_v, xor_v : alu_dw_t;

  begin

    -- prepare adder

    in1_v      := '0' & unsigned(a_q);

    if    op_i = ALU_ADD_10 then

      in2_v    := to_unsigned(10, alu_dw_t'length);

    elsif op_i = ALU_ADD_DEC then

      in2_v    := '0' & unsigned(dec_data_i(dw_t'range));

    else

      in2_v    := '0' & unsigned(m_i);

    end if;

    if op_i = ALU_ADD_C then

      in3_v    := (others => '0');

      in3_v(0) := c_q;

    else

      in3_v    := (others => '0');

    end if;

    add_v := in1_v + in2_v + in3_v;

    -- prepare exclusive or

    xor_v := in1_v xor in2_v;

    case op_i is

      -- ALU operation: Clear accumulator -------------------------------------

      when ALU_CLRA =>

        alu_result_s <= (others => '0');

      -- ALU operation: Add to accumulator ------------------------------------

      when ALU_ADD     |

           ALU_ADD_10  |

           ALU_ADD_C   |

           ALU_ADD_DEC =>

        alu_result_s <= add_v;

      -- ALU operation: Complement accumulator --------------------------------

      when ALU_COMP =>

        alu_result_s <= '0' & not unsigned(a_q);

      -- ALU operation: XOR to accumulator ------------------------------------

      when ALU_XOR =>

        alu_result_s <= xor_v;

      when others =>

        alu_result_s <= (others => '-');

    end case;

  end process dp;

  --

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

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

  -- Output mapping

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

  a_o     <= a_q;

  carry_o <= alu_result_s(alu_dw_t'high);

  c_o     <= c_q;

end rtl;