-----------------------------------------------------------------------------
-- Author: Xiaofei Vivien Dong
-- Course: ee552
-- Project: CDMA based communication systems
-----------------------------------------------------------------------------
-- the musr_despeader decodes the frame data from scrambling.  input bit rate
-- 25/4MHz, output 25/32Mhz bps.
-----------------------------------------------------------------------------
-- Total logic cells used:                         15/1152   (  1%)
-- 
-- in transmitter, the bit '1' is mapped to x"0f", '0' is mapped to x"f0";

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
library work;
use work.CDMA_pkg.all;

entity musr_despreader is
  
  generic (
    code_width : positive := 8);

  port (
    resetn     : in  std_logic;
    clock      : in  std_logic;         -- shiftin_en
    shiftin_en : in  std_logic;
    dataout_en : in  std_logic;
    bitin      : in  std_logic;
    error_detected: out std_logic;
    bitout     : out std_logic);

end musr_despreader;

architecture despreading of musr_despreader is

  signal framedata : std_logic_vector(7 downto 0);
  constant scramble_code : std_logic_vector(7 downto 0)     := x"0f";
  constant not_scramble_code : std_logic_vector(7 downto 0) := x"f0";
  signal data : std_logic; 

begin  -- despreader

  collect8bit : s2preg generic map (
    width => code_width)
    port map (
      resetn   => resetn,
      clock    => clock,
      enable   => shiftin_en,
      bitin    => bitin,
      frameout => framedata);

	with framedata select
		data <= '1' when scramble_code,
				'0' when others;

	with framedata select
		error_detected <= 	'0' when scramble_code,
							'0' when not_scramble_code,
							'1' when others;

--  comparing: process
--    begin
--      if framedata = scramble_code then
--        data <= '1';
--        error_detected <= '0';
--      elsif framedata = not_scramble_code then
--        data <= '0';
--        error_detected <= '0';
--        else
--          error_detected <= '1';
--      end if;
--    end process;

    latchout : dff_en port map (
      resetn => resetn,
      clock  => clock,
      enable => dataout_en,
      d      => data,
      q      => bitout);
    
end despreading;