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--

--      fifo.vhd

--

--      simple fifo

--

--      uses FF and every rd or wr has to 'bubble' through the hole fifo.

--      

--      Author: Martin Schoeberl        martin.schoeberl@chello.at

--

--

--      resources on ACEX1K

--

--              (width+2)*depth-1 LCs

--

--

--      2002-01-06      first working version

--      2002-11-03      a signal for reaching threshold

--      2005-02-20      change entity order for modelsim vcom

--

library ieee;

use ieee.std_logic_1164.all;

entity fifo_elem is

generic (width : integer);

port (

        clk             : in std_logic;

        reset   : in std_logic;

        din             : in std_logic_vector(width-1 downto 0);

        dout    : out std_logic_vector(width-1 downto 0);

        rd              : in std_logic;

        wr              : in std_logic;

        rd_prev : out std_logic;

        full    : out std_logic

);

end fifo_elem;

architecture rtl of fifo_elem is

        signal buf              : std_logic_vector(width-1 downto 0);

        signal f                : std_logic;

begin

        dout <= buf;

process(clk, reset, f)

begin

        full <= f;

        if (reset='0') then

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

                f <= '0';

                rd_prev <= '0';

        elsif rising_edge(clk) then

                rd_prev <= '0';

                if f='0' then

                        if wr='1' then

                                rd_prev <= '1';

                                buf <= din;

                                f <= '1';

                        end if;

                else

                        if rd='1' then

                                f <= '0';

                        end if;

                end if;

        end if;

end process;

end rtl;

library ieee;

use ieee.std_logic_1164.all;

entity fifo is

generic (width : integer := 8; depth : integer := 4; thres : integer := 2);

port (

        clk             : in std_logic;

        reset   : in std_logic;

        din             : in std_logic_vector(width-1 downto 0);

        dout    : out std_logic_vector(width-1 downto 0);

        rd              : in std_logic;

        wr              : in std_logic;

        empty   : out std_logic;

        full    : out std_logic;

        half    : out std_logic

);

end fifo ;

architecture rtl of fifo is

component fifo_elem is

generic (width : integer);

port (

        clk             : in std_logic;

        reset   : in std_logic;

        din             : in std_logic_vector(width-1 downto 0);

        dout    : out std_logic_vector(width-1 downto 0);

        rd              : in std_logic;

        wr              : in std_logic;

        rd_prev : out std_logic;

        full    : out std_logic

);

end component;

        signal r, w, rp, f      : std_logic_vector(depth-1 downto 0);

        type d_array is array (0 to depth-1) of std_logic_vector(width-1 downto 0);

        signal di, do           : d_array;

begin

        g1: for i in 0 to depth-1 generate

                f1: fifo_elem generic map (width)

                        port map (clk, reset, di(i), do(i), r(i), w(i), rp(i), f(i));

                x: if i<depth-1 generate

                        r(i) <= rp(i+1);

                        w(i+1) <= f(i);

                        di(i+1) <= do(i);

                end generate;

        end generate;

        di(0) <= din;

        dout <= do(depth-1);

        w(0) <= wr;

        r(depth-1) <= rd;

        full <= f(0);

        half <= f(depth-thres);

        empty <= not f(depth-1);

end rtl;