Subversion Repositories t48

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

--

-- The Clock Control unit.

-- Clock States and Machine Cycles are generated here.

--

-- $Id: clock_ctrl.vhd,v 1.4 2004-04-24 23:44:25 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.all;

entity clock_ctrl is

  generic (

    -- divide XTAL1 by 3 to derive Clock States

    xtal_div_3_g : integer := 1

  );

  port (

    clk_i          : in  std_logic;

    xtal_i         : in  std_logic;

    res_i          : in  std_logic;

    en_clk_i       : in  boolean;

    xtal3_o        : out boolean;

    multi_cycle_i  : in  boolean;

    assert_psen_i  : in  boolean;

    assert_prog_i  : in  boolean;

    assert_rd_i    : in  boolean;

    assert_wr_i    : in  boolean;

    mstate_o       : out mstate_t;

    second_cycle_o : out boolean;

    ale_o          : out boolean;

    psen_o         : out boolean;

    prog_o         : out boolean;

    rd_o           : out boolean;

    wr_o           : out boolean

  );

end clock_ctrl;

library ieee;

use ieee.numeric_std.all;

architecture rtl of clock_ctrl is

  -- The three XTAL1 cycles.

  signal xtal_q  : unsigned(1 downto 0);

  signal xtal1_s,

         xtal2_s,

         xtal3_s : boolean;

  signal x1_s,

         x2_s,

         x3_s    : std_logic;

  -- The five clock states.

  signal mstate_q  : mstate_t;

  signal ale_q     : boolean;

  signal psen_q    : boolean;

  signal prog_q    : boolean;

  signal rd_q      : boolean;

  signal wr_q      : boolean;

  -- The Machine Cycle marker.

  signal second_cycle_q : boolean;

  signal multi_cycle_q  : boolean;

begin

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

  -- Verify the generics

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

  -- pragma translate_off

  -- XTAL1 divide by 3 --------------------------------------------------------

  assert (xtal_div_3_g = 1) or (xtal_div_3_g = 0)

    report "xtal_div_3_g must be either 1 or 0!"

    severity failure;

  -- pragma translate_on

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

  -- Divide XTAL1 by 3 to derive Clock States.

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

  use_xtal_div: if xtal_div_3_g = 1 generate

    xtal: process (res_i, xtal_i)

    begin

      if res_i = res_active_c then

        xtal_q <= TO_UNSIGNED(0, 2);

      elsif xtal_i'event and xtal_i = clk_active_c then

        if xtal_q < 2 then

          xtal_q <= xtal_q + 1;

        else

          xtal_q <= TO_UNSIGNED(0, 2);

        end if;

      end if;

    end process xtal;

    x1_s <=   '1'

            when xtal_q = 0 else

              '0';

    x2_s <=   '1'

            when xtal_q = 1 else

              '0';

    x3_s <=   '1'

            when xtal_q = 2 else

              '0';

  end generate;

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

  -- XTAL1 is used directly for Clock States.

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

  no_xtal_div: if xtal_div_3_g = 0 generate

    xtal_q <= TO_UNSIGNED(0, 2);

    x1_s <= '1';

    x2_s <= '1';

    x3_s <= '1';

  end generate;

  -- And finally the boolean flags --------------------------------------------

  xtal1_s <= to_boolean(x1_s);

  xtal2_s <= to_boolean(x2_s);

  xtal3_s <= to_boolean(x3_s);

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

  -- Process external_signal

  --

  -- Purpose:

  --   Control signals ALE, PSEN, PROG and RD/WR are generated here.

  --

  external_signals: process (res_i, xtal_i)

  begin

    if res_i = res_active_c then

      ale_q    <= false;

      psen_q   <= false;

      prog_q   <= false;

      rd_q     <= false;

      wr_q     <= false;

    elsif xtal_i'event and xtal_i = clk_active_c then

      case mstate_q is

        when MSTATE5 =>

          -- RD, WR are set at the end of XTAL2 of first machine cycle

          if xtal2_s and not second_cycle_q then

            if assert_rd_i then

              rd_q <= true;

            end if;

            if assert_wr_i then

              wr_q <= true;

            end if;

          end if;

        when MSTATE1 =>

          if xtal3_s then

             psen_q   <= false;

           end if;

        when MSTATE2 =>

          if xtal2_s then

            -- RD, WR are removed at the end of XTAL3 of second machine cycle

            rd_q     <= false;

            wr_q     <= false;

