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-------------------------------------------------------------------------------
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--
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-- Copyright (C) 2012
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-- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>
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-- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands
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--
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-- This program is free software: you can redistribute it and/or modify
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-- it under the terms of the GNU General Public License as published by
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-- the Free Software Foundation, either version 3 of the License, or
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-- (at your option) any later version.
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--
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-- This program is distributed in the hope that it will be useful,
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-- but WITHOUT ANY WARRANTY; without even the implied warranty of
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-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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-- GNU General Public License for more details.
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--
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-- You should have received a copy of the GNU General Public License
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-- along with this program. If not, see <http://www.gnu.org/licenses/>.
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--
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-------------------------------------------------------------------------------
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-- Purpose: A FIR filter implementation.
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--
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-- Description: This unit instantiates a multiplier for every tap.
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-- All output of the mutipliers are added using an
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-- adder-tree structure.
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--
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-- Remarks: .
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--
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library IEEE, common_pkg_lib, astron_multiplier_lib, astron_requantize_lib, astron_adder_lib;
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use IEEE.std_logic_1164.ALL;
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use IEEE.numeric_std.ALL;
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--USE technology_lib.technology_select_pkg.ALL;
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use common_pkg_lib.common_pkg.ALL;
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use work.fil_pkg.ALL;
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entity fil_ppf_filter is
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generic (
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g_technology : NATURAL := 0;
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g_fil_ppf : t_fil_ppf;
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g_fil_ppf_pipeline : t_fil_ppf_pipeline
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);
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port (
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clk : in std_logic;
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rst : in std_logic;
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taps : in std_logic_vector;
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coefs : in std_logic_vector;
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result : out std_logic_vector
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);
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end fil_ppf_filter;
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architecture rtl of fil_ppf_filter is
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constant c_in_dat_w : natural := g_fil_ppf.backoff_w + g_fil_ppf.in_dat_w; -- add optional input backoff to fit output overshoot
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constant c_prod_w : natural := c_in_dat_w + g_fil_ppf.coef_dat_w - c_sign_w; -- skip double sign bit
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constant c_gain_w : natural := 0; -- no need for adder bit growth so fixed 0, because filter coefficients should have DC gain <= 1.
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-- The adder tree bit growth depends on DC gain of FIR coefficients, not on ceil_log2(g_fil_ppf.nof_taps).
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constant c_sum_w : natural := c_prod_w + c_gain_w;
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constant c_ppf_lsb_w : natural := c_sum_w - g_fil_ppf.out_dat_w;
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signal prod_vec : std_logic_vector(g_fil_ppf.nof_taps*c_prod_w-1 downto 0);
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signal adder_out : std_logic_vector(c_sum_w-1 downto 0) := (others => '0');
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signal requant_out : std_logic_vector(g_fil_ppf.out_dat_w-1 downto 0);
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signal in_taps : std_logic_vector(g_fil_ppf.in_dat_w*g_fil_ppf.nof_taps-1 downto 0); -- taps input data as stored in RAM
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signal in_taps_backoff : std_logic_vector( c_in_dat_w*g_fil_ppf.nof_taps-1 downto 0); -- taps input data with backoff as use in FIR
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begin
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in_taps <= taps; -- Use this help signal to create a 'HIGH downto 0 vector again.
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---------------------------------------------------------------
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-- GENERATE THE MUTIPLIERS
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---------------------------------------------------------------
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-- For every tap a unique multiplier is instantiated that
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-- multiplies the data tap with the corresponding filter coefficient
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gen_multipliers : for I in 0 to g_fil_ppf.nof_taps-1 generate
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in_taps_backoff((I+1)*c_in_dat_w-1 downto I*c_in_dat_w) <= resize_svec(in_taps((I+1)*g_fil_ppf.in_dat_w-1 downto I*g_fil_ppf.in_dat_w), c_in_dat_w);
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u_multiplier : entity astron_multiplier_lib.common_mult
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generic map (
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g_technology => g_technology,
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g_variant => "IP",
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g_in_a_w => c_in_dat_w,
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g_in_b_w => g_fil_ppf.coef_dat_w,
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g_out_p_w => c_prod_w,
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g_nof_mult => 1,
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g_pipeline_input => g_fil_ppf_pipeline.mult_input,
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g_pipeline_product => g_fil_ppf_pipeline.mult_product,
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g_pipeline_output => g_fil_ppf_pipeline.mult_output,
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g_representation => "SIGNED"
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)
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port map (
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rst => rst,
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clk => clk,
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clken => '1',
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in_a => in_taps_backoff((I+1)*c_in_dat_w-1 downto I*c_in_dat_w),
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in_b => coefs((I+1)*g_fil_ppf.coef_dat_w-1 downto I*g_fil_ppf.coef_dat_w),
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out_p => prod_vec((I+1)*c_prod_w-1 downto I*c_prod_w)
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);
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end generate;
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---------------------------------------------------------------
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-- ADDER TREE
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---------------------------------------------------------------
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-- The adder tree summarizes the outputs of all multipliers.
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u_adder_tree : entity astron_adder_lib.common_adder_tree(str)
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generic map (
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g_representation => "SIGNED",
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g_pipeline => g_fil_ppf_pipeline.adder_stage,
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g_nof_inputs => g_fil_ppf.nof_taps,
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g_dat_w => c_prod_w,
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g_sum_w => c_sum_w
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)
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port map (
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clk => clk,
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in_dat => prod_vec,
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sum => adder_out
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);
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u_requantize_addeer_output : entity astron_requantize_lib.common_requantize
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generic map (
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g_representation => "SIGNED",
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g_lsb_w => c_ppf_lsb_w,
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g_lsb_round => TRUE,
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g_lsb_round_clip => FALSE,
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g_msb_clip => FALSE,
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g_msb_clip_symmetric => FALSE,
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g_pipeline_remove_lsb => g_fil_ppf_pipeline.requant_remove_lsb,
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g_pipeline_remove_msb => g_fil_ppf_pipeline.requant_remove_msb,
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g_in_dat_w => c_sum_w,
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g_out_dat_w => g_fil_ppf.out_dat_w
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)
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port map (
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clk => clk,
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clken => '1',
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in_dat => adder_out,
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out_dat => requant_out,
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out_ovr => open
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);
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result <= RESIZE_SVEC(requant_out, result'LENGTH);
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end rtl;
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