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-- $Id: fir.vhdl,v 1.5 2008-06-26 06:16:04 arif_endro Exp $

-------------------------------------------------------------------------------

-- Title       : FIR Low pass filter

-- Project     : FM Receiver 

-------------------------------------------------------------------------------

-- File        : fir.vhdl

-- Author      : "Arif E. Nugroho" <arif_endro@yahoo.com>

-- Created     : 2004/10/30

-- Last update : 2005/03/11

-- Simulators  : 

-- Synthesizers: 

-- Target      : 

-------------------------------------------------------------------------------

-- Description : FIR low pass filter

-------------------------------------------------------------------------------

-- Copyright (C) 2004 Arif Endro Nugroho

-------------------------------------------------------------------------------

-- 

--      THIS SOURCE FILE MAY BE USED AND DISTRIBUTED WITHOUT RESTRICTION

-- PROVIDED THAT THIS COPYRIGHT STATEMENT IS NOT REMOVED FROM THE FILE AND THAT

-- ANY DERIVATIVE WORK CONTAINS THE ORIGINAL COPYRIGHT NOTICE AND THE

-- ASSOCIATED DISCLAIMER.

-- 

-------------------------------------------------------------------------------

-- 

--      THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

-- IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF

-- MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO

-- EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

-- SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

-- PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;

-- OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,

-- WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR

-- OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF

-- ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

-- 

-------------------------------------------------------------------------------

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

entity fir is

  port(

  clock  : in  bit;

  clear  : in  bit;

  fir_in : in  bit_vector (11 downto 0); -- <12,4,t>

  dmout  : out bit_vector (11 downto 0)  -- <12,4,t>

  );

end fir;

architecture structural of fir is

  component adder_15bit

  port (

  addend_15bit   : in  bit_vector (14 downto 0);

  augend_15bit   : in  bit_vector (14 downto 0);

  adder15_output : out bit_vector (15 downto 0)

  );

  end component;

  component adder_14bit

  port (

  addend_14bit   : in  bit_vector (13 downto 0);

  augend_14bit   : in  bit_vector (13 downto 0);

  adder14_output : out bit_vector (14 downto 0)

  );

  end component;

  component adder_13bit

  port (

  addend_13bit   : in  bit_vector (12 downto 0);

  augend_13bit   : in  bit_vector (12 downto 0);

  adder13_output : out bit_vector (13 downto 0)

  );

  end component;

  component adder_12bit

  port (

  addend_12bit   : in  bit_vector (11 downto 0);

  augend_12bit   : in  bit_vector (11 downto 0);

  adder12_output : out bit_vector (12 downto 0)

  );

  end component;

  signal  fir_out        : bit_vector (11 downto 0);

  signal  fir_in_01      : bit_vector (11 downto 0);

  signal  fir_in_02      : bit_vector (11 downto 0);

  signal  fir_in_03      : bit_vector (11 downto 0);

  signal  fir_in_04      : bit_vector (11 downto 0);

  signal  fir_in_05      : bit_vector (11 downto 0);

  signal  fir_in_06      : bit_vector (11 downto 0);

  signal  fir_in_07      : bit_vector (11 downto 0);

  signal  fir_in_08      : bit_vector (11 downto 0);

  signal  fir_in_09      : bit_vector (11 downto 0);

  signal  fir_in_10      : bit_vector (11 downto 0);

  signal  fir_in_11      : bit_vector (11 downto 0);

  signal  fir_in_12      : bit_vector (11 downto 0);

  signal  fir_in_13      : bit_vector (11 downto 0);

  signal  fir_in_14      : bit_vector (11 downto 0);

  signal  fir_in_15      : bit_vector (11 downto 0);

  signal  fir_in_16      : bit_vector (11 downto 0);

  signal  result_adder01 : bit_vector (12 downto 0);

  signal  result_adder02 : bit_vector (12 downto 0);

  signal  result_adder03 : bit_vector (12 downto 0);

  signal  result_adder04 : bit_vector (12 downto 0);

  signal  result_adder05 : bit_vector (12 downto 0);

  signal  result_adder06 : bit_vector (12 downto 0);

  signal  result_adder07 : bit_vector (12 downto 0);

  signal  result_adder08 : bit_vector (12 downto 0);

  signal  result_adder09 : bit_vector (13 downto 0);

  signal  result_adder10 : bit_vector (13 downto 0);

  signal  result_adder11 : bit_vector (13 downto 0);

  signal  result_adder12 : bit_vector (13 downto 0);

  signal  result_adder13 : bit_vector (14 downto 0);

  signal  result_adder14 : bit_vector (14 downto 0);

  signal  result_adder15 : bit_vector (15 downto 0);

begin

  fir_in_01  <= fir_in;

adder01 : adder_12bit

  port map (

  addend_12bit(11 downto 0)   => fir_in_01,

  augend_12bit(11 downto 0)   => fir_in_02,

  adder12_output              => result_adder01

  );