            -- PROG is removed at the and of XTAL3 of second machine cycle

            prog_q   <= false;

          end if;

        when MSTATE3 =>

          -- ALE is set at the end of XTAL2 of every machine cycle

          if xtal2_s then

            ale_q    <= true;

          end if;

        when MSTATE4 =>

          if xtal3_s then

            -- PSEN is set at the end of XTAL3

            if assert_psen_i then

              psen_q <= true;

            end if;

          end if;

          -- PROG is set at the and of XTAL2

          if xtal2_s and multi_cycle_q and not second_cycle_q and

            assert_prog_i then

            prog_q <= true;

          end if;

          -- ALE is removed at the end of XTAL2 of every machine cycle

          if xtal2_s then

            ale_q    <= false;

          end if;

      when others =>

        -- recover when states are out of sync

        ale_q    <= false;

        psen_q   <= false;

        prog_q   <= false;

        rd_q     <= false;

        wr_q     <= false;

      end case;

    end if;

  end process external_signals;

  --

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

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

  -- Process states

  --

  -- Purpose:

  --   The Clock State controller.

  --

  states: process (res_i, clk_i)

  begin

    if res_i = res_active_c then

      -- Reset machine state to MSTATE3

      -- This allows a proper instruction fetch for the first real instruction

      -- after reset.

      -- The MSTATE3 is part of a virtual NOP that has no MSTATE1 and MSTATE2.

      mstate_q <= MSTATE3;

    elsif clk_i'event and clk_i = clk_active_c then

      if en_clk_i then

        case mstate_q is

          when MSTATE5 =>

            mstate_q <= MSTATE1;

          when MSTATE1 =>

            mstate_q <= MSTATE2;

          when MSTATE2 =>

            mstate_q <= MSTATE3;

          when MSTATE3 =>

            mstate_q <= MSTATE4;

          when MSTATE4 =>

            mstate_q <= MSTATE5;

          when others =>

            -- recover when states are out of sync

            mstate_q <= MSTATE1;

            -- pragma translate_off

            assert false

              report "Encoding of Clock States failed!"

              severity error;

            -- pragma translate_on

        end case;

      end if;

    end if;

  end process states;

  --

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

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

  -- Process machine_cycle

  --

  -- Purpose:

  --   Keep track of machine cycles.

  --   Basically, this means to differ between first and second cycle.

  --

  machine_cycle: process (res_i, clk_i)

    variable state2_v, state5_v : boolean;

  begin

    if res_i = res_active_c then

      multi_cycle_q  <= false;

      second_cycle_q <= false;

    elsif clk_i'event and clk_i = clk_active_c then

      if en_clk_i then

        state2_v := mstate_q = MSTATE2;

        state5_v := mstate_q = MSTATE5;

        -- multi cycle information is delivered in State 2 from the decoder

        if state2_v and multi_cycle_i then

          multi_cycle_q <= true;

        end if;

        -- mark second machine cycle

        if multi_cycle_q and state5_v then

          second_cycle_q <= true;

        end if;

        -- reset at end of second machine cycle

        if state5_v and

           (multi_cycle_q and second_cycle_q) then

          multi_cycle_q  <= false;

          second_cycle_q <= false;

        end if;

      end if;

    end if;

  end process machine_cycle;

  --

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

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

  -- Output assignments

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

  xtal3_o        <= xtal3_s;

  mstate_o       <= mstate_q;

  second_cycle_o <= second_cycle_q;

  ale_o          <= ale_q;

  psen_o         <= psen_q;

  prog_o         <= prog_q;

  rd_o           <= rd_q;

  wr_o           <= wr_q;

end rtl;

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

-- File History:

--

-- $Log: not supported by cvs2svn $

-- Revision 1.3  2004/04/18 18:56:23  arniml

-- reset machine state to MSTATE3 to allow proper instruction fetch

-- after reset

--

-- Revision 1.2  2004/03/28 12:55:06  arniml

-- move code for PROG out of if-branch for xtal3_s

--

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

-- initial check-in

--

--

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