info regarding digital low pass fir filter design in VHDL...

hello...
As part of my final year project, iam working on digital low pass
FIR filter design in VHDL.
I have written the code for the filter design in VHDL.but, I have some
problem in debugging it.
I will be very thankful if you can debug it and send me back..
I worked on ALTERA MAX+PLUSII.
thanku...
Here,iam sending the code...

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use IEEE.std_logic_unsigned.all;
entity FIR_filter1 is port(
rst: in std_logic;
clk: in std_logic;
coef_ld: in std_logic;
start: in std_logic;
o_enable: in std_logic;
bypass: in std_logic;
Xn_in: in std_logic_vector(3 downto 0);

Yn_in: in std_logic_vector(15 downto 0);

Xn_out: out std_logic_vector(3 downto 0);

Yn_out: out std_logic_vector(15 downto 0)
);
end FIR_filter1;
architecture BEH of FIR_filter1 is
constant K: integer := 2;
-- circuit has four stages
-- use type and subtype to define the complex signals
subtype bit4 is std_logic_vector(3 downto 0);
subtype bit8 is std_logic_vector(7 downto 0);
subtype bit16 is std_logic_vector(15 downto 0);
type klx4 is array (K downto 0) of bit4;
type kx8 is array (K-1 downto 0) of bit8;
type klx8 is array (K downto 0) of bit8;
type kx16 is array (K-1 downto 0) of bit16;
type klx16 is array (K downto 0) of bit16;
-- define signal in type of arrays
signal REG1, REG2, COEF : klx4;
signal MULT8 : kx8;
signal MULT16 : kx16;
signal sumx : klx16;
signal Xn_tmp : bit4;
signal Yn_tmp : bit16;
begin
-- initialize the first stage of FIR circuit
REG2(K) <= Xn_in when (start='1')
else ("0000");
REG1(K) <= ("0000");
sumx(K) <= Yn_in;
COEF(K) <= Xn_in;
-- start the computation, use generate to obtain the
-- multiple stages
gen8: for j in K-1 downto 0 generate
stages: process (rst, clk)
begin
if (rst='0') then
REG1(j) <= ("0000");
REG2(j) <= ("0000");
COEF(j) <= ("0000");
MULT16(j) <= ("0000000000000000");
sumx(j) <= ("0000000000000000");
elsif (clk'event and clk ='1') then
REG1(j) <= REG2(j+1);
REG2(j) <= REG1(j);
if (coef_ld = '1') then
COEF(j) <= COEF(j+1);
end if;
MULT8(j) <= signed(REG1(j))*signed(COEF(j));
MULT16(j)(7 downto 0) <= MULT8(j);
if (MULT8(j)(7)='0') then
MULT16(j)(15 downto <= "00000000";
else MULT16(j)(15 downto <= "11111111";
end if;
sumx(j) <= signed(MULT16(j))+signed(sumx(j+1));
end if;
end process;
end generate;
-- control the outputs by concurrent statements
Xn_tmp <= Xn_in when bypass = '1' else
REG2(0) when coef_ld = '0'
else COEF(0);
Yn_tmp <= Yn_in when bypass = '1' else
sumx(0);
Xn_out <= Xn_tmp when o_enable = '0' else
(Xn_out'range => 'Z');
Yn_out <= Yn_tmp when o_enable = '0' else
(Yn_out'range => 'Z');
end BEH;

dhaanya nair