Subversion Repositories rio

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

-- 

-- RapidIO IP Library Core

-- 

-- This file is part of the RapidIO IP library project

-- http://www.opencores.org/cores/rio/

-- 

-- Description

-- Containing RapidIO packet buffering functionallity. Two different entities

-- are implemented, one with transmission window support and one without.

-- 

-- To Do:

-- -

-- 

-- Author(s): 

-- - Magnus Rosenius, magro732@opencores.org 

-- 

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

-- 

-- Copyright (C) 2013 Authors and OPENCORES.ORG 

-- 

-- This source file may be used and distributed without 

-- restriction provided that this copyright statement is not 

-- removed from the file and that any derivative work contains 

-- the original copyright notice and the associated disclaimer. 

-- 

-- This source file is free software; you can redistribute it 

-- and/or modify it under the terms of the GNU Lesser General 

-- Public License as published by the Free Software Foundation; 

-- either version 2.1 of the License, or (at your option) any 

-- later version. 

-- 

-- This source 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 Lesser General Public License for more 

-- details. 

-- 

-- You should have received a copy of the GNU Lesser General 

-- Public License along with this source; if not, download it 

-- from http://www.opencores.org/lgpl.shtml 

-- 

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

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

-- RioPacketBuffer

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.rio_common.all;

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

-- Entity for RioPacketBuffer.

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

entity RioPacketBuffer is

  generic(

    SIZE_ADDRESS_WIDTH : natural := 6;

    CONTENT_ADDRESS_WIDTH : natural := 8);

  port(

    clk : in std_logic;

    areset_n : in std_logic;

    inboundWriteFrameFull_o : out std_logic;

    inboundWriteFrame_i : in std_logic;

    inboundWriteFrameAbort_i : in std_logic;

    inboundWriteContent_i : in std_logic;

    inboundWriteContentData_i : in std_logic_vector(31 downto 0);

    inboundReadFrameEmpty_o : out std_logic;

    inboundReadFrame_i : in std_logic;

    inboundReadFrameRestart_i : in std_logic;

    inboundReadFrameAborted_o : out std_logic;

    inboundReadContentEmpty_o : out std_logic;

    inboundReadContent_i : in std_logic;

    inboundReadContentEnd_o : out std_logic;

    inboundReadContentData_o : out std_logic_vector(31 downto 0);

    outboundWriteFrameFull_o : out std_logic;

    outboundWriteFrame_i : in std_logic;

    outboundWriteFrameAbort_i : in std_logic;

    outboundWriteContent_i : in std_logic;

    outboundWriteContentData_i : in std_logic_vector(31 downto 0);

    outboundReadFrameEmpty_o : out std_logic;

    outboundReadFrame_i : in std_logic;

    outboundReadFrameRestart_i : in std_logic;

    outboundReadFrameAborted_o : out std_logic;

    outboundReadContentEmpty_o : out std_logic;

    outboundReadContent_i : in std_logic;

    outboundReadContentEnd_o : out std_logic;

    outboundReadContentData_o : out std_logic_vector(31 downto 0));

end entity;

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

-- Architecture for RioPacketBuffer.

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

architecture RioPacketBufferImpl of RioPacketBuffer is

  component PacketBufferContinous is

    generic(

      SIZE_ADDRESS_WIDTH : natural;

      CONTENT_ADDRESS_WIDTH : natural);

    port(

      clk : in std_logic;

      areset_n : in std_logic;

      writeFrameFull_o : out std_logic;

      writeFrame_i : in std_logic;

      writeFrameAbort_i : in std_logic;

      writeContent_i : in std_logic;

      writeContentData_i : in std_logic_vector(31 downto 0);

      readFrameEmpty_o : out std_logic;

      readFrame_i : in std_logic;

      readFrameRestart_i : in std_logic;

      readFrameAborted_o : out std_logic;

      readContentEmpty_o : out std_logic;

      readContent_i : in std_logic;

      readContentEnd_o : out std_logic;

      readContentData_o : out std_logic_vector(31 downto 0));

  end component;

begin

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

  -- Outbound frame buffers.

