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--  GECKO3COM IP Core

--

--  Copyright (C) 2009 by

--   ___    ___   _   _

--  (  _ \ (  __)( ) ( )

--  | (_) )| (   | |_| |   Bern University of Applied Sciences

--  |  _ < |  _) |  _  |   School of Engineering and

--  | (_) )| |   | | | |   Information Technology

--  (____/ (_)   (_) (_)

--

--  This program is free software: you can redistribute it and/or modify

--  it under the terms of the GNU General Public License as published by

--  the Free Software Foundation, either version 3 of the License, or

--  (at your option) any later version.

--

--  This program is distributed in the hope that it will be useful,

--  but WITHOUT ANY WARRANTY; without even the implied warranty of

--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

--  GNU General Public License for more details. 

--  You should have received a copy of the GNU General Public License

--  along with this program.  If not, see <http://www.gnu.org/licenses/>.

--

--  URL to the project description: 

--    http://labs.ti.bfh.ch/gecko/wiki/systems/gecko3com/start

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

--

--  Author:  Andreas Habegger, Christoph Zimmermann

--  Date of creation: 8. April 2009

--  Description:

--      FSM that controls the interface between the EZ-USB (and it's internal

--      GPIF, General Purpose Interface) and our FPGA. The interface is

--      synchronous, where the GPIF provides the clock. This FSM is synchronous

--      to the GPIF clock, also this side of the FIFO's.

--

--    You can find more detailed information how the interface works in the

--    ../Doc folder.

--

--  Target Devices:     general

--  Tool versions:      Xilinx ISE 11.1, XST

--  Dependencies:

--

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

library work;

use work.GECKO3COM_defines.all;

entity gpif_com_fsm is

  port (

    i_nReset        : in  std_logic;

    i_IFCLK         : in  std_logic;  -- GPIF CLK (GPIF is Master and provides the clock)

    i_WRU           : in  std_logic;    -- write from GPIF

    i_RDYU          : in  std_logic;    -- GPIF is ready

    i_U2X_FULL      : in  std_logic;

    i_U2X_AM_FULL   : in  std_logic;    -- signals for IN FIFO

    i_X2U_AM_EMPTY  : in  std_logic;

    i_X2U_EMPTY     : in  std_logic;    -- signals for OUT FIFO

    o_bus_trans_dir : out std_logic;

    o_U2X_WR_EN     : out std_logic;    -- signals for IN FIFO

    o_X2U_RD_EN     : out std_logic;    -- signals for OUT FIFO

    o_FIFOrst       : out std_logic;

    o_WRX           : out std_logic;    -- To write to GPIF

    o_RDYX          : out std_logic;    -- Core is ready

    o_ABORT         : out std_logic;  -- abort condition detected. we have to flush the data

    o_RX            : out std_logic;

    o_TX            : out std_logic     --

    );

  -- XST specific synthesize attributes

  attribute safe_implementation: string;

  attribute safe_recovery_state: string;

  attribute safe_implementation of gpif_com_fsm : entity is "yes";

end gpif_com_fsm;

architecture fsm of gpif_com_fsm is

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

  -- FSM

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

  type   t_busAccess is (readFromGPIF, writeToGPIF);

  signal s_bus_trans_dir : t_busAccess;

  type t_fsmState is (rst, idle,        -- controll states

                      inRQ, inACK, inTrans, inThrot,

                      inThrotEnd, endInTrans,  -- in com states

                      outRQ, outTrans, outWait, endOutTrans);  -- out com states

  signal pr_state, nx_state : t_fsmState;

  -- XST specific synthesize attributes

  attribute safe_recovery_state of pr_state : signal is "idle";

  attribute safe_recovery_state of nx_state : signal is "idle";

  -- interconection signals

  signal s_FIFOrst, s_RDYX, s_WRX, s_ABORT : std_logic;

  -- USB to Xilinx (U2X)

  signal s_U2X_WR_EN : std_logic;

  -- Xilinx to USB (X2U)

  signal s_X2U_RD_EN : std_logic;

begin

  o_FIFOrst       <= s_FIFOrst;

  o_X2U_RD_EN     <= s_X2U_RD_EN;

  o_WRX           <= s_WRX;

  o_RDYX          <= s_RDYX;

  o_U2X_WR_EN     <= s_U2X_WR_EN;

  o_bus_trans_dir <= '1' when s_bus_trans_dir = writeToGPIF else '0';

  o_ABORT         <= s_ABORT;

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

  -- FSM GPIF

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

  -- state reg

  action : process(i_IFCLK, i_nReset)

    variable v_setup : integer range 0 to 15;

  begin

    if i_nReset = '0' then

      pr_state <= rst;

    elsif rising_edge(i_IFCLK) then

        pr_state <= nx_state;

    end if;

  end process action;

  -- comb logic

  transaction : process(pr_state, i_WRU, i_RDYU, i_U2X_AM_FULL, i_X2U_EMPTY)

  begin  -- process transaction

    -- default signal values to avoid latches:

    s_FIFOrst       <= '0';

    s_bus_trans_dir <= readFromGPIF;

    s_U2X_WR_EN     <= '0';

    s_X2U_RD_EN     <= '0';

    nx_state        <= idle;

    s_WRX           <= '0';

    s_RDYX          <= '0';

    s_ABORT         <= '0';

    o_RX            <= '0';

    o_TX            <= '0';

    case pr_state is

      -- controll

      when rst =>

        -- output signal values:

        s_FIFOrst   <= '1';

        s_WRX       <= '0';

        s_RDYX      <= '0';

        s_U2X_WR_EN <= '0';

        s_X2U_RD_EN <= '0';

        s_ABORT     <= '1';

        o_RX        <= '0';

        o_TX        <= '0';

        s_bus_trans_dir <= readFromGPIF;