adder02 : adder_12bit

  port map (

  addend_12bit(11 downto 0)   => fir_in_03,

  augend_12bit(11 downto 0)   => fir_in_04,

  adder12_output              => result_adder02

  );

adder03 : adder_12bit

  port map (

  addend_12bit(11 downto 0)   => fir_in_05,

  augend_12bit(11 downto 0)   => fir_in_06,

  adder12_output              => result_adder03

  );

adder04 : adder_12bit

  port map (

  addend_12bit(11 downto 0)   => fir_in_07,

  augend_12bit(11 downto 0)   => fir_in_08,

  adder12_output              => result_adder04

  );

adder05 : adder_12bit

  port map (

  addend_12bit(11 downto 0)   => fir_in_09,

  augend_12bit(11 downto 0)   => fir_in_10,

  adder12_output              => result_adder05

  );

adder06 : adder_12bit

  port map (

  addend_12bit(11 downto 0)   => fir_in_11,

  augend_12bit(11 downto 0)   => fir_in_12,

  adder12_output              => result_adder06

  );

adder07 : adder_12bit

  port map (

  addend_12bit(11 downto 0)   => fir_in_13,

  augend_12bit(11 downto 0)   => fir_in_14,

  adder12_output              => result_adder07

  );

adder08 : adder_12bit

  port map (

  addend_12bit(11 downto 0)   => fir_in_15,

  augend_12bit(11 downto 0)   => fir_in_16,

  adder12_output              => result_adder08

  );

adder09 : adder_13bit

  port map (

  addend_13bit(12 downto 0)   => result_adder01,

  augend_13bit(12 downto 0)   => result_adder02,

  adder13_output              => result_adder09

  );

adder10 : adder_13bit

  port map (

  addend_13bit(12 downto 0)   => result_adder03,

  augend_13bit(12 downto 0)   => result_adder04,

  adder13_output              => result_adder10

  );

adder11 : adder_13bit

  port map (

  addend_13bit(12 downto 0)   => result_adder05,

  augend_13bit(12 downto 0)   => result_adder06,

  adder13_output              => result_adder11

  );

adder12 : adder_13bit

  port map (

  addend_13bit(12 downto 0)   => result_adder07,

  augend_13bit(12 downto 0)   => result_adder08,

  adder13_output              => result_adder12

  );

adder13 : adder_14bit

  port map (

  addend_14bit(13 downto 0)   => result_adder09,

  augend_14bit(13 downto 0)   => result_adder10,

  adder14_output              => result_adder13

  );

adder14 : adder_14bit

  port map (

  addend_14bit(13 downto 0)   => result_adder11,

  augend_14bit(13 downto 0)   => result_adder12,

  adder14_output              => result_adder14

  );

adder15 : adder_15bit

  port map (

  addend_15bit(14 downto 0)   => result_adder13,

  augend_15bit(14 downto 0)   => result_adder14,

  adder15_output              => result_adder15

  );

-- FIR constants that have effect on output trasition.

-- This constant if set to low values (e.g x < 1/8 ) will make 

-- the transition output more looks like steps, noise will be reduced

-- but it's loss of fidelity of output signal.

-- for example:

-- set values to 1/16 will make the output trasition more look's like step

-- than an curve.

-- Just try another values to see the result. ^_^

fir_out(11)    <= (result_adder15(15)); -- 1

fir_out(10)    <= (result_adder15(14)); -- 1/2

fir_out(09)    <= (result_adder15(13)); -- 1/4

fir_out(08)    <= (result_adder15(12)); -- 1/8

fir_out(07)    <= (result_adder15(11)); -- 1/16

fir_out(06)    <= (result_adder15(10));

fir_out(05)    <= (result_adder15(09));

fir_out(04)    <= (result_adder15(08));

fir_out(03)    <= (result_adder15(07));

fir_out(02)    <= (result_adder15(06));

fir_out(01)    <= (result_adder15(05));

fir_out(00)    <= (result_adder15(04));

-- 20080625

-- fixme

-- how to enable clear signal in here... :(

--   process (clock, clear)

   process (clock)

   begin

--   if    (clear = '1') then

   if ((clock = '1') and clock'event) then

--      dmout     <= (others => '0');

--   elsif (((clock = '1') and (not(clear) = '1')) and clock'event) then

        fir_in_02 <= fir_in_01;

        fir_in_03 <= fir_in_02;

        fir_in_04 <= fir_in_03;

        fir_in_05 <= fir_in_04;

        fir_in_06 <= fir_in_05;

        fir_in_07 <= fir_in_06;

        fir_in_08 <= fir_in_07;

        fir_in_09 <= fir_in_08;

        fir_in_10 <= fir_in_09;

        fir_in_11 <= fir_in_10;

        fir_in_12 <= fir_in_11;

        fir_in_13 <= fir_in_12;

        fir_in_14 <= fir_in_13;

        fir_in_15 <= fir_in_14;

        fir_in_16 <= fir_in_15;

        dmout     <= fir_out;

   end if;

   end process;

end structural;