Subversion Repositories t48

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

--

-- The Arithmetic Logic Unit (ALU).

-- It contains the ALU core plus the Accumulator and the Temp Reg.

--

-- $Id: alu.vhd,v 1.5 2004-04-06 20:21:53 arniml Exp $

--

-- Copyright (c) 2004, 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/t48/

--

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

library ieee;

use ieee.std_logic_1164.all;

use work.t48_pack.word_t;

use work.alu_pack.alu_op_t;

entity alu is

  port (

    -- Global Interface -------------------------------------------------------

    clk_i              : in  std_logic;

    res_i              : in  std_logic;

    en_clk_i           : in  boolean;

    -- T48 Bus Interface ------------------------------------------------------

    data_i             : in  word_t;

    data_o             : out word_t;

    write_accu_i       : in  boolean;

    write_shadow_i     : in  boolean;

    write_temp_reg_i   : in  boolean;

    read_alu_i         : in  boolean;

    -- Decoder Interface ------------------------------------------------------

    carry_i            : in  std_logic;

    carry_o            : out std_logic;

    aux_carry_i        : in  std_logic;

    aux_carry_o        : out std_logic;

    alu_op_i           : in  alu_op_t;

    use_carry_i        : in  boolean;

    da_low_i           : in  boolean;

    da_high_i          : in  boolean;

    da_overflow_o      : out boolean;

    accu_low_i         : in  boolean;

    p06_temp_reg_i     : in  boolean;

    p60_temp_reg_i     : in  boolean

  );

end alu;

library ieee;

use ieee.std_logic_arith.all;

use work.t48_pack.clk_active_c;

use work.t48_pack.res_active_c;

use work.t48_pack.bus_idle_level_c;

use work.t48_pack.nibble_t;

use work.alu_pack.all;

-- pragma translate_off

use work.t48_tb_pack.tb_accu_s;

-- pragma translate_on

architecture rtl of alu is

  -- the Accumulator and Temp Reg

  signal accumulator_q,

         accu_shadow_q,

         temp_req_q     : word_t;

  -- inputs to the ALU core

  signal in_a_s,

         in_b_s  : word_t;

  -- output of the ALU core

  signal data_s  : word_t;

  signal add_result_s : alu_operand_t;

begin

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

  -- Process working_regs

  --

  -- Purpose:

  --   Implements the working registers:

  --    + Accumulator

  --    + Temp Reg

  --

  working_regs: process (res_i, clk_i)

  begin

    if res_i = res_active_c then

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

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

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

    elsif clk_i'event and clk_i = clk_active_c then

      if en_clk_i then

        if write_accu_i then

          if accu_low_i then

            accumulator_q(nibble_t'range) <= data_i(nibble_t'range);

          else

            accumulator_q <= data_i;

          end if;

        end if;

        if write_shadow_i then

          -- write shadow directly from t48 data bus

          accu_shadow_q <= data_i;

        else

          -- default: update shadow Accumulator from real Accumulator

          accu_shadow_q <= accumulator_q;

        end if;

        if p06_temp_reg_i then

          -- low nibble of DA sequence

          temp_req_q  <= "00000110";

        elsif p60_temp_reg_i then

          -- high nibble of DA sequence

          temp_req_q  <= "01100000";

        elsif write_temp_reg_i then

          -- normal load from T48 bus

          temp_req_q  <= data_i;

        end if;

      end if;

    end if;

  end process working_regs;

  --

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

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

  -- Build the inputs to the ALU core.

  -- Input A:

  --   Unary operators use only Input A.

  --   Is always fed from the shadow Accumulator.

  --   Assumption: It never happens that the Accumulator is written and then

  --               read for an ALU operation in the next cycle.

  --               Its contents can thus be staged through the shadow Accu.

  -- Input B:

  --   Is always fed from the Temp Reg.

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

  in_a_s <= accu_shadow_q;

  in_b_s <= temp_req_q;

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

  -- Process alu_core

  --

  -- Purpose:

  --   Implements the ALU core.

  --   All operations defined in alu_op_t are handled here.

  --

  alu_core: process (in_a_s,

                     in_b_s,

                     alu_op_i,

                     carry_i,

                     use_carry_i,

                     add_result_s)

  begin

    -- default assigments

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

    carry_o     <= '0';

    case alu_op_i is

      -- Operation: AND -------------------------------------------------------

      when ALU_AND =>

        data_s <= in_a_s and in_b_s;

      -- Operation: OR --------------------------------------------------------

      when ALU_OR =>

        data_s <= in_a_s or in_b_s;

      -- Operation: XOR -------------------------------------------------------

      when ALU_XOR =>

        data_s <= in_a_s xor in_b_s;

      -- Operation: Add -------------------------------------------------------

      when ALU_ADD =>

        data_s  <= add_result_s(data_s'range);

        carry_o <= add_result_s(add_result_s'high);

      -- Operation: CPL -------------------------------------------------------

      when ALU_CPL =>

        data_s <= not in_a_s;

