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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_lfsr32.vhd] - Blame information for rev 309

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1 214 jshamlet
-- Copyright (c)2018, 2020 Jeremy Seth Henry
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-- All rights reserved.
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--
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-- Redistribution and use in source and binary forms, with or without
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-- modification, are permitted provided that the following conditions are met:
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--     * Redistributions of source code must retain the above copyright
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--       notice, this list of conditions and the following disclaimer.
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--     * Redistributions in binary form must reproduce the above copyright
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--       notice, this list of conditions and the following disclaimer in the
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--       documentation and/or other materials provided with the distribution,
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--       where applicable (as part of a user interface, debugging port, etc.)
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--
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-- THIS SOFTWARE IS PROVIDED BY JEREMY SETH HENRY ``AS IS'' AND ANY
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-- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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-- WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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-- DISCLAIMED. IN NO EVENT SHALL JEREMY SETH HENRY BE LIABLE FOR ANY
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-- DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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-- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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-- LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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-- ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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-- THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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--
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-- VHDL Units :  o8_register
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-- Description:  Provides a byte of pseudo-random data on every read
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--
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-- Register Map:
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-- Offset  Bitfield Description                        Read/Write
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--   0x00  AAAAAAAA Data output                          (RW)
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--
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-- Revision History
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-- Author          Date     Change
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------------------ -------- ---------------------------------------------------
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-- Seth Henry      04/25/18 Design Start
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-- Seth Henry      04/10/20 Code cleanup and comments
36 224 jshamlet
-- Seth Henry      04/16/20 Modified to use Open8 bus record
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library ieee;
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  use ieee.std_logic_1164.all;
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  use ieee.std_logic_misc.all;
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library work;
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  use work.open8_pkg.all;
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entity o8_lfsr32 is
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generic(
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  Init_Seed                  : std_logic_vector(31 downto 0) := x"CAFEBABE";
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  Address                    : ADDRESS_TYPE
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);
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port(
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  Open8_Bus                  : in OPEN8_BUS_TYPE;
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  Rd_Data                    : out DATA_TYPE
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);
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end entity;
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architecture behave of o8_lfsr32 is
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  alias Clock                is Open8_Bus.Clock;
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  alias Reset                is Open8_Bus.Reset;
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  constant User_Addr         : std_logic_vector(15 downto 1)
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                               := Address(15 downto 1);
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  alias  Comp_Addr           is Open8_Bus.Address(15 downto 1);
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  signal Addr_Match          : std_logic := '0';
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  alias  Reg_Sel_d           is Open8_Bus.Address(0);
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  signal Reg_Sel_q           : std_logic := '0';
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  signal Rd_En_d             : std_logic := '0';
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  signal Rd_En_q             : std_logic := '0';
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  signal d0                  : std_logic := '0';
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  signal lfsr                : std_logic_vector(31 downto 0) := x"00000000";
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  signal lfsr_q              : std_logic_vector(31 downto 0) := x"00000000";
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begin
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  Addr_Match                 <= '1' when Comp_Addr = User_Addr else '0';
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  Rd_En_d                    <= Addr_Match and Open8_Bus.Rd_En;
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  d0                         <= lfsr(31) xnor lfsr(21) xnor lfsr(1) xnor lfsr(0);
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  lfsr_proc: process( Clock, Reset )
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  begin
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    if( Reset = Reset_Level )then
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      Reg_Sel_q              <= '0';
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      Rd_En_q                <= '0';
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      Rd_Data                <= x"00";
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      lfsr                   <= Init_Seed;
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      lfsr_q                 <= x"00000000";
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    elsif( rising_edge(Clock) )then
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      Reg_Sel_q              <= Reg_Sel_d;
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      Rd_En_q                <= Rd_En_d;
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      Rd_Data                <= OPEN8_NULLBUS;
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      if( Rd_En_q = '1' )then
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        Rd_Data              <= lfsr_q(31 downto 24);
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        lfsr_q               <= lfsr_q(23 downto 0) & x"00";
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        if( Reg_Sel_q = '1' )then
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          Rd_Data            <= lfsr_q(31) & "0000000";
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          lfsr_q             <= lfsr_q(30 downto