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Scrambler and Descrambler VHDL source code

This page of VHDL source code covers Scrambler and descrambler vhdl code. The scrambler implemention is as per MATLAB scrambler source code mentioned in MATLAB source code section.

VHDL Code

-- Library Declaration
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
-- Entity Declaration
entity Scrambler is
port(clk : in std_logic; -- Processing Clock
reset : in std_logic; -- Asynchronous reset signal
load : in std_logic; -- Load signal to load the seed value into register
seed_in : in std_logic_vector(14 downto 0); -- Seed value to load into register
data_in : in std_logic; -- Input data to transmit
valid_in : in std_logic; -- Input data valid signal
data_out : out std_logic; -- Output data from the scrambler
valid_out : out std_logic -- Output valid signal
);
end Scrambler;
architecture behaviour of Scrambler is

Signal shift_reg_s : std_logic_vector(14 downto 0);
signal valid_in1 : std_logic;
signal data_in1 : std_logic;
begin

Process( clk,reset)
begin
if reset = '1' then
shift_reg_s <= (others => '0');
valid_in1 <= '0';
data_in1 <= '0';
valid_out <= '0';
data_out <= '0';
elsif clk'event and clk = '1' then
valid_in1 <= valid_in;
data_in1 <= data_in;
if load='1' then
Shift_reg_s(0) <= seed_in(14);
Shift_reg_s(1) <= seed_in(13);
Shift_reg_s(2) <= seed_in(12);
Shift_reg_s(3) <= seed_in(11);
Shift_reg_s(4) <= seed_in(10); --it loads initiation value into 15-bit register.
Shift_reg_s(5) <= seed_in(9);
Shift_reg_s(6) <= seed_in(8);
Shift_reg_s(7) <= seed_in(7);
Shift_reg_s(8) <= seed_in(6);
Shift_reg_s(9) <= seed_in(5);
Shift_reg_s(10) <= seed_in(4);
Shift_reg_s(11) <= seed_in(3);
Shift_reg_s(12) <= seed_in(2);
Shift_reg_s(13) <= seed_in(1);
Shift_reg_s(14) <= seed_in(0);
elsif valid_in = '1' then
Shift_reg_s(14) <= Shift_reg_s(13);
Shift_reg_s(13) <= Shift_reg_s(12); -- If valid input signal is high the register
Shift_reg_s(12) <= Shift_reg_s(11); -- contents are shifted by one bit and msb bit
Shift_reg_s(11) <= Shift_reg_s(10); -- is EX-OR with 14th bit and load it into 1st bit
Shift_reg_s(10) <= Shift_reg_s(9); -- position
Shift_reg_s(9) <= Shift_reg_s(8);
Shift_reg_s(8) <= Shift_reg_s(7);
Shift_reg_s(7) <= Shift_reg_s(6);
Shift_reg_s(6) <= Shift_reg_s(5);
Shift_reg_s(5) <= Shift_reg_s(4);
Shift_reg_s(4) <= Shift_reg_s(3);
Shift_reg_s(3) <= Shift_reg_s(2);
Shift_reg_s(2) <= Shift_reg_s(1);
Shift_reg_s(1) <= Shift_reg_s(0);
Shift_reg_s(0) <= Shift_reg_s(13) xor Shift_reg_s(14);
end if;
if valid_in1 = '1' then
data_out <= shift_reg_s(0) xor data_in1;
valid_out <= '1'; -- output port.
else
data_out <= '0';
valid_out <= '0';
end if;
end if;
end process;

end behaviour;

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