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

  OutboundPacketBuffer: PacketBufferContinous

    generic map(

      SIZE_ADDRESS_WIDTH=>SIZE_ADDRESS_WIDTH,

      CONTENT_ADDRESS_WIDTH=>CONTENT_ADDRESS_WIDTH)

    port map(

      clk=>clk,

      areset_n=>areset_n,

      writeFrameFull_o=>outboundWriteFrameFull_o,

      writeFrame_i=>outboundWriteFrame_i, writeFrameAbort_i=>outboundWriteFrameAbort_i,

      writeContent_i=>outboundWriteContent_i, writeContentData_i=>outboundWriteContentData_i,

      readFrameEmpty_o=>outboundReadFrameEmpty_o,

      readFrame_i=>outboundReadFrame_i, readFrameRestart_i=>outboundReadFrameRestart_i,

      readFrameAborted_o=>outboundReadFrameAborted_o,

      readContentEmpty_o=>outboundReadContentEmpty_o,

      readContent_i=>outboundReadContent_i, readContentEnd_o=>outboundReadContentEnd_o,

      readContentData_o=>outboundReadContentData_o);

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

  -- Inbound frame buffers.

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

  InboundPacketBuffer: PacketBufferContinous

    generic map(

      SIZE_ADDRESS_WIDTH=>SIZE_ADDRESS_WIDTH,

      CONTENT_ADDRESS_WIDTH=>CONTENT_ADDRESS_WIDTH)

    port map(

      clk=>clk,

      areset_n=>areset_n,

      writeFrameFull_o=>inboundWriteFrameFull_o,

      writeFrame_i=>inboundWriteFrame_i, writeFrameAbort_i=>inboundWriteFrameAbort_i,

      writeContent_i=>inboundWriteContent_i, writeContentData_i=>inboundWriteContentData_i,

      readFrameEmpty_o=>inboundReadFrameEmpty_o,

      readFrame_i=>inboundReadFrame_i, readFrameRestart_i=>inboundReadFrameRestart_i,

      readFrameAborted_o=>inboundReadFrameAborted_o,

      readContentEmpty_o=>inboundReadContentEmpty_o,

      readContent_i=>inboundReadContent_i, readContentEnd_o=>inboundReadContentEnd_o,

      readContentData_o=>inboundReadContentData_o);

end architecture;

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

-- RioPacketBufferWindow

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.rio_common.all;

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

-- Entity for RioPacketBufferWindow.

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

entity RioPacketBufferWindow is

  generic(

    SIZE_ADDRESS_WIDTH : natural := 6;

    CONTENT_ADDRESS_WIDTH : natural := 8);

  port(

    clk : in std_logic;

    areset_n : in std_logic;

    inboundWriteFrameFull_o : out std_logic;

    inboundWriteFrame_i : in std_logic;

    inboundWriteFrameAbort_i : in std_logic;

    inboundWriteContent_i : in std_logic;

    inboundWriteContentData_i : in std_logic_vector(31 downto 0);

    inboundReadFrameEmpty_o : out std_logic;

    inboundReadFrame_i : in std_logic;

    inboundReadFrameRestart_i : in std_logic;

    inboundReadFrameAborted_o : out std_logic;

    inboundReadContentEmpty_o : out std_logic;

    inboundReadContent_i : in std_logic;

    inboundReadContentEnd_o : out std_logic;

    inboundReadContentData_o : out std_logic_vector(31 downto 0);

    outboundWriteFrameFull_o : out std_logic;

    outboundWriteFrame_i : in std_logic;

    outboundWriteFrameAbort_i : in std_logic;

    outboundWriteContent_i : in std_logic;

    outboundWriteContentData_i : in std_logic_vector(31 downto 0);

    outboundReadFrameEmpty_o : out std_logic;

