--************************************************************************

-- - H/W Development Group

-- ************************************************************************

--

-- Title: 256*8 Contant Access Memory (CAM)

--

-- Created: Mon Aug 28 12:14:47 2000

-- Author: DEEPAK GEORGE

-- Source File Name: cam256.vhd

--

-- $Id: cam256.vhd,v 1.1 2000/08/28 12:14:47 acts Exp $

--

-- Description: This is the code for a Content Access Type of memory,

-- it has got a 256*8 bit TAG table and a 256*8 Data table. CAM

-- will match the contents of the TAG with the datain and if a match is

-- found HIT is made high and the appropriate data is outputed on the

-- dataout port.

--

-- Revision History:

--

-- $Log: cam256.vhd,v $

--

-- ************************************************************************

library IEEE, STD;

use IEEE.std_logic_1164.all;

use IEEE.std_logic_components.all;

use IEEE.std_logic_arith.all;

use IEEE.std_logic_misc.all;

use IEEE.std_logic_unsigned.all;

entity cam256 is

port (clk : in std_logic; -- Clock

rst : in std_logic; -- Reset

rd_b : in std_logic; -- Read

wr_b : in std_logic; -- Write

datain : in std_logic_vector(7 downto 0);-- data in

-- during write.

tagin : in std_logic_vector(7 downto 0);-- Tag Data

data_out : out std_logic_vector(7 downto 0);-- Data out

full : out std_logic; -- Stack Full

hit : out std_logic -- Found Match

);

end cam256;

architecture cam256_A of cam256 is

type ram_array is aray (0 to 255 ) of std_logic_vector(7 downto 0);

signal tag : ram_array;

signal data : ram_array;

signal count : integer range 0 to 255;

begin

main : process(clk,rst)

begin

if (rst = '1') then

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

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

count<= 0;

full <= '0';

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

-- Stack Write Operation

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

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

if (wr_b = '0' and rd_b = '1') then

if ( count = 255 ) then

full <= '1';

else

tag (conv_integer (count))<= tin;

data(conv_integer (count))<= datain;

count <= count +1;

end if;

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

-- Stack CAM Read Operation

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

elsif (wr_b = '1' and rd_b = '0') then

for addr 0 to 255 loop -- Check for data

if ( tagin = tag(conv_integer (addr)) then

Hit <= '1'; -- Found Match

data_out <= data ( conv_integer (addr));

else

hit <= '0'; -- No match found

end if;

end loop;

end if

end if;

end process;

end cam256_A;