Subversion Repositories viterbi_decoder_axi4s

--!

--! Copyright (C) 2011 - 2012 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  Trellis parameter calculations (e.g., transitions, init values).

--! @author Markus Fehrenz

--! @date   2011/07/27

--!

--!

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_param_derived.all;

use dec_viterbi.pkg_types.all;

package pkg_trellis is

        type t_prev_base       is array (1 downto 0) of std_logic_vector(BW_TRELLIS_STATES - 1 downto 0);

        type t_previous_states is array (NUMBER_TRELLIS_STATES - 1 downto 0) of t_prev_base;

        type t_trans_base  is array (1 downto 0) of std_logic_vector(NUMBER_PARITY_BITS - 1 downto 0);

        type t_transitions is array (NUMBER_TRELLIS_STATES - 1 downto 0) of t_trans_base;

        type t_trans_base_signed  is array (1 downto 0) of std_logic_vector(NUMBER_PARITY_BITS downto 0);

        type t_transitions_signed is array (NUMBER_TRELLIS_STATES - 1 downto 0) of t_trans_base_signed;

        --

        -- This function calculates the previous states of each state.

        -- The values are used to connect the ACS units.

        --

        function calc_previous_states return t_previous_states;

        --

        -- This function calculates corresponding transitions to a trellis sate.

        -- The values are used to connect branch units to ACS units.

        --

        function calc_transitions     return t_transitions;

        --

        -- This function calculates the initialization values for trellis metrics.

        -- The values are used as a constant and written to the ACS unit, every time a new block arrives.

        --

        function calc_initialize      return t_node_s;

        constant PREVIOUS_STATES    : t_previous_states := calc_previous_states;

        constant TRANSITIONS        : t_transitions     := calc_transitions;

        constant INITIALIZE_TRELLIS : t_node_s          := calc_initialize;

end package pkg_trellis;

package body pkg_trellis is

        function calc_previous_states return t_previous_states is

                variable v_prev_states       : t_previous_states := (others=>(others=>(others => '0')));

                variable v_state0, v_state1  : std_logic_vector(BW_TRELLIS_STATES - 1 downto 0);

        begin

                for i in NUMBER_TRELLIS_STATES - 1 downto 0 loop

                        v_state0 := std_logic_vector(to_unsigned(i,BW_TRELLIS_STATES));

                        v_state1 := v_state0(BW_TRELLIS_STATES - 2 downto 0) & '0';

                        v_prev_states(i)(0) := v_state1;

                        v_state1 := v_state0(BW_TRELLIS_STATES - 2 downto 0) & '1';

                        v_prev_states(i)(1) := v_state1;

                end loop;

        return v_prev_states;

        end function calc_previous_states;

        function calc_transitions return t_transitions is

                variable v_transitions     : t_transitions_signed := (others => (others => (others => '0')));

                variable v_transitions_out : t_transitions := (others => (others => (others => '0')));

                variable v_one_transition  : std_logic_vector(NUMBER_PARITY_BITS - 1 downto 0);

                variable v_next_state      : unsigned(ENCODER_MEMORY_DEPTH - 1 downto 0) := (others => '0');

                variable v_state, v_states : unsigned(ENCODER_MEMORY_DEPTH downto 0);

                variable v_bit             : std_logic := '0';

        begin

                --

                -- It is possible to reduce code size at this stage, if feedback is handled differently,

                -- but the complexity will increase.

                --

                for i in NUMBER_TRELLIS_STATES - 1 downto 0 loop

                        --

                        -- for input : 0

                        -- determine correct input with feedback

                        --

                        v_next_state := to_unsigned(i,ENCODER_MEMORY_DEPTH) and to_unsigned(FEEDBACK_POLYNOMIAL, ENCODER_MEMORY_DEPTH);

                        for k in ENCODER_MEMORY_DEPTH - 1 downto 0 loop

                                v_bit := v_bit xor v_next_state(k);

                        end loop;

                        v_state(ENCODER_MEMORY_DEPTH)              := v_bit;