    outboundReadFrame_i : in std_logic;

    outboundReadFrameRestart_i : in std_logic;

    outboundReadFrameAborted_o : out std_logic;

    outboundReadWindowEmpty_o : out std_logic;

    outboundReadWindowReset_i : in std_logic;

    outboundReadWindowNext_i : in std_logic;

    outboundReadContentEmpty_o : out std_logic;

    outboundReadContent_i : in std_logic;

    outboundReadContentEnd_o : out std_logic;

    outboundReadContentData_o : out std_logic_vector(31 downto 0));

end entity;

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

-- Architecture for RioPacketBufferWindow.

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

architecture RioPacketBufferWindowImpl of RioPacketBufferWindow is

  component PacketBufferContinous is

    generic(

      SIZE_ADDRESS_WIDTH : natural;

      CONTENT_ADDRESS_WIDTH : natural);

    port(

      clk : in std_logic;

      areset_n : in std_logic;

      writeFrameFull_o : out std_logic;

      writeFrame_i : in std_logic;

      writeFrameAbort_i : in std_logic;

      writeContent_i : in std_logic;

      writeContentData_i : in std_logic_vector(31 downto 0);

      readFrameEmpty_o : out std_logic;

      readFrame_i : in std_logic;

      readFrameRestart_i : in std_logic;

      readFrameAborted_o : out std_logic;

      readContentEmpty_o : out std_logic;

      readContent_i : in std_logic;

      readContentEnd_o : out std_logic;

      readContentData_o : out std_logic_vector(31 downto 0));

  end component;

  component PacketBufferContinousWindow is

    generic(

      SIZE_ADDRESS_WIDTH : natural;

      CONTENT_ADDRESS_WIDTH : natural);

    port(

      clk : in std_logic;

      areset_n : in std_logic;

      writeFrameFull_o : out std_logic;

      writeFrame_i : in std_logic;

      writeFrameAbort_i : in std_logic;

      writeContent_i : in std_logic;

      writeContentData_i : in std_logic_vector(31 downto 0);

      readFrameEmpty_o : out std_logic;

      readFrame_i : in std_logic;

      readFrameRestart_i : in std_logic;

      readFrameAborted_o : out std_logic;

      readWindowEmpty_o : out std_logic;

      readWindowReset_i : in std_logic;

      readWindowNext_i : in std_logic;

      readContentEmpty_o : out std_logic;

      readContent_i : in std_logic;

      readContentEnd_o : out std_logic;

      readContentData_o : out std_logic_vector(31 downto 0));

  end component;

begin

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

  -- Outbound frame buffers.

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

  OutboundPacketBuffer: PacketBufferContinousWindow

    generic map(

      SIZE_ADDRESS_WIDTH=>SIZE_ADDRESS_WIDTH,

      CONTENT_ADDRESS_WIDTH=>CONTENT_ADDRESS_WIDTH)

    port map(

      clk=>clk,

      areset_n=>areset_n,

      writeFrameFull_o=>outboundWriteFrameFull_o,

      writeFrame_i=>outboundWriteFrame_i, writeFrameAbort_i=>outboundWriteFrameAbort_i,

      writeContent_i=>outboundWriteContent_i, writeContentData_i=>outboundWriteContentData_i,

      readFrameEmpty_o=>outboundReadFrameEmpty_o,

      readFrame_i=>outboundReadFrame_i, readFrameRestart_i=>outboundReadFrameRestart_i,

      readFrameAborted_o=>outboundReadFrameAborted_o,

      readWindowEmpty_o=>outboundReadWindowEmpty_o,

      readWindowReset_i=>outboundReadWindowReset_i,

      readWindowNext_i=>outboundReadWindowNext_i,

      readContentEmpty_o=>outboundReadContentEmpty_o,

      readContent_i=>outboundReadContent_i, readContentEnd_o=>outboundReadContentEnd_o,

      readContentData_o=>outboundReadContentData_o);

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

  -- Inbound frame buffers.

