Subversion Repositories t48

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--

-- The Program Memory control unit.

-- All operations related to the Program Memory are managed here.

--

-- $Id: pmem_ctrl.vhd,v 1.4 2005-06-08 19:13:53 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.pmem_addr_t;

use work.t48_pack.word_t;

use work.pmem_ctrl_pack.pmem_addr_ident_t;

entity pmem_ctrl 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_pcl_i       : in  boolean;

    read_pcl_i        : in  boolean;

    write_pch_i       : in  boolean;

    read_pch_i        : in  boolean;

    inc_pc_i          : in  boolean;

    write_pmem_addr_i : in  boolean;

    addr_type_i       : in  pmem_addr_ident_t;

    read_pmem_i       : in  boolean;

    -- Porgram Memroy Interface -----------------------------------------------

    pmem_addr_o       : out pmem_addr_t;

    pmem_data_i       : in  word_t

  );

end pmem_ctrl;

library ieee;

use ieee.numeric_std.all;

use work.pmem_ctrl_pack.all;

use work.t48_pack.res_active_c;

use work.t48_pack.clk_active_c;

use work.t48_pack.bus_idle_level_c;

use work.t48_pack.pmem_addr_width_c;

use work.t48_pack.dmem_addr_width_c;

use work.t48_pack.page_t;

architecture rtl of pmem_ctrl is

  -- implemented counter width of Program Counter

  -- the upper bit is only altered by JMP, CALL and RET(R)

  subtype pc_count_range_t is natural range pmem_addr_width_c-2 downto 0;

  -- the Program Counter

  signal program_counter_q : unsigned(pmem_addr_t'range);

  -- the Program Memory address

  signal pmem_addr_s,

         pmem_addr_q       : std_logic_vector(pmem_addr_t'range);

begin

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

  -- Process program_counter

  --

  -- Purpose:

  --   Implements the Program Counter.

  --

  program_counter: process (res_i, clk_i)

  begin

    if res_i = res_active_c then

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

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

    elsif clk_i'event and clk_i = clk_active_c then

      if en_clk_i then

        -- parallel load mode

        if write_pcl_i then

          program_counter_q(data_i'range) <= UNSIGNED(data_i);

        elsif write_pch_i then

          program_counter_q(pmem_addr_width_c-1 downto data_i'high+1) <=

            UNSIGNED(data_i(pmem_addr_width_c - dmem_addr_width_c - 1 downto 0));

        elsif inc_pc_i then

          -- increment mode

          -- the MSB is not modified by linear increments

          -- it can only be altered by JMP, CALL or RET(R)

          program_counter_q(pc_count_range_t) <=

            program_counter_q(pc_count_range_t) + 1;

        end if;

        -- set pmem address

        if write_pmem_addr_i then

          pmem_addr_q <= pmem_addr_s;

        end if;

      end if;

    end if;

  end process program_counter;

  --

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

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

  -- Process pmem_addr

  --

  -- Purpose:

  --   Multiplex the Program Memory address.

  --

  pmem_addr: process (program_counter_q,

                      addr_type_i,

                      pmem_addr_q,

                      data_i)

  begin

    -- default assignment

    pmem_addr_s <= STD_LOGIC_VECTOR(program_counter_q);

    case addr_type_i is

      when PM_PC =>

        -- default is ok

        null;

      when PM_PAGE =>

        pmem_addr_s(word_t'range) <= data_i;

        -- take page address from program counter

        --   => important for JMPP, MOVP!

        --      they must wrap to next page when at FF!

      when PM_PAGE3 =>

        pmem_addr_s(word_t'range) <= data_i;

        -- page address is explicitely specified

        pmem_addr_s(page_t'range) <= "0011";

      when others =>

        null;

    end case;

  end process pmem_addr;

  --

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

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

  -- Process data_output

  --

  -- Purpose:

  --   Multiplex the data bus output.

  --

  data_output: process (read_pmem_i,

                        read_pcl_i,

                        read_pch_i,

                        pmem_data_i,

                        program_counter_q)

  begin

    data_o <= (others => bus_idle_level_c);

    if read_pmem_i then

      data_o <= pmem_data_i;

    elsif read_pcl_i then

      data_o <= STD_LOGIC_VECTOR(program_counter_q(data_o'range));

    elsif read_pch_i then

      data_o(3 downto 0) <= STD_LOGIC_VECTOR(program_counter_q(pmem_addr_width_c-1 downto data_o'high+1));

    end if;

  end process data_output;

  --

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

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

  -- Output Mapping.

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

  pmem_addr_o <= pmem_addr_q;

end rtl;

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

-- File History:

--

-- $Log: not supported by cvs2svn $

-- Revision 1.3  2004/07/11 16:51:33  arniml

-- cleanup copyright notice

--

-- Revision 1.2  2004/04/24 23:44:25  arniml

-- move from std_logic_arith to numeric_std

--

-- Revision 1.1  2004/03/23 21:31:53  arniml

-- initial check-in

--

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