Subversion Repositories t400

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--

-- The serial input/output unit.

--

-- $Id: t400_sio.vhd,v 1.1.1.1 2006-05-06 01:56:45 arniml Exp $

--

-- 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/

--

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library ieee;

use ieee.std_logic_1164.all;

use work.t400_pack.all;

use work.t400_opt_pack.all;

entity t400_sio is

  generic (

    opt_so_output_type_g : integer := t400_opt_out_type_std_c;

    opt_sk_output_type_g : integer := t400_opt_out_type_std_c

  );

  port (

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

    ck_i       : in  std_logic;

    ck_en_i    : in  boolean;

    por_i      : in  boolean;

    res_i      : in  boolean;

    phi1_i     : in  std_logic;

    out_en_i   : in  boolean;

    in_en_i    : in  boolean;

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

    op_i       : in  sio_op_t;

    en0_i      : in  std_logic;

    en3_i      : in  std_logic;

    -- SIO Interface ----------------------------------------------------------

    a_i        : in  dw_t;

    c_i        : in  std_logic;

    sio_o      : out dw_t;

    -- Pad Interface ----------------------------------------------------------

    si_i       : in  std_logic;

    so_o       : out std_logic;

    so_en_o    : out std_logic;

    sk_o       : out std_logic;

    sk_en_o    : out std_logic

  );

end t400_sio;

library ieee;

use ieee.numeric_std.all;

use work.t400_io_pack.all;

architecture rtl of t400_sio is

  signal si_q       : std_logic;

  type   si_flt_t   is (SI_LOW_0, SI_LOW_1,

                        SI_HIGH_0, SI_HIGH_1);

  signal si_flt_s,

         si_flt_q   : si_flt_t;

  signal si_0_ok_s,

         si_1_ok_s  : boolean;

  signal si_0_ok_q,

         si_1_ok_q  : boolean;

  signal dec_sio_s  : boolean;

  signal new_sio_s,

         sio_q      : unsigned(dw_range_t);

  signal skl_q      : std_logic;

  signal so_s,

         sk_s       : std_logic;

  signal vdd_s      : std_logic;

begin

  vdd_s <= '1';

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

  -- Process seq

  --

  -- Purpose:

  --   Implements the sequential elements.

  --

  seq: process (ck_i, por_i)

  begin

    if    por_i then

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

      skl_q     <= '1';

      si_q      <= '1';

      si_flt_q  <= SI_LOW_0;

      si_0_ok_q <= false;

      si_1_ok_q <= false;

    elsif ck_i'event and ck_i = '1' then

      if res_i then

        -- synchronous reset upon external reset event

        skl_q <= '1';

      else

        if in_en_i then

          -- sample asynchronous SI input

          si_q      <= si_i;

        end if;

        if out_en_i then

          -- SI filter FSM

          si_flt_q  <= si_flt_s;

          -- SI low/high markers

          si_0_ok_q <= si_0_ok_s;

          si_1_ok_q <= si_1_ok_s;

        end if;

        -- SIO shift register / counter

        if    op_i = SIO_LOAD and ck_en_i then

          -- parallel update has priority

          sio_q <= unsigned(a_i);

          skl_q <= c_i;

        else

          sio_q <= new_sio_s;

        end if;

      end if;

    end if;

  end process seq;

  --

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

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

  -- Process new_sio

  --

  -- Purpose:

  --   Calculates the new value of SIO.

  --   Splitting this from the sequential process is required to deliver

  --   the transient new value of SIO to sio_o upon reading SIO.

  --

  new_sio: process (out_en_i,

                    en0_i,

                    sio_q,

                    dec_sio_s)

  begin

    -- default value

    new_sio_s <= sio_q;

    if out_en_i then

      if en0_i = '0' then

        -- shift register mode

        new_sio_s(3 downto 1) <= sio_q(2 downto 0);

        new_sio_s(0)          <= si_q;

      else

        -- counter mode

        if dec_sio_s then

          new_sio_s <= sio_q - 1;

        end if;

      end if;

    end if;

  end process new_sio;

  --

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

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

  -- Process si_sample

  --

  -- Purpose:

  --   Implements the low pass filter on SI for low and high levels.

  --

  si_sample: process (si_q,

                      si_flt_q,

                      si_0_ok_q, si_1_ok_q)

  begin

    -- default assignments

    si_flt_s  <= si_flt_q;

    si_0_ok_s <= si_0_ok_q;

    si_1_ok_s <= si_1_ok_q;

    dec_sio_s <= false;

    case si_flt_q is

      when SI_LOW_0 =>

        if si_q = '0' then

          si_flt_s  <= SI_LOW_1;

        else

          si_flt_s  <= SI_HIGH_0;

        end if;

      when SI_LOW_1 =>

        if si_q = '0' then

          si_0_ok_s <= true;            -- enough '0' on SI

          if not si_0_ok_q and si_1_ok_q then

            -- decrement counter if durations of high and low phases

            -- were long enough

            dec_sio_s <= true;

          end if;

        else

          si_flt_s  <= SI_HIGH_0;

          si_1_ok_s <= false;           -- restart measuring

        end if;

      when SI_HIGH_0 =>

        si_1_ok_s <= false;             -- restart marker

        if si_q = '1' then

          si_flt_s <= SI_HIGH_1;

        else

          si_flt_s <= SI_LOW_0;

        end if;

      when SI_HIGH_1 =>

        if si_q = '1' then

          si_1_ok_s   <= true;          -- enough '1' on SI

        else

          si_flt_s    <= SI_LOW_0;

          si_0_ok_s   <= false;         -- restart measuring

        end if;

      when others =>

        null;

    end case;

  end process si_sample;

  --

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

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

  -- Output mapping

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

  sio_o   <= std_logic_vector(new_sio_s);

  so_s    <= en3_i and (en0_i or sio_q(3));

  sk_s    <= skl_q and (en0_i or phi1_i);

  so_o    <= io_out_f(dat => so_s, opt => opt_so_output_type_g);

  so_en_o <= io_en_f (en  => vdd_s,

                      dat => so_s, opt => opt_so_output_type_g);

  sk_o    <= io_out_f(dat => sk_s, opt => opt_sk_output_type_g);

  sk_en_o <= io_en_f (en  => vdd_s,

                      dat => sk_s, opt => opt_sk_output_type_g);

end rtl;

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