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

  InboundPacketBuffer: PacketBufferContinous

    generic map(

      SIZE_ADDRESS_WIDTH=>SIZE_ADDRESS_WIDTH,

      CONTENT_ADDRESS_WIDTH=>CONTENT_ADDRESS_WIDTH)

    port map(

      clk=>clk,

      areset_n=>areset_n,

      writeFrameFull_o=>inboundWriteFrameFull_o,

      writeFrame_i=>inboundWriteFrame_i, writeFrameAbort_i=>inboundWriteFrameAbort_i,

      writeContent_i=>inboundWriteContent_i, writeContentData_i=>inboundWriteContentData_i,

      readFrameEmpty_o=>inboundReadFrameEmpty_o,

      readFrame_i=>inboundReadFrame_i, readFrameRestart_i=>inboundReadFrameRestart_i,

      readFrameAborted_o=>inboundReadFrameAborted_o,

      readContentEmpty_o=>inboundReadContentEmpty_o,

      readContent_i=>inboundReadContent_i, readContentEnd_o=>inboundReadContentEnd_o,

      readContentData_o=>inboundReadContentData_o);

end architecture;

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

-- PacketBufferContinous

-- This component stores data in chuncks and stores the size of them. The full

-- memory can be used, except for one word, or a specified (using generic)

-- maximum number of frames.

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

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

-- Entity for PacketBufferContinous.

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

entity PacketBufferContinous is

  generic(

    SIZE_ADDRESS_WIDTH : natural;

    CONTENT_ADDRESS_WIDTH : natural);

  port(

    clk : in std_logic;

    areset_n : in std_logic;

    writeFrameFull_o : out std_logic;

    writeFrame_i : in std_logic;

    writeFrameAbort_i : in std_logic;

    writeContent_i : in std_logic;

    writeContentData_i : in std_logic_vector(31 downto 0);

    readFrameEmpty_o : out std_logic;

    readFrame_i : in std_logic;

    readFrameRestart_i : in std_logic;

    readFrameAborted_o : out std_logic;

    readContentEmpty_o : out std_logic;

    readContent_i : in std_logic;

    readContentEnd_o : out std_logic;

    readContentData_o : out std_logic_vector(31 downto 0));

end entity;

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

-- Architecture for PacketBufferContinous.

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

architecture PacketBufferContinousImpl of PacketBufferContinous is

  component MemorySimpleDualPortAsync is

    generic(

      ADDRESS_WIDTH : natural := 1;

      DATA_WIDTH : natural := 1);

    port(

      clkA_i : in std_logic;

      enableA_i : in std_logic;

      addressA_i : in std_logic_vector(ADDRESS_WIDTH-1 downto 0);

      dataA_i : in std_logic_vector(DATA_WIDTH-1 downto 0);

      addressB_i : in std_logic_vector(ADDRESS_WIDTH-1 downto 0);

      dataB_o : out std_logic_vector(DATA_WIDTH-1 downto 0));

  end component;

  component MemorySimpleDualPort is

    generic(

      ADDRESS_WIDTH : natural := 1;

      DATA_WIDTH : natural := 1);

    port(

      clkA_i : in std_logic;

      enableA_i : in std_logic;

      addressA_i : in std_logic_vector(ADDRESS_WIDTH-1 downto 0);

      dataA_i : in std_logic_vector(DATA_WIDTH-1 downto 0);

      clkB_i : in std_logic;

      enableB_i : in std_logic;

      addressB_i : in std_logic_vector(ADDRESS_WIDTH-1 downto 0);

      dataB_o : out std_logic_vector(DATA_WIDTH-1 downto 0));

  end component;

  -- The number of available word positions left in the memory.

  signal available : unsigned(CONTENT_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  -- The position to place new frames.

  signal backIndex, backIndexNext : unsigned(SIZE_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  -- The position to remove old frames.