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state <= rst;

        else

          nx_state <= idle;

        end if;

      when idle =>

        -- output signal values:

        s_FIFOrst       <= '0';

        s_WRX           <= '0';

        s_RDYX          <= '0';

        s_U2X_WR_EN     <= '0';

        s_X2U_RD_EN     <= '0';

        s_bus_trans_dir <= readFromGPIF;

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state <= rst;

        elsif i_WRU = '1' and i_RDYU = '0' then

          nx_state <= inRQ;

        elsif i_WRU = '0' and i_X2U_EMPTY = '0' then

          nx_state <= outRQ;

        else

          nx_state <= idle;

        end if;

        -- in trans

      when inRQ =>

        -- output signal values:

        s_WRX  <= '0';

        s_RDYX <= '0';

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state <= rst;

        elsif i_U2X_FULL = '0' then

          nx_state <= inACK;

        else

          nx_state <= idle;

        end if;

      when inACK =>

        -- output signal values:

        s_WRX       <= '0';

        s_RDYX      <= '1';

        s_U2X_WR_EN <= '1';

        o_RX        <= '1';

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state <= rst;

        elsif i_WRU = '1' then

          nx_state <= inTrans;

          --nx_state <= inDummy;

        else

          nx_state <= endInTrans;

        end if;

      when inTrans =>

        -- output signal values:

        s_WRX       <= '0';

        s_RDYX      <= '1';

        s_U2X_WR_EN <= '1';

        o_RX        <= '1';

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state <= rst;

        elsif i_WRU = '0' then

          nx_state <= endInTrans;

        elsif i_U2X_FULL = '1' then

          nx_state <= inThrot;

        else

          nx_state <= inTrans;

        end if;

      when inThrot =>

        -- output signal values:

        s_WRX       <= '0';

        s_RDYX      <= '0';

        s_U2X_WR_EN <= '0';

        o_RX        <= '1';

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state <= rst;

        elsif i_U2X_FULL = '0' then

          --nx_state <= inThrotEnd;

          nx_state <= inACK;

        elsif i_WRU = '0' then

          nx_state <= endInTrans;

        else

          nx_state <= inThrot;

        end if;

      --when inThrotEnd =>

      --  -- this is a one clock delay to help the fx2 to see the RDYX signal.

      --  -- output signal values:

      --  s_WRX       <= '0';

      --  s_RDYX      <= '1';

      --  s_U2X_WR_EN <= '0';

      --  o_RX        <= '1';

      --  -- state decisions 

      --  nx_state <= inACK;

      when endInTrans =>

        -- output signal values:

        s_WRX       <= '0';

        s_RDYX      <= '0';

        s_U2X_WR_EN <= '1';

        -- state decisions

        nx_state <= idle;

        -- out trans

      when outRQ =>

        -- output signal values:

        s_WRX  <= '1';

        s_RDYX <= '0';

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state <= rst;

        elsif i_WRU = '1' and i_RDYU = '0' then

          nx_state <= inRQ;

        elsif i_WRU = '0' and i_RDYU = '0' then  -- vervollständigt, wenn ez-usb noch beschäfigt mit altem transfer

          --s_X2U_RD_EN <= '1';

          nx_state    <= outTrans;

--            s_bus_trans_dir <= writeToGPIF;

        else

          nx_state <= outRQ;

        end if;

      when outTrans =>

        -- output signal values:

        s_WRX           <= '1';

        s_RDYX          <= '0';

        s_X2U_RD_EN     <= '1';

        s_bus_trans_dir <= writeToGPIF;

        o_TX            <= '1';

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state        <= rst;

        elsif i_X2U_EMPTY = '1' then

          nx_state <= endOutTrans;

        elsif i_WRU = '0' and i_RDYU = '1' then

          nx_state <= outTrans;

        else

          --s_X2U_RD_EN <= '0';           -- to realise a wait case

          nx_state    <= outWait;

        end if;

      when outWait =>

        -- output signal values:

        s_WRX       <= '1';

        s_RDYX      <= '0';

        s_X2U_RD_EN <= '0';

        o_TX        <= '1';

        s_bus_trans_dir <= writeToGPIF;

        -- state decisions

        if i_WRU = '1' and i_RDYU = '1' then

          nx_state <= rst;

        elsif i_WRU = '0' and i_RDYU = '1' then

          nx_state <= outTrans;

        else

          nx_state <= outWait;

        end if;

      when endOutTrans =>

        -- output signal values:

        s_RDYX          <= '0';

        s_WRX           <= '1';  -- nötig um letzte 16bit an ez-usb zu schreiben

        s_X2U_RD_EN     <= '1';  -- nötig da empyte flag schon beim ersten fifo zugriff auftaucht, zweite 16bit müssen noch gelesen werden

        s_bus_trans_dir <= writeToGPIF;

        -- state decisions

        nx_state        <= idle;

        -- error case

      when others =>

        nx_state <= idle;

    end case;

  end process transaction;

end fsm;