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

--  This file is a part of the GRLIB VHDL IP LIBRARY

--  Copyright (C) 2003, Gaisler Research

--

--  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 2 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, write to the Free Software

--  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 

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

-- Entity:      atahost_dma_fifo

-- File:        atahost_dma_fifo.vhd

-- Author:      Erik Jagre - Gaisler Research

-- Description: Generic FIFO, based on syncram in grlib

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

library IEEE;

use IEEE.std_logic_1164.all;

use ieee.std_logic_arith.all;

library techmap;

use techmap.gencomp.all;

entity atahost_dma_fifo is

  generic(tech  : integer:=0;  abits : integer:=3;

          dbits : integer:=32; depth : integer:=8);

  port( clk          : in std_logic;

        reset        : in std_logic;

        write_enable : in std_logic;

        read_enable  : in std_logic;

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

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

        write_error  : out std_logic:='0';

        read_error   : out std_logic:='0';

        level        : out natural range 0 to depth;

        empty        : out std_logic:='1';

        full         : out std_logic:='0');

end;

architecture rtl of atahost_dma_fifo is

type state_type is (full_state, empty_state, idle_state);

type reg_type is record

  state      : state_type;

  level      : integer range 0 to depth;

  aw         : integer range 0 to depth;

  ar         : integer range 0 to depth;

  data_o     : std_logic_vector(dbits-1 downto 0);

  rd         : std_logic;

  wr         : std_logic;

  erd        : std_logic;

  ewr        : std_logic;

  reset      : std_logic;

  adr        : std_logic_vector(abits-1 downto 0);

end record;

constant RESET_VECTOR : reg_type := (empty_state,0,0,0,

  conv_std_logic_vector(0,dbits),'0','0','0','0','0',(others=>'0'));

signal r,ri : reg_type;

signal s_ram_adr : std_logic_vector(abits-1 downto 0);

begin

--  comb:process(write_enable, read_enable, data_in,reset, r) Erik 2007-02-08

  comb:process(write_enable, read_enable, reset, r)

  variable v : reg_type;

  variable vfull, vempty : std_logic;

  begin

    v:=r;

    v.wr:=write_enable; v.rd:=read_enable; v.reset:=reset;

    case r.state is

      when full_state=>

        if write_enable='1' and read_enable='0' and reset='0' then

          v.ewr:='1'; v.state:=full_state;

        elsif write_enable='0' and read_enable='1' and reset='0' then

          v.adr:=conv_std_logic_vector(r.ar,abits);

          if r.ar=depth-1 then v.ar:=0; else v.ar:=r.ar+1; end if;

          v.level:=r.level-1;

          if r.aw=v.ar then v.state:=empty_state;

          else v.state:=idle_state; end if;

          v.ewr:='0';

        end if;

      when empty_state=>

        if write_enable='1' and read_enable='0' and reset='0' then

          v.adr:=conv_std_logic_vector(r.aw,abits);

          if r.aw=depth-1 then v.aw:=0; else v.aw:=r.aw+1; end if;

          v.level:=r.level+1;

          if v.aw=r.ar then v.state:=full_state;

          else v.state:=idle_state; end if;

          v.erd:='0';

        elsif write_enable='0' and read_enable='1' and reset='0' then

          v.erd:='1'; v.state:=empty_state;

        end if;

      when idle_state=>

        if write_enable='1' and read_enable='0' and reset='0' then

          v.adr:=conv_std_logic_vector(r.aw,abits);

          if r.aw=depth-1 then v.aw:=0; else v.aw:=r.aw+1; end if;

          v.level:=r.level+1;

          if v.level=depth then v.state:=full_state;

          else v.state:=idle_state; end if;

        elsif write_enable='0' and read_enable='1' and reset='0' then

          v.adr:=conv_std_logic_vector(r.ar,abits);

          if r.ar=depth-1 then v.ar:=0; else v.ar:=r.ar+1; end if;

          v.level:=r.level-1;

          if v.level=0 then v.state:=empty_state;

          else v.state:=idle_state; end if;

        end if;

    end case;

    if r.level=0 then vempty:='1'; vfull:='0';

    elsif r.level=depth then vempty:='0'; vfull:='1';

    else vempty:='0'; vfull:='0'; end if;

    --reset logic

    if (reset='1') then v:=RESET_VECTOR; end if;

    ri<=v;

    s_ram_adr<=v.adr;

    --assigning outport

    write_error<=v.ewr; read_error<=v.erd; level<=v.level;

    empty<=vempty; full<=vfull;

  end process;

  ram : syncram

  generic map(tech=>tech, abits=>abits, dbits=>dbits)

  port map (

    clk     => clk,

    address => s_ram_adr,

    datain  => data_in,

    dataout => data_out,

    enable  => read_enable,

    write   => write_enable

  );

  sync:process(clk)     --Activate on clock & reset

  begin

    if clk'event and clk='1' then r<=ri; end if;

  end process;

end;