  signal frontIndex, frontIndexNext : unsigned(SIZE_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  -- The size of the current frame.

  signal readFrameEnd_p : unsigned(CONTENT_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  -- The start of unread content.

  signal memoryStart_p : unsigned(CONTENT_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  -- The current reading position.

  signal memoryRead_p, memoryReadNext_p : unsigned(CONTENT_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  -- The end of unread content.

  signal memoryEnd_p : unsigned(CONTENT_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  -- The current writing position.

  signal memoryWrite_p, memoryWriteNext_p : unsigned(CONTENT_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  -- Memory output signal containing the position of a frame.

  signal framePositionReadData : std_logic_vector(CONTENT_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

begin

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

  -- Internal signal assignments.

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

  available <= not (memoryEnd_p - memoryStart_p);

  backIndexNext <= backIndex + 1;

  frontIndexNext <= frontIndex + 1;

  memoryWriteNext_p <= memoryWrite_p + 1;

  memoryReadNext_p <= memoryRead_p + 1;

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

  -- Writer logic.

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

  writeFrameFull_o <= '1' when ((backIndexNext = frontIndex) or

                                (available <= 68)) else '0';

  Writer: process(clk, areset_n)

  begin

    if (areset_n = '0') then

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

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

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

    elsif (clk'event and clk = '1') then

      if (writeFrameAbort_i = '1') then

        memoryWrite_p <= memoryEnd_p;

      elsif (writeContent_i = '1') then

        memoryWrite_p <= memoryWriteNext_p;

      end if;

      if(writeFrame_i = '1') then

        memoryEnd_p <= memoryWrite_p;

        backIndex <= backIndexNext;

      end if;

    end if;

  end process;

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

  -- Frame cancellation logic.

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

  process(clk, areset_n)

  begin

    if (areset_n = '0') then

      readFrameAborted_o <= '0';

    elsif (clk'event and clk = '1') then

      if ((frontIndex = backIndex) and

          ((writeFrameAbort_i = '1') and (readFrameRestart_i = '0'))) then

        readFrameAborted_o <= '1';

      elsif ((writeFrameAbort_i = '0') and (readFrameRestart_i = '1')) then

        readFrameAborted_o <= '0';

      end if;

    end if;

  end process;

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

  -- Reader logic.

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

  readFrameEmpty_o <= '1' when (frontIndex = backIndex) else '0';

  readContentEmpty_o <= '1' when ((frontIndex = backIndex) and

                                  (memoryWrite_p = memoryRead_p)) else '0';

  Reader: process(clk, areset_n)

  begin

    if (areset_n = '0') then

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

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

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

      readContentEnd_o <= '0';

    elsif (clk'event and clk = '1') then

      -- REMARK: Break apart into registers to avoid priority ladder???

      if(readFrameRestart_i = '1') then

        memoryRead_p <= memoryStart_p;

      elsif(readContent_i = '1') then

        if(memoryRead_p = readFrameEnd_p) then

          readContentEnd_o <= '1';

        else

          readContentEnd_o <= '0';

          memoryRead_p <= memoryReadNext_p;

        end if;

      elsif(readFrame_i = '1') then

        memoryStart_p <= readFrameEnd_p;

        frontIndex <= frontIndexNext;

        memoryRead_p <= readFrameEnd_p;

      end if;

    end if;

  end process;

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

  -- Frame positioning memory signals.

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

  readFrameEnd_p <= unsigned(framePositionReadData);

  -- Memory to keep frame starting/ending positions in.

  FramePosition: MemorySimpleDualPortAsync

    generic map(ADDRESS_WIDTH=>SIZE_ADDRESS_WIDTH, DATA_WIDTH=>CONTENT_ADDRESS_WIDTH)

    port map(

      clkA_i=>clk, enableA_i=>writeFrame_i,

      addressA_i=>std_logic_vector(backIndex), dataA_i=>std_logic_vector(memoryWrite_p),

      addressB_i=>std_logic_vector(frontIndex), dataB_o=>framePositionReadData);

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

  -- Frame content memory signals.

