Subversion Repositories viterbi_decoder_axi4s

--!

--! 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;