      -- Operation: CLR -------------------------------------------------------

      when ALU_CLR =>

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

      -- Operation: RL --------------------------------------------------------

      when ALU_RL =>

        data_s(7 downto 1) <= in_a_s(6 downto 0);

        carry_o            <= in_a_s(7);

        if use_carry_i then

          data_s(0)        <= carry_i;

        else

          data_s(0)        <= in_a_s(7);

        end if;

      -- Operation: RR --------------------------------------------------------

      when ALU_RR =>

        data_s(6 downto 0) <= in_a_s(7 downto 1);

        carry_o            <= in_a_s(0);

        if use_carry_i then

          data_s(7)        <= carry_i;

        else

          data_s(7)        <= in_a_s(0);

        end if;

      -- Operation: Swap ------------------------------------------------------

      when ALU_SWAP =>

        data_s(3 downto 0) <= in_a_s(7 downto 4);

        data_s(7 downto 4) <= in_a_s(3 downto 0);

      -- Operation: DEC -------------------------------------------------------

      when ALU_DEC =>

        data_s <= add_result_s(data_s'range);

      -- Operation: INC -------------------------------------------------------

      when ALU_INC =>

        data_s <= add_result_s(data_s'range);

      -- Operation CONCAT -----------------------------------------------------

      when ALU_CONCAT =>

        data_s <= in_b_s(7 downto 4) & in_a_s(3 downto 0);

      -- Operation: NOP -------------------------------------------------------

      when ALU_NOP =>

        data_s <= in_a_s;

      when others =>

        -- pragma translate_off

        assert false

          report "Unknown ALU operation selected!"

          severity error;

        -- pragma translate_on

    end case;

  end process alu_core;

  --

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

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

  -- Process adder

  --

  -- Purpose:

  --   Implements the adder used by several instructions.

  --   This way of modelling the adder forces resource sharing of:

  --     * ADD

  --     * INC

  --     * DEC

  --

  adder: process (in_a_s,

                  in_b_s,

                  alu_op_i,

                  carry_i,

                  use_carry_i)

    variable add_a_v, add_b_v : alu_operand_t;

    variable result_v         : alu_operand_t;

    variable c_v              : std_logic;

    variable aux_c_v          : std_logic_vector(1 downto 0);

  begin

    -- Carry Selection --------------------------------------------------------

    if use_carry_i then

      c_v := carry_i;

    else

      c_v := '0';

    end if;

    -- Operand Selection ------------------------------------------------------

    -- defaults for ADD

    add_a_v := '0' & in_a_s;

    add_b_v := '0' & in_b_s;

    case alu_op_i is

      when ALU_INC =>

        add_b_v := "000000001";

      when ALU_DEC =>

        add_b_v := "111111111";

      when others =>

        null;

    end case;

    -- The Adder --------------------------------------------------------------

    result_v := UNSIGNED(add_a_v) +

                UNSIGNED(add_b_v) +

                CONV_UNSIGNED(c_v, alu_operand_t'length);

    add_result_s <= result_v;

    -- Auxiliary Carry --------------------------------------------------------

    aux_c_v           := in_a_s(4) & in_b_s(4);

    case aux_c_v is

      when "00" | "11" =>

        if result_v(4) = '1' then

          aux_carry_o <= '1';

        end if;

      when "01" | "10" =>

        if result_v(4) = '0' then

          aux_carry_o <= '1';

        end if;

      when others =>

          aux_carry_o <= '0';

        null;

    end case;

  end process adder;

  --

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

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

  -- Process da_overflow

  --

  -- Purpose:

  --   Detect overflow situation during DA sequence.

  --

  da_overflow: process (accu_shadow_q,

                        da_high_i)

    variable da_nibble_v : nibble_t;

    function da_overflow_f(data : in nibble_t) return boolean is

      variable overflow_v : boolean;

    begin

      case data is

        when "1010" |

             "1011" |

             "1100" |

             "1101" |

             "1110" |

             "1111" =>

          overflow_v := true;

        when others =>

          overflow_v := false;

      end case;

      return(overflow_v);

    end;

  begin

    if da_high_i then

      da_nibble_v := accu_shadow_q(7 downto 4);

    else

      da_nibble_v := accu_shadow_q(3 downto 0);

    end if;

    da_overflow_o <= da_overflow_f(da_nibble_v);

  end process da_overflow;

  --

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

  -- pragma translate_off

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

  -- Testbench support.

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

  tb_accu_s <= accumulator_q;

  -- pragma translate_on

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

  -- Output Multiplexer.

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

  data_o <=   data_s

            when read_alu_i else

              (others => bus_idle_level_c);

end rtl;

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

-- File History:

--

-- $Log: not supported by cvs2svn $

-- Revision 1.4  2004/04/06 18:10:41  arniml

-- rework adder and force resource sharing between ADD, INC and DEC

--

-- Revision 1.3  2004/04/04 14:18:52  arniml

-- add measures to implement XCHD

--

-- Revision 1.2  2004/03/28 21:08:51  arniml

-- support for DA instruction

--

-- Revision 1.1  2004/03/23 21:31:52  arniml

-- initial check-in

--

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