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--

-- SNESpad controller core

--

-- $Id: snespad_ctrl.vhd,v 1.1 2004-10-05 17:01:27 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 snespad_ctrl is

  generic (

    reset_level_g    :     natural := 0;

    clocks_per_6us_g :     natural := 6

  );

  port (

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

    clk_i            : in  std_logic;

    reset_i          : in  std_logic;

    clk_en_o         : out boolean;

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

    shift_buttons_o  : out boolean;

    save_buttons_o   : out boolean;

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

    pad_clk_o        : out std_logic;

    pad_latch_o      : out std_logic

  );

end snespad_ctrl;

use work.snespad_pack.all;

architecture rtl of snespad_ctrl is

  subtype  clocks_per_6us_t is natural range 0 to clocks_per_6us_g;

  type state_t is (IDLE,

                   IDLE2,

                   LATCH,

                   CLOCK,

                   READ_PAD);

  signal pad_latch_q,

         pad_latch_s  : std_logic;

  signal pad_clk_q,

         pad_clk_s  : std_logic;

  signal num_buttons_read_q : num_buttons_read_t;

  signal clocks_per_6us_q : clocks_per_6us_t;

  signal state_q,

         state_s  : state_t;

  signal clk_en_s        : boolean;

  signal shift_buttons_s : boolean;

begin

  -- pragma translate_off

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

  -- Check generics

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

  assert (reset_level_g = 0) or (reset_level_g = 1)

    report "reset_level_g must be either 0 or 1!"

    severity failure;

  assert clocks_per_6us_g > 1

    report "clocks_per_6us_g must be at least 2!"

    severity failure;

  -- pragma translate_on

  seq: process (reset_i, clk_i)

    variable clocks_per_6us_overflow_v : boolean;

  begin

    if reset_i = reset_level_g then

      pad_latch_q <= '1';

      pad_clk_q   <= '1';

      num_buttons_read_q <= num_buttons_c-1;

      clocks_per_6us_q  <= 0;

      state_q     <= IDLE;

    elsif clk_i'event and clk_i = '1' then

      if clk_en_s then

        clocks_per_6us_q <= 0;

      else

        clocks_per_6us_q <= clocks_per_6us_q + 1;

      end if;

      if clk_en_s and shift_buttons_s then

        if num_buttons_read_q = 0 then

          num_buttons_read_q <= num_buttons_c-1;

        else

          num_buttons_read_q <= num_buttons_read_q - 1;

        end if;

      end if;

      if clk_en_s then

        state_q <= state_s;

      end if;

      pad_clk_q   <= pad_clk_s;

      pad_latch_q <= pad_latch_s;

    end if;

  end process;

  clk_en_s <=  clocks_per_6us_q = clocks_per_6us_g-1;

  fsm: process (state_q,

                num_buttons_read_q)

  begin

    -- default assignments

    pad_clk_s       <= '1';

    pad_latch_s     <= '1';

    shift_buttons_s <= false;

    save_buttons_o  <= false;

    state_s         <= IDLE;

    case state_q is

      when IDLE =>

        save_buttons_o <= true;

        state_s        <= IDLE2;

      when IDLE2 =>

        state_s <= LATCH;

      when LATCH =>

        pad_latch_s <= '0';

        state_s     <= READ_PAD;

      when READ_PAD =>

        pad_latch_s <= '0';

        -- set clock low

        -- pad data will be read at end of 6us cycle

        pad_clk_s   <= '0';

        shift_buttons_s <= true;

        if num_buttons_read_q = 0 then

          -- return to IDLE after last button bit has been read

          state_s <= IDLE;

        else

          state_s <= LATCH;

        end if;

      when others =>

        null;

    end case;

  end process fsm;

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

  -- Output Mapping

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

  clk_en_o        <= clk_en_s;

  shift_buttons_o <= shift_buttons_s;

  pad_clk_o       <= pad_clk_q;

  pad_latch_o     <= pad_latch_q;

end rtl;

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-- File History:

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