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

-- File :       addr_data_demux_read.vdh

-- Description: Reads addr and data sequentially and outputs them in parallel.

--              Can be used, e.g., in interfacing HIBI with IP.

--

-- Project:

-- Author:     Erno Salminen

-- Date :      2003

-- Modified:

-- 06.08.2004   ES, one_data_in/out removed

--

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

-- Funbase IP library Copyright (C) 2011 TUT Department of Computer Systems

--

-- This file is part of HIBI

--

-- 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

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

entity addr_data_demux_read is

  generic (

    data_width_g : integer := 0;

    addr_width_g : integer := 0;

    comm_width_g : integer := 0

    );

  port (

    clk   : in std_logic;

    rst_n : in std_logic;

    av_in    : in  std_logic;

    data_in  : in  std_logic_vector (data_width_g-1 downto 0);

    comm_in  : in  std_logic_vector (comm_width_g-1 downto 0);

    empty_in : in  std_logic;

    re_out   : out std_logic;

    re_in     : in  std_logic;

    addr_out  : out std_logic_vector (addr_width_g-1 downto 0);

    data_out  : out std_logic_vector (data_width_g-1 downto 0);

    comm_out  : out std_logic_vector (comm_width_g-1 downto 0);

    empty_out : out std_logic

    );

end addr_data_demux_read;

architecture rtl of addr_data_demux_read is

  signal addr_r   : std_logic_vector (addr_width_g-1 downto 0);

  signal re_r     : std_logic;

  signal rd_rdy_r : std_logic;

begin  -- rtl

  -- 1) COMB PROC

  Read_fifo : process (re_in, re_r, empty_in, av_in)

  begin  -- process Read_fifo

    -- 21.01.2003 kokeilukorjaus, saa nähdä toimiiko jos IP pitää koko ajan re=1

    if empty_in = '1' then

      -- Fifossa ei ole mitaan

      re_out <= '0';

    else

      if av_in = '1' then

        -- Demux reads addr

        re_out <= re_r;

      else

        -- IP reads data

        re_out <= re_in;

      end if;

    end if;

  end process Read_fifo;

  -- 2) COMB PROC

  Assign_empty_out : process (empty_in, av_in)

  begin  -- process Assign_empty_out

    -- addr must read to register before it is tramsferred to reader.

    -- Therefore, empty_out is asserted until addr is read from fifo. 

    if empty_in = '1' then

      -- Fifossa ei ole mitaan

      empty_out <= '1';

    else

      if av_in = '1' then

        empty_out <= '1';

      else

        empty_out <= '0';

      end if;

    end if;

  end process Assign_empty_out;

  -- 3) COMB PROC

  Demux_addr_data : process (data_in, av_in, comm_in,

                             addr_r, empty_in)

  begin  -- process Demux_addr_data

    -- Fifo outputs are directed outputs when addr has been read to register

    -- and there is data coming from fifo

    if empty_in = '0' and av_in = '0' then

      -- data coming from fifo

      data_out <= data_in;

      addr_out <= addr_r;

      comm_out <= comm_in;

    else

      -- addr coming fifo or fifo empty 

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

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

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

    end if;

  end process Demux_addr_data;

  -- 4) SEQ PROC

  Store_addr : process (clk, rst_n)

  begin  -- process Store_addr

    -- Reads addr from fifo to register

    -- read_ready goes 1 after each fifo read operation, either initiated

    --  + by demux (=addr read). 

    --  + by reader ip (=data read).

    -- read_ready remains 1, if fifo became empty

    --  

    --  Read goes 0 if fifo is not empty and no read operation is performed,

    --  see above.

    if rst_n = '0' then                 -- asynchronous reset (active low)

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

      re_r     <= '0';

      rd_rdy_r <= '1';

    elsif clk'event and clk = '1' then  -- rising clock edge

      if empty_in = '1' then

        -- Fifo is empty, keep state

        addr_r   <= addr_r;

        re_r     <= '0';

        rd_rdy_r <= rd_rdy_r;

      else

        -- Fifo not empty

        if av_in = '1' then

          -- Fifo has addr, read it

          addr_r <= data_in(addr_width_g-1 downto 0);

          -- Keep RE=1 for one cycle

          if re_r = '0' then

            re_r     <= '1';

            rd_rdy_r <= '0';

          else

            re_r     <= '0';

            rd_rdy_r <= '1';

          end if;  --re_r

          --assert false report "New addr in fifo" severity note;

        else

          -- Fifossa on lukematon data

          addr_r <= addr_r;

          re_r   <= '0';

          if re_in = '1' then

            -- Reader ip perfroms read operation

            rd_rdy_r <= '1';

            --assert false report "IP reads addr+data" severity note;

          else

            -- Wait, until read ip performs read operation

            rd_rdy_r <= '0';

            --assert false report "Wait for IP to read addr+data" severity note;            

          end if;  --re_in

        end if;  --av        

      end if;  --empty_in

    end if;  --rst_n    

  end process Store_addr;

end rtl;  --addr_data_demux_read