pn_correlation.vhd

it describe how to develop the field programmable gate array

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

entity pn_correlation is
    generic (
        K : std_logic_vector (7 downto 0) := "10001101");
    port (
        clk, reset, pn_acq, data_ch : in  std_logic;
        pn_fnd                      : out std_logic;
        wr_data                     : out std_logic_vector (7 downto 0));

end pn_correlation;

architecture rtl of pn_correlation is
    signal sr_data : std_logic_vector(7 downto 0);
    
begin  -- rtl

    wr_data <= sr_data;

    
    -- Serial to parrallel converter
    process (clk, reset)
    begin  -- process
        if reset = '1' then             -- asynchronous reset (active high)
            sr_data <= (others => '0');
        elsif rising_edge(clk) then     -- rising clock edge
            sr_data <= data_ch & sr_data(7 downto 1);
        end if;
    end process;
    
    -- pn_rake
    pn_rake: process (clk, reset)
        variable result : std_logic_vector (7 downto 0);
        variable agree, disagree, correlation : integer;
    begin  -- process pn_rake
        if reset = '1' then             -- asynchronous reset (active high)
            pn_fnd <= '0';
        elsif rising_edge(clk) then     -- rising clock edge
            -- default
            pn_fnd <= '0';
            if pn_acq = '1' then
                for j in 0 to 7 loop
                    if K(j) = '1' then
                        result(j) := K(j) and sr_data(j);
                    else
                        result(j) := not K(j) and not sr_data(j);
                    end if;
                end loop;  -- j
                           -- 
                agree := 0;
                disagree := 0;

                for i in 0 to 7 loop
                    case result(i) is
                        when '0' =>
                            disagree := disagree + 1;
                        when '1' =>
                            agree := agree + 1;
                        when others => null;
                    end case;
                end loop;  -- i
                correlation := agree - disagree;

                if correlation = 8 then
                    pn_fnd <= '1';
                else
                    pn_fnd <= '0';
                end if;
            end if;
        end if;
    end process pn_rake;

end rtl;