                        v_state(ENCODER_MEMORY_DEPTH - 1 downto 0) := to_unsigned(i,ENCODER_MEMORY_DEPTH);

                        v_next_state := v_state(ENCODER_MEMORY_DEPTH downto 1);

                        v_bit := '0';

                        -- determine paritybits

                        for j in NUMBER_PARITY_BITS - 1 downto 0 loop

                                v_states := v_state and to_unsigned(PARITY_POLYNOMIALS(j), ENCODER_MEMORY_DEPTH + 1);

                                for k in ENCODER_MEMORY_DEPTH downto 0 loop

                                        v_bit := v_bit xor v_states(k);

                                end loop;

                                v_one_transition(j) := v_bit;

                                v_bit := '0';

                        end loop;

                        -- decide where to save the parity result

                        if v_transitions(to_integer(v_next_state))(1)(NUMBER_PARITY_BITS) = '0' then

                                 v_transitions(to_integer(v_next_state))(1)(NUMBER_PARITY_BITS) := '1';

                                 v_transitions(to_integer(v_next_state))(1)(NUMBER_PARITY_BITS - 1 downto 0) := v_one_transition;

                        else

                                 v_transitions(to_integer(v_next_state))(0)(NUMBER_PARITY_BITS - 1 downto 0) := v_one_transition;

                        end if;

                        --

                        -- for input: 1

                        -- determine correct input with feedback

                        --

                        v_next_state := to_unsigned(i,ENCODER_MEMORY_DEPTH) and to_unsigned(FEEDBACK_POLYNOMIAL, ENCODER_MEMORY_DEPTH);

                        for k in ENCODER_MEMORY_DEPTH - 1 downto 0 loop

                                v_bit := v_bit xor v_next_state(k);

                        end loop;

                        v_state(ENCODER_MEMORY_DEPTH)              := '1' xor v_bit;

                        v_state(ENCODER_MEMORY_DEPTH - 1 downto 0) := to_unsigned(i,ENCODER_MEMORY_DEPTH);

                        v_next_state := v_state(ENCODER_MEMORY_DEPTH downto 1);

                        v_bit := '0';

                        -- determine paritybits

                        for j in NUMBER_PARITY_BITS - 1 downto 0 loop

                                v_states := v_state and to_unsigned(PARITY_POLYNOMIALS(j), ENCODER_MEMORY_DEPTH + 1);

                                for k in ENCODER_MEMORY_DEPTH downto 0 loop

                                        v_bit := v_bit xor v_states(k);

                                end loop;

                                v_one_transition(j) := v_bit;

                                v_bit := '0';

                        end loop;

                        -- decide where to save parity result

                        if v_transitions(to_integer(v_next_state))(1)(NUMBER_PARITY_BITS) = '0' then

                                 v_transitions(to_integer(v_next_state))(1)(NUMBER_PARITY_BITS) := '1';

                                 v_transitions(to_integer(v_next_state))(1)(NUMBER_PARITY_BITS - 1 downto 0) := v_one_transition;

                        else

                                 v_transitions(to_integer(v_next_state))(0)(NUMBER_PARITY_BITS - 1 downto 0) := v_one_transition;

                        end if;

                end loop;

                -- truncate, the bit, used to decide where to save parity result

                for i in NUMBER_TRELLIS_STATES - 1 downto 0 loop

                        v_transitions_out(i)(1) := v_transitions(i)(1)(NUMBER_PARITY_BITS - 1 downto 0);

                        v_transitions_out(i)(0) := v_transitions(i)(0)(NUMBER_PARITY_BITS - 1 downto 0);

                end loop;

                return v_transitions_out;

        end function calc_transitions;

        function calc_initialize return t_node_s is

                variable v_initialize : t_node_s;

        begin

                v_initialize(0) := to_signed(0, BW_MAX_PROBABILITY);

                for i in NUMBER_TRELLIS_STATES - 1 downto 1 loop

                        v_initialize(i) := to_signed(- 2 ** (BW_MAX_PROBABILITY - 2), BW_MAX_PROBABILITY);

                end loop;

        return v_initialize;

        end function calc_initialize;

end package body pkg_trellis;