Library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use work.SIGNED_ARITH.all;
use work.coeffs.all;

entity fir is
 port(clk,reset: in std_logic;
      sample: in signed ( 7 downto 0);
      result: out signed ( 16 downto 0));
end fir;

architecture beh of fir is 
begin
     fir_main :process
      type shift_arr is array (16 downto 0) of signed (7 downto 0);
      variable tmp,old:signed( 7 downto 0);
      variable pro:signed (16 downto 0);
      variable acc:signed (16 downto 0);
      variable shift:shift_arr;
begin
     reset_loop:loop
     for i in 0 to 15 loop --zero out the shift register
        shift(i):=(others=>'0');
     end loop;
     result<=(others=>'0');
     wait until clk'event and clk='1';
     if reset='1' then exit reset_loop;
     end if;
     main:loop
     tmp:=sample;
     pro:=tmp*coefs(0);
     acc:=pro;
     for i in 15 downto 0 loop
     old:=shift(i);
     pro:=old*coefs(i+1);
     acc:=acc+pro;
     shift(i+1):=shift(i);
     end loop;
     shift(0):=tmp;
     result<=acc;
     wait until clk'event and clk='1';
     if reset='1' then exit reset_loop;
     end if;
     end loop main;
   end loop reset_loop;
  end process;
 end beh;