source: PROJECT_CORE_MPI/SWITCH_GEN/TRUNK/FIFO_DP.vhd

----------------------------------------------------------------------------------
-- Company: 
-- Engineer: 
-- 
-- Create Date:    16:32:59 10/23/2012 
-- Design Name: 
-- Module Name:    FIFO_DP - Behavioral 
-- Project Name: 
-- Target Devices: 
-- Tool versions: 
-- Description: 
--
-- Dependencies: 
--
-- Revision: 
-- Revision 0.01 - File Created
-- Additional Comments: 
--
----------------------------------------------------------------------------------

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity fifo_dp is
GENERIC
(
ADDRESS_WIDTH : integer:=8;---8 bit
DATA_WIDTH : integer:=8 ---8 bit
);

port ( clk : in std_logic;
reset : in std_logic;
enr : in std_logic; --enable read,should be '0' when not in use.
enw : in std_logic; --enable write,should be '0' when not in use.
dataout : out std_logic_vector(DATA_WIDTH-1 downto 0); --output data
datain : in std_logic_vector (DATA_WIDTH-1 downto 0); --input data
empty : out std_logic; --set as '1' when the queue is empty
err : out std_logic;
full : out std_logic --set as '1' when the queue is full
);
end fifo;

architecture Behavioral of fifo_dp is

type memory_type is array (0 to ((2**ADDRESS_WIDTH)-1)) of std_logic_vector(DATA_WIDTH-1 downto 0);


-----distributed-------
signal memory : memory_type ;-- :=(others => (others => '0')); --memory for queue.----- 
signal readptr,writeptr : std_logic_vector(ADDRESS_WIDTH-1 downto 0); --read and write pointers.
signal full0 : std_logic;
signal empty0 : std_logic;

begin
full <= full0;
empty <= empty0; 

fifo0: process(clk,reset)
begin
if reset='1' then

readptr <= (others => '0');
writeptr <= (others => '0');
empty0 <='1';
full0<='0';
err<='0';


elsif rising_edge(clk) then 

if (writeptr + '1' = readptr) then 
full0<='1';
else
full0<='0';
end if ;

if (readptr = writeptr ) then 
empty0<='1';
else
empty0<='0';
end if ; 

if (empty0='0' and enr='1') or (full0='0' and enw='1') then 
err<='1';
end if ; 

if enw='1' and full0='0' then 
memory (conv_integer(writeptr)) <= datain ;
writeptr <= writeptr + '1' ;
end if ; 

if enr='1' and empty0='0' then 
dataout <= memory (conv_integer(readptr));
readptr <= readptr + '1' ;
end if ; 

end if; 

end process;
end Behavioral;