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--------------------------------------------------------------------------------
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--
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-- Copyright 2020
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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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-- Licensed under the Apache License, Version 2.0 (the "License");
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-- you may not use this file except in compliance with the License.
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-- You may obtain a copy of the License at
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--
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-- http://www.apache.org/licenses/LICENSE-2.0
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--
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-- Unless required by applicable law or agreed to in writing, software
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-- distributed under the License is distributed on an "AS IS" BASIS,
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-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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-- See the License for the specific language governing permissions and
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-- limitations under the License.
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--
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--------------------------------------------------------------------------------
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-- Author:
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-- . Eric Kooistra
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-- Purpose:
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-- . Linear Feedback Shift Register based pseudo random sequence generation.
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-- Interface:
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-- . [n/a]
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-- Description:
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-- . Based on Xilinx application note xapp052.
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LIBRARY IEEE;
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USE IEEE.std_logic_1164.ALL;
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USE IEEE.numeric_std.ALL;
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USE work.common_pkg.ALL;
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PACKAGE common_lfsr_sequences_pkg IS
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CONSTANT c_common_lfsr_max_nof_feedbacks : NATURAL := 6;
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CONSTANT c_common_lfsr_first : NATURAL := 1; -- also support n = 1 and 2 in addition to n >= 3
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TYPE t_FEEDBACKS IS ARRAY (c_common_lfsr_max_nof_feedbacks-1 DOWNTO 0) OF NATURAL;
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TYPE t_SEQUENCES IS ARRAY (NATURAL RANGE <>) OF t_FEEDBACKS;
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-- XNOR feedbacks for n = 1:
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-- (0,0,0,0,0, 0) yields repeat <1>
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-- (0,0,0,0,0, 1) yields repeat <0, 1>
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-- XNOR feedbacks for n = 2:
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-- (0,0,0,0, 0, 1) yields repeat <1, 2>
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-- (0,0,0,0, 0, 2) yields repeat <0, 1, 3, 2>
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-- (0,0,0,0, 2, 1) yields repeat <0, 1, 2>
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-- XNOR feedbacks from outputs for n = 3 .. 72 from Xilinx xapp052.pdf (that lists feedbacks for in total 168 sequences)
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CONSTANT c_common_lfsr_sequences : t_SEQUENCES := ((0,0,0,0,0, 1), -- 1 : <0, 1>
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(0,0,0,0, 0, 2), -- 2 : <0, 1, 3, 2>
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(0,0,0,0, 3, 2), -- 3
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(0,0,0,0, 4, 3), -- 4
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(0,0,0,0, 5, 3), -- 5
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(0,0,0,0, 6, 5), -- 6
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(0,0,0,0, 7, 6), -- 7
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(0,0, 8, 6, 5, 4), -- 8
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(0,0,0,0, 9, 5), -- 9
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(0,0,0,0, 10, 7), -- 10
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(0,0,0,0, 11, 9), -- 11
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(0,0, 12, 6, 4, 1), -- 12
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(0,0, 13, 4, 3, 1), -- 13
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(0,0, 14, 5, 3, 1), -- 14
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(0,0,0,0, 15,14 ), -- 15
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(0,0, 16,15,13, 4), -- 16
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(0,0,0,0, 17,14 ), -- 17
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(0,0,0,0, 18,11 ), -- 18
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(0,0, 19, 6, 2, 1), -- 19
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(0,0,0,0, 20,17 ), -- 20
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(0,0,0,0, 21,19 ), -- 21
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(0,0,0,0, 22,21 ), -- 22
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(0,0,0,0, 23,18 ), -- 23
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(0,0, 24,23,22,17), -- 24
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(0,0,0,0, 25,22 ), -- 25
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(0,0, 26, 6, 2, 1), -- 26
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(0,0, 27, 5, 2, 1), -- 27
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(0,0,0,0, 28,25 ), -- 28
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(0,0,0,0, 29,27 ), -- 29
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(0,0, 30, 6, 4, 1), -- 30
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(0,0,0,0, 31,28 ), -- 31
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(0,0, 32,22, 2, 1), -- 32
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(0,0,0,0, 33,20 ), -- 33
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(0,0, 34,27, 2, 1), -- 34
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(0,0,0,0, 35,33 ), -- 35
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(0,0,0,0, 36,25 ), -- 36
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( 37, 5, 4, 3, 2, 1), -- 37
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(0,0, 38, 6, 5, 1), -- 38
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(0,0,0,0, 39,35 ), -- 39
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(0,0, 40,38,21,19), -- 40
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(0,0,0,0, 41,38 ), -- 41
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(0,0, 42,41,20,19), -- 42
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(0,0, 43,42,38,37), -- 43
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(0,0, 44,43,18,17), -- 44
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(0,0, 45,44,42,41), -- 45
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(0,0, 46,45,26,25), -- 46
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(0,0,0,0, 47,42 ), -- 47
