Subversion Repositories common_pkg

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--
-- Copyright (C) 2019
-- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>
-- JIVE (Joint Institute for VLBI in Europe) <http://www.jive.nl/>
-- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU General Public License as published by
-- the Free Software Foundation, either version 3 of the License, or
-- (at your option) any later version.
--
-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-- GNU General Public License for more details.
--
-- You should have received a copy of the GNU General Public License
-- along with this program.  If not, see <http://www.gnu.org/licenses/>.
--
--------------------------------------------------------------------------------
 
-- Author:
-- . Eric Kooistra
-- Purpose:
-- . Linear Feedback Shift Register based pseudo random sequence generation.
-- Interface:
-- . [n/a]
-- Description:
-- . Based on Xilinx application note xapp052.
 
LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;
USE IEEE.numeric_std.ALL;
USE work.common_pkg.ALL;
 
PACKAGE common_lfsr_sequences_pkg IS
 
  CONSTANT c_common_lfsr_max_nof_feedbacks : NATURAL := 6;
  CONSTANT c_common_lfsr_first             : NATURAL := 1;  -- also support n = 1 and 2 in addition to n >= 3
 
  TYPE t_FEEDBACKS IS ARRAY (c_common_lfsr_max_nof_feedbacks-1 DOWNTO 0) OF NATURAL;
  TYPE t_SEQUENCES IS ARRAY (NATURAL RANGE <>) OF t_FEEDBACKS;
 
  -- XNOR feedbacks for n = 1:
  --   (0,0,0,0,0, 0) yields repeat <1>
  --   (0,0,0,0,0, 1) yields repeat <0, 1>
 
  -- XNOR feedbacks for n = 2:
  --   (0,0,0,0, 0, 1) yields repeat <1, 2>
  --   (0,0,0,0, 0, 2) yields repeat <0, 1, 3, 2>
  --   (0,0,0,0, 2, 1) yields repeat <0, 1, 2>
 
  -- XNOR feedbacks from outputs for n = 3 .. 72 from Xilinx xapp052.pdf (that lists feedbacks for in total 168 sequences)
  CONSTANT c_common_lfsr_sequences : t_SEQUENCES := ((0,0,0,0,0,               1),   -- 1 : <0, 1>
                                                     (0,0,0,0,              0, 2),   -- 2 : <0, 1, 3, 2>
                                                     (0,0,0,0,              3, 2),   -- 3
                                                     (0,0,0,0,              4, 3),   -- 4
                                                     (0,0,0,0,              5, 3),   -- 5
                                                     (0,0,0,0,              6, 5),   -- 6
                                                     (0,0,0,0,              7, 6),   -- 7
                                                     (0,0,            8, 6, 5, 4),   -- 8
                                                     (0,0,0,0,              9, 5),   -- 9
                                                     (0,0,0,0,             10, 7),   -- 10
                                                     (0,0,0,0,             11, 9),   -- 11
                                                     (0,0,           12, 6, 4, 1),   -- 12
                                                     (0,0,           13, 4, 3, 1),   -- 13
                                                     (0,0,           14, 5, 3, 1),   -- 14
                                                     (0,0,0,0,       15,14      ),   -- 15
                                                     (0,0,           16,15,13, 4),   -- 16
                                                     (0,0,0,0,       17,14      ),   -- 17
                                                     (0,0,0,0,       18,11      ),   -- 18
                                                     (0,0,           19, 6, 2, 1),   -- 19
                                                     (0,0,0,0,       20,17      ),   -- 20
                                                     (0,0,0,0,       21,19      ),   -- 21
                                                     (0,0,0,0,       22,21      ),   -- 22
                                                     (0,0,0,0,       23,18      ),   -- 23
                                                     (0,0,           24,23,22,17),   -- 24
                                                     (0,0,0,0,       25,22      ),   -- 25
                                                     (0,0,           26, 6, 2, 1),   -- 26
                                                     (0,0,           27, 5, 2, 1),   -- 27
                                                     (0,0,0,0,       28,25      ),   -- 28
                                                     (0,0,0,0,       29,27      ),   -- 29
                                                     (0,0,           30, 6, 4, 1),   -- 30
                                                     (0,0,0,0,       31,28      ),   -- 31
                                                     (0,0,           32,22, 2, 1),   -- 32
                                                     (0,0,0,0,       33,20      ),   -- 33
                                                     (0,0,           34,27, 2, 1),   -- 34
                                                     (0,0,0,0,       35,33      ),   -- 35
                                                     (0,0,0,0,       36,25      ),   -- 36
                                                     (         37, 5, 4, 3, 2, 1),   -- 37
                                                     (0,0,           38, 6, 5, 1),   -- 38
                                                     (0,0,0,0,       39,35      ),   -- 39
                                                     (0,0,           40,38,21,19),   -- 40
                                                     (0,0,0,0,       41,38      ),   -- 41
                                                     (0,0,           42,41,20,19),   -- 42
                                                     (0,0,           43,42,38,37),   -- 43
                                                     (0,0,           44,43,18,17),   -- 44
                                                     (0,0,           45,44,42,41),   -- 45
                                                     (0,0,           46,45,26,25),   -- 46
                                                     (0,0,0,0,       47,42      ),   -- 47
                                                     (0,0,           48,47,21,20),   -- 48
                                                     (0,0,0,0,       49,40      ),   -- 49
                                                     (0,0,           50,49,24,23),   -- 50
                                                     (0,0,           51,50,36,35),   -- 51
                                                     (0,0,0,0,       52,49      ),   -- 52
                                                     (0,0,           53,52,38,37),   -- 53
                                                     (0,0,           54,53,18,17),   -- 54
                                                     (0,0,0,0,       55,31      ),   -- 55
                                                     (0,0,           56,55,35,34),   -- 56
                                                     (0,0,0,0,       57,50      ),   -- 57
                                                     (0,0,0,0,       58,39      ),   -- 58
                                                     (0,0,           59,58,38,37),   -- 59
                                                     (0,0,0,0,       60,59      ),   -- 60
                                                     (0,0,           61,60,46,45),   -- 61
                                                     (0,0,           62,61, 6, 5),   -- 62
                                                     (0,0,0,0,       63,62      ),   -- 63
                                                     (0,0,           64,63,61,60),   -- 64
                                                     (0,0,0,0,       65,47      ),   -- 65
                                                     (0,0,           66,65,57,56),   -- 66
                                                     (0,0,           67,66,58,57),   -- 67
                                                     (0,0,0,0,       68,59      ),   -- 68
                                                     (0,0,           69,67,42,40),   -- 69
                                                     (0,0,           70,69,55,54),   -- 70
                                                     (0,0,0,0,       71,65      ),   -- 71
                                                     (0,0,           72,66,25,19));  -- 72
 
