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

library XilinxCoreLib;
use XilinxCoreLib.all;

entity CRC32 is
    Port ( Clock: in std_logic;
	 		  Init : in std_logic;
			  Data : in std_logic_vector(7 downto 0);
			  CRC  : out std_logic_vector(31 downto 0)
			);
end CRC32;

architecture Behavioral of CRC32 is

-- signals
--------------------------------------------
	signal ETH_DAT: std_logic_vector(7 downto 0);
	signal ROM_ADR: std_logic_vector(7 downto 0);
	signal CRC_VAR: std_logic_vector(31 downto 0);
	signal CRC_DEL: std_logic_vector(31 downto 0);
	signal CRC_SFT: std_logic_vector(31 downto 0);

	signal ROM_DAT: std_logic_vector(31 downto 0);
	alias  CRC_ROM: std_logic_vector(7 downto 0) is CRC_VAR(7 downto 0);


component ROM
	port (
	a: in std_logic_vector(7 downto 0);
	spo: out std_logic_vector(31 downto 0)
		  );
end component;

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

begin

-- Latch input data
-------------------------------------------
	process(Clock, Data)
	begin
		if (Clock'event and Clock = '0') then
			ETH_DAT <= Data;
		end if;
	end process;
-------------------------------------------

-- Initialize CRC variable
-------------------------------------------
	process(Clock, Init, CRC_DEL)
	begin
		if (Clock'event and Clock='0') then
			if (Init = '1') then
				CRC_VAR <= x"FFFFFFFF";
			else
				CRC_VAR <= CRC_DEL;
			end if;
		end if;
	end process;
-------------------------------------------

-- Data mapping
-------------------------------------------
	ROM_ADR <= ETH_DAT xor CRC_ROM;

	CRC_SFT(31 downto 24) <= x"00";
	CRC_SFT(23 downto 0) <= CRC_VAR(31 downto 8);
-------------------------------------------

-- ROM data
-------------------------------------------
U0:	ROM
		port map (
			a => ROM_ADR,
			spo => ROM_DAT);
-------------------------------------------

-- Copy CRC variable
-------------------------------------------
	process(Clock, CRC_SFT, ROM_DAT)
	begin
		if (Clock'event and Clock = '1') then
			CRC_DEL <= CRC_SFT xor ROM_DAT;
		end if;
	end process;
-------------------------------------------

-- Final result
-------------------------------------------
	CRC <= CRC_DEL xor x"FFFFFFFF";
-------------------------------------------

end Behavioral;