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

  -- Memory to keep frame content in.

  -- REMARK: Use paritybits here as well to make sure the frame data does not

  -- become corrupt???

  FrameContent: MemorySimpleDualPort

    generic map(ADDRESS_WIDTH=>CONTENT_ADDRESS_WIDTH, DATA_WIDTH=>32)

    port map(

      clkA_i=>clk, enableA_i=>writeContent_i,

      addressA_i=>std_logic_vector(memoryWrite_p), dataA_i=>writeContentData_i,

      clkB_i=>clk, enableB_i=>readContent_i,

      addressB_i=>std_logic_vector(memoryRead_p), dataB_o=>readContentData_o);

end architecture;

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

-- PacketBufferContinousWindow

-- This component stores data in chuncks and stores the size of them. The full

-- memory can be used, except for one word, or a specified (using generic)

-- maximum number of frames.

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

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

-- Entity for PacketBufferContinousWindow.

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

entity PacketBufferContinousWindow is

  generic(

    SIZE_ADDRESS_WIDTH : natural;

    CONTENT_ADDRESS_WIDTH : natural);

  port(

    clk : in std_logic;

    areset_n : in std_logic;

    writeFrameFull_o : out std_logic;

    writeFrame_i : in std_logic;

    writeFrameAbort_i : in std_logic;

    writeContent_i : in std_logic;

    writeContentData_i : in std_logic_vector(31 downto 0);

    readFrameEmpty_o : out std_logic;

    readFrame_i : in std_logic;

    readFrameRestart_i : in std_logic;

    readFrameAborted_o : out std_logic;

    readWindowEmpty_o : out std_logic;

    readWindowReset_i : in std_logic;

    readWindowNext_i : in std_logic;

    readContentEmpty_o : out std_logic;

    readContent_i : in std_logic;

    readContentEnd_o : out std_logic;

    readContentData_o : out std_logic_vector(31 downto 0));

end entity;

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

-- Architecture for PacketBufferContinousWindow.

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

architecture PacketBufferContinousWindowImpl of PacketBufferContinousWindow is

  component MemorySimpleDualPortAsync is

    generic(

      ADDRESS_WIDTH : natural := 1;

      DATA_WIDTH : natural := 1);

    port(

      clkA_i : in std_logic;

      enableA_i : in std_logic;

      addressA_i : in std_logic_vector(ADDRESS_WIDTH-1 downto 0);

      dataA_i : in std_logic_vector(DATA_WIDTH-1 downto 0);

      addressB_i : in std_logic_vector(ADDRESS_WIDTH-1 downto 0);

      dataB_o : out std_logic_vector(DATA_WIDTH-1 downto 0));

  end component;

  component MemorySimpleDualPort is

    generic(

      ADDRESS_WIDTH : natural := 1;

      DATA_WIDTH : natural := 1);

    port(

      clkA_i : in std_logic;

      enableA_i : in std_logic;

      addressA_i : in std_logic_vector(ADDRESS_WIDTH-1 downto 0);

      dataA_i : in std_logic_vector(DATA_WIDTH-1 downto 0);

      clkB_i : in std_logic;

      enableB_i : in std_logic;

      addressB_i : in std_logic_vector(ADDRESS_WIDTH-1 downto 0);

      dataB_o : out std_logic_vector(DATA_WIDTH-1 downto 0));

  end component;

  -- The number of available word positions left in the memory.

  signal available : unsigned(CONTENT_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  signal backIndex, backIndexNext : unsigned(SIZE_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  signal frontIndex, frontIndexNext : unsigned(SIZE_ADDRESS_WIDTH-1 downto 0) := (others=>'0');

  signal windowIndex, windowIndexNext : unsigned(SIZE_ADDRESS_WIDTH-1 downto 0) := (others=>'0');