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--!
--! Copyright (C) 2011 - 2014 Creonic GmbH
--!
--! This file is part of the Creonic Viterbi Decoder, which is distributed
--! under the terms of the GNU General Public License version 2.
--!
--! @file
--! @brief Derived parameters
--! @author Markus Fehrenz
--! @date 2011/07/04
--!
--! @details This constants are derived from constants defined in pkg_param.
--! In order to prevent errors, there is no user choice for these parameters.
--!
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
library dec_viterbi;
use dec_viterbi.pkg_param.all;
use dec_viterbi.pkg_helper.all;
package pkg_param_derived is
-- Calculation of constraint length.
function calc_constraint_length return natural;
-- Memory depth of the encoder shift register.
constant ENCODER_MEMORY_DEPTH : natural;
-- Number of trellis states corresponds to the nubmer of ACS units.
constant NUMBER_TRELLIS_STATES : natural;
-- Number of branch units for a single polynomial set
constant NUMBER_BRANCH_UNITS : natural;
-- Bitwidth constants are needed for type conversions
constant BW_TRELLIS_STATES : natural;
constant BW_MAX_WINDOW_LENGTH : natural;
constant BW_BRANCH_RESULT : natural;
constant BW_MAX_PROBABILITY : natural;
end package pkg_param_derived;
package body pkg_param_derived is
function calc_constraint_length return natural is
variable v_maximum : natural := 0;
begin
-- Find the position of the leftmost bit in the polynomials.
for i in NUMBER_PARITY_BITS - 1 downto 0 loop
v_maximum := max(v_maximum, no_bits_natural(PARITY_POLYNOMIALS(i)));
end loop;
v_maximum := max(v_maximum, no_bits_natural(FEEDBACK_POLYNOMIAL));
return v_maximum;
end function calc_constraint_length;
constant ENCODER_MEMORY_DEPTH : natural := calc_constraint_length - 1;
constant NUMBER_TRELLIS_STATES : natural := 2 ** ENCODER_MEMORY_DEPTH;
constant NUMBER_BRANCH_UNITS : natural := 2 ** NUMBER_PARITY_BITS;
constant BW_TRELLIS_STATES : natural := no_bits_natural(NUMBER_TRELLIS_STATES - 1);
constant BW_MAX_WINDOW_LENGTH : natural := no_bits_natural(MAX_WINDOW_LENGTH - 1);
constant BW_BRANCH_RESULT : natural := no_bits_natural((2 ** (BW_LLR_INPUT - 1)) * NUMBER_PARITY_BITS) + 1;
constant BW_MAX_PROBABILITY : natural := no_bits_natural(((2 ** (BW_LLR_INPUT - 1)) * NUMBER_PARITY_BITS) * 4 * ENCODER_MEMORY_DEPTH);
end package body pkg_param_derived;
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