Subversion Repositories epc_rfid_transponder

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--     Politecnico di Torino                                              

--     Dipartimento di Automatica e Informatica             

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--

--     Title          : EPC Class1 Gen2 RFID Tag - 16-bit Pseudo-random Number Generator    

--

--     File name      : pseudoRNG.vhd 

--

--     Description    : Peudo-random number generator based on 31-bit LFSR.

--                      LFSR primitive polynomial: 1 + X^28 + X^31

--                      Better performance may be reached using a leap-forward

--                      LFSR implementation...!!!

--     

--     Authors        : Erwing R. Sanchez <erwing.sanchezsanchez@polito.it>

--

--     Rev. History   : 17 july 06 - First Draft 

--                                 

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library IEEE;

use IEEE.STD_LOGIC_1164.all;

use IEEE.std_logic_unsigned.all;

use IEEE.STD_LOGIC_ARITH.all;

entity prng is

  port (

    clk   : in  std_logic;

    rst_n : in  std_logic;

    init  : in  std_logic;

    cin   : in  std_logic_vector(30 downto 0);

    ce    : in  std_logic;

    cout  : out std_logic_vector(30 downto 0));

end prng;

architecture prng_arch of prng is

  signal lfsr31 : std_logic_vector(30 downto 0);

begin  -- prng16_arch

  LFSR : process (clk, rst_n)

  begin  -- process LFSR

    if rst_n = '0' then                 -- asynchronous reset (active low)

      lfsr31 <= (others => '0');

    elsif clk'event and clk = '1' then  -- rising clock edge

      if init = '1' then

        lfsr31 <= cin;

      elsif ce = '1' then               -- shift register;

        lfsr31(30 downto 1) <= lfsr31(29 downto 0);

        lfsr31(0)           <= lfsr31(30) xor lfsr31(27);

      end if;

    end if;

  end process LFSR;

  cout <= lfsr31;

end prng_arch;