 
  -- Procedure for calculating the next PSRG and COUNTER sequence value
  PROCEDURE common_lfsr_nxt_seq(CONSTANT c_lfsr_nr : IN  NATURAL;
                                CONSTANT g_incr    : IN  INTEGER;
                                         in_en     : IN  STD_LOGIC;
                                         in_req    : IN  STD_LOGIC;
                                         in_dat    : IN  STD_LOGIC_VECTOR;
                                         prsg      : IN  STD_LOGIC_VECTOR;
                                         cntr      : IN  STD_LOGIC_VECTOR;
                                SIGNAL   nxt_prsg  : OUT STD_LOGIC_VECTOR;
                                SIGNAL   nxt_cntr  : OUT STD_LOGIC_VECTOR);
 
  -- Use lfsr part of common_lfsr_nxt_seq to make a random bit generator function
  -- . width of lfsr selects the LFSR sequence
  -- . initialized lfsr with (OTHERS=>'0')
  -- . use lfsr(lfsr'HIGH) as random bit
  FUNCTION func_common_random(lfsr : STD_LOGIC_VECTOR) RETURN STD_LOGIC_VECTOR;
 
END common_lfsr_sequences_pkg;
 
 
PACKAGE BODY common_lfsr_sequences_pkg IS
 
  PROCEDURE common_lfsr_nxt_seq(CONSTANT c_lfsr_nr : IN  NATURAL;
                                CONSTANT g_incr    : IN  INTEGER;
                                         in_en     : IN  STD_LOGIC;
                                         in_req    : IN  STD_LOGIC;
                                         in_dat    : IN  STD_LOGIC_VECTOR;
                                         prsg      : IN  STD_LOGIC_VECTOR;
                                         cntr      : IN  STD_LOGIC_VECTOR;
                                SIGNAL   nxt_prsg  : OUT STD_LOGIC_VECTOR;
                                SIGNAL   nxt_cntr  : OUT STD_LOGIC_VECTOR) IS
    VARIABLE v_feedback : STD_LOGIC;
  BEGIN
    nxt_prsg <= prsg;
    nxt_cntr <= cntr;
    IF in_en='0' THEN     -- init reference value
      nxt_prsg <= in_dat;
      nxt_cntr <= in_dat;
    ELSIF in_req='1' THEN   -- next reference value
      -- PRSG shift
      nxt_prsg    <= prsg(prsg'HIGH-1 DOWNTO 0) & '0';
      -- PRSG feedback
      v_feedback := '0';
      FOR I IN c_common_lfsr_max_nof_feedbacks-1 DOWNTO 0 LOOP
        IF c_common_lfsr_sequences(c_lfsr_nr)(I) /= 0 THEN
          v_feedback := v_feedback XOR prsg(c_common_lfsr_sequences(c_lfsr_nr)(I)-1);
        END IF;
      END LOOP;
      nxt_prsg(0) <= NOT v_feedback;
 
      -- COUNTER
      nxt_cntr <= INCR_UVEC(cntr, g_incr);
    END IF;
  END common_lfsr_nxt_seq;
 
  FUNCTION func_common_random(lfsr : STD_LOGIC_VECTOR) RETURN STD_LOGIC_VECTOR IS
    CONSTANT c_lfsr_nr  : NATURAL := lfsr'LENGTH - c_common_lfsr_first;
    VARIABLE v_nxt_lfsr : STD_LOGIC_VECTOR(lfsr'RANGE);
    VARIABLE v_feedback : STD_LOGIC;
  BEGIN
    -- shift
    v_nxt_lfsr := lfsr(lfsr'HIGH-1 DOWNTO 0) & '0';
    -- feedback
    v_feedback := '0';
    FOR I IN c_common_lfsr_max_nof_feedbacks-1 DOWNTO 0 LOOP
      IF c_common_lfsr_sequences(c_lfsr_nr)(I) /= 0 THEN
        v_feedback := v_feedback XOR lfsr(c_common_lfsr_sequences(c_lfsr_nr)(I)-1);
      END IF;
    END LOOP;
    v_nxt_lfsr(0) := NOT v_feedback;
    RETURN v_nxt_lfsr;
  END func_common_random;
 
END common_lfsr_sequences_pkg;