Subversion Repositories t400

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

--

-- The Program memory controller.

--

-- $Id: t400_pmem_ctrl.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_opt_pack.all;

use work.t400_pack.all;

entity t400_pmem_ctrl is

  generic (

    opt_type_g : integer := t400_opt_type_420_c

  );

  port (

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

    ck_i       : in  std_logic;

    ck_en_i    : in  boolean;

    por_i      : in  boolean;

    res_i      : in  boolean;

    a_i        : in  dw_t;

    m_i        : in  dw_t;

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

    op_i       : in  pc_op_t;

    dec_data_i : in  dec_data_t;

    -- Stack Interface --------------------------------------------------------

    pc_o       : out pc_t;

    pc_i       : in  pc_t;

    -- Program Memory Interface -----------------------------------------------

    pm_addr_o  : out pc_t

  );

end t400_pmem_ctrl;

library ieee;

use ieee.numeric_std.all;

-- pragma translate_off

use work.tb_pack.tb_pc_s;

-- pragma translate_on

architecture rtl of t400_pmem_ctrl is

  signal pc_q      : pc_t;

  signal last_pc_s : pc_t;

begin

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

  -- Determine last program counter address

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

  last_pc_s <=   to_unsigned(16#1ff#, pc_t'length)

               when opt_type_g = t400_opt_type_410_c else

                 to_unsigned(16#3ff#, pc_t'length);

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

  -- Process pc

  --

  -- Purpose:

  --   Implements the program counter.

  --

  pc: process (ck_i, por_i)

  begin

    if por_i then

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

    elsif ck_i'event and ck_i = '1' then

      if    res_i then

        -- synchronous reset upon external reset event

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

      elsif ck_en_i then

        -- determine PC update mode

        case op_i is

          -- increment program counter ----------------------------------------

          when PC_INC_PC =>

            if pc_q = last_pc_s then

              -- roll over

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

            else

              pc_q           <= pc_q + 1;

            end if;

          -- Load lower 6 bits from program memory data -----------------------

          when PC_LOAD_6 =>

            pc_q(5 downto 0) <= unsigned(dec_data_i(5 downto 0));

          -- Load lower 7 bits from program memory data -----------------------

          when PC_LOAD_7 =>

            pc_q(6 downto 0) <= unsigned(dec_data_i(6 downto 0));

          -- Load lower 8 bits from program memory data -----------------------

          when PC_LOAD_8 =>

            pc_q(7 downto 0) <= unsigned(dec_data_i(7 downto 0));

          -- Load all bits from program memory data ---------------------------

          when PC_LOAD =>

            pc_q             <= unsigned(dec_data_i);

          -- pop program counter from stack -----------------------------------

          when PC_POP =>

            pc_q             <= pc_i;

          -- update program counter for LQID instruction ----------------------

          when PC_LOAD_A_M =>

            pc_q(7 downto 4) <= unsigned(a_i);

            pc_q(3 downto 0) <= unsigned(m_i);

          -- load interrupt vector --------------------------------------------

          when PC_INT =>

            if opt_type_g = t400_opt_type_420_c then

              -- load address 0x100, i.e. skip first instruction at

              -- vector address 0x0ff which has to be a NOP :-)

              pc_q <= (8 => '1', others => '0');

            end if;

          when others =>

            null;

        end case;

      end if;

    end if;

  end process pc;

  --

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

  -- pragma translate_off

  -- instrument interrupt testbench

  tb_pc_s <= pc_q;

  -- pragma translate_on

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

  -- Output mapping

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

  pc_o      <= pc_q;

  pm_addr_o <= pc_q;

end rtl;