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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 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;
constant TRANSITIONS : t_transitions;
constant INITIALIZE_TRELLIS : t_node_s;
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;
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 body pkg_trellis;
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