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(0,0, 48,47,21,20), -- 48
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(0,0,0,0, 49,40 ), -- 49
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(0,0, 50,49,24,23), -- 50
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(0,0, 51,50,36,35), -- 51
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(0,0,0,0, 52,49 ), -- 52
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(0,0, 53,52,38,37), -- 53
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(0,0, 54,53,18,17), -- 54
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(0,0,0,0, 55,31 ), -- 55
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(0,0, 56,55,35,34), -- 56
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(0,0,0,0, 57,50 ), -- 57
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(0,0,0,0, 58,39 ), -- 58
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(0,0, 59,58,38,37), -- 59
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(0,0,0,0, 60,59 ), -- 60
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(0,0, 61,60,46,45), -- 61
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(0,0, 62,61, 6, 5), -- 62
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(0,0,0,0, 63,62 ), -- 63
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(0,0, 64,63,61,60), -- 64
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(0,0,0,0, 65,47 ), -- 65
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(0,0, 66,65,57,56), -- 66
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(0,0, 67,66,58,57), -- 67
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(0,0,0,0, 68,59 ), -- 68
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(0,0, 69,67,42,40), -- 69
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(0,0, 70,69,55,54), -- 70
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(0,0,0,0, 71,65 ), -- 71
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(0,0, 72,66,25,19)); -- 72
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-- Procedure for calculating the next PSRG and COUNTER sequence value
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PROCEDURE common_lfsr_nxt_seq(CONSTANT c_lfsr_nr : IN NATURAL;
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CONSTANT g_incr : IN INTEGER;
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in_en : IN STD_LOGIC;
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in_req : IN STD_LOGIC;
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in_dat : IN STD_LOGIC_VECTOR;
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prsg : IN STD_LOGIC_VECTOR;
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cntr : IN STD_LOGIC_VECTOR;
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SIGNAL nxt_prsg : OUT STD_LOGIC_VECTOR;
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SIGNAL nxt_cntr : OUT STD_LOGIC_VECTOR);
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-- Use lfsr part of common_lfsr_nxt_seq to make a random bit generator function
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-- . width of lfsr selects the LFSR sequence
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-- . initialized lfsr with (OTHERS=>'0')
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-- . use lfsr(lfsr'HIGH) as random bit
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FUNCTION func_common_random(lfsr : STD_LOGIC_VECTOR) RETURN STD_LOGIC_VECTOR;
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END common_lfsr_sequences_pkg;
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PACKAGE BODY common_lfsr_sequences_pkg IS
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PROCEDURE common_lfsr_nxt_seq(CONSTANT c_lfsr_nr : IN NATURAL;
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CONSTANT g_incr : IN INTEGER;
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in_en : IN STD_LOGIC;
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in_req : IN STD_LOGIC;
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in_dat : IN STD_LOGIC_VECTOR;
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prsg : IN STD_LOGIC_VECTOR;
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cntr : IN STD_LOGIC_VECTOR;
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SIGNAL nxt_prsg : OUT STD_LOGIC_VECTOR;
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SIGNAL nxt_cntr : OUT STD_LOGIC_VECTOR) IS
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VARIABLE v_feedback : STD_LOGIC;
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BEGIN
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nxt_prsg <= prsg;
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nxt_cntr <= cntr;
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IF in_en='0' THEN -- init reference value
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nxt_prsg <= in_dat;
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nxt_cntr <= in_dat;
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ELSIF in_req='1' THEN -- next reference value
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-- PRSG shift
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nxt_prsg <= prsg(prsg'HIGH-1 DOWNTO 0) & '0';
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-- PRSG feedback
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v_feedback := '0';
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FOR I IN c_common_lfsr_max_nof_feedbacks-1 DOWNTO 0 LOOP
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IF c_common_lfsr_sequences(c_lfsr_nr)(I) /= 0 THEN
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v_feedback := v_feedback XOR prsg(c_common_lfsr_sequences(c_lfsr_nr)(I)-1);
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END IF;
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END LOOP;
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nxt_prsg(0) <= NOT v_feedback;
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-- COUNTER
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nxt_cntr <= INCR_UVEC(cntr, g_incr);
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END IF;
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END common_lfsr_nxt_seq;
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FUNCTION func_common_random(lfsr : STD_LOGIC_VECTOR) RETURN STD_LOGIC_VECTOR IS
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CONSTANT c_lfsr_nr : NATURAL := lfsr'LENGTH - c_common_lfsr_first;
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VARIABLE v_nxt_lfsr : STD_LOGIC_VECTOR(lfsr'RANGE);
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VARIABLE v_feedback : STD_LOGIC;
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BEGIN
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-- shift
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v_nxt_lfsr := lfsr(lfsr'HIGH-1 DOWNTO 0) & '0';
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-- feedback
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v_feedback := '0';
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FOR I IN c_common_lfsr_max_nof_feedbacks-1 DOWNTO 0 LOOP
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IF c_common_lfsr_sequences(c_lfsr_nr)(I) /= 0 THEN
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v_feedback := v_feedback XOR lfsr(c_common_lfsr_sequences(c_lfsr_nr)(I)-1);
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END IF;
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END LOOP;
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v_nxt_lfsr(0) := NOT v_feedback;
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RETURN v_nxt_lfsr;
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END func_common_random;
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END common_lfsr_sequences_pkg;
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