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--

-- GCpad controller core

--

-- $Id: gcpad_sampler.vhd,v 1.2 2004-10-08 21:35:08 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/gamepads/

--

-- The project homepage is located at:

--      http://www.opencores.org/projects.cgi/web/gamepads/overview

--

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library ieee;

use ieee.std_logic_1164.all;

entity gcpad_sampler is

  generic (

    reset_level_g      :     integer := 0;

    clocks_per_1us_g   :     integer := 2

  );

  port (

    clk_i              : in  std_logic;

    reset_i            : in  std_logic;

    wrap_sample_i      : in  boolean;

    sync_sample_i      : in  boolean;

    sample_underflow_o : out boolean;

    pad_data_i         : in  std_logic;

    pad_data_o         : out std_logic;

    sample_o           : out std_logic

  );

end gcpad_sampler;

use work.gcpad_pack.all;

architecture rtl of gcpad_sampler is

  signal pad_data_sync_q : std_logic_vector(1 downto 0);

  signal pad_data_s      : std_logic;

  constant cnt_sample_high_c  : natural := clocks_per_1us_g * 4 - 1;

  subtype  cnt_sample_t       is natural range 0 to cnt_sample_high_c;

  signal   cnt_zeros_q        : cnt_sample_t;

  signal   cnt_ones_q         : cnt_sample_t;

  signal   sample_underflow_q : boolean;

  signal   more_ones_q    : boolean;

begin

  seq: process (reset_i, clk_i)

    variable dec_timeout_v : boolean;

  begin

    if reset_i = reset_level_g then

      cnt_zeros_q          <= cnt_sample_high_c;

      cnt_ones_q           <= cnt_sample_high_c;

      more_ones_q          <= false;

      sample_underflow_q   <= false;

      pad_data_sync_q      <= (others => '1');

    elsif clk_i'event and clk_i = '1' then

      -- synchronizer for pad data

      pad_data_sync_q(0) <= pad_data_i;

      pad_data_sync_q(1) <= pad_data_sync_q(0);

      -- sample counter

      dec_timeout_v := false;

      if sync_sample_i then

        -- explicit preload

        cnt_zeros_q     <= cnt_sample_high_c;

        cnt_ones_q      <= cnt_sample_high_c;

      else

        if cnt_zeros_q = 0 then

          if wrap_sample_i then

            cnt_zeros_q <= cnt_sample_high_c;

          end if;

          dec_timeout_v := true;

        elsif pad_data_s = '0' then

          cnt_zeros_q   <= cnt_zeros_q - 1;

        end if;

        if cnt_ones_q = 0 then

          if wrap_sample_i then

            cnt_ones_q  <= cnt_sample_high_c;

          end if;

          dec_timeout_v := true;

        elsif pad_data_s /= '0' then

          cnt_ones_q    <= cnt_ones_q - 1;

        end if;

      end if;

      if cnt_ones_q < cnt_zeros_q then

        more_ones_q <= true;

      else

        more_ones_q <= false;

      end if;

      -- detect sample underflow

      sample_underflow_q <= dec_timeout_v;

    end if;

  end process seq;

  pad_data_s <= pad_data_sync_q(1);

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

  -- Output mapping

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

  pad_data_o         <= pad_data_s;

  sample_o           <=   '1'

                        when more_ones_q else

                          '0';

  sample_underflow_o <= sample_underflow_q;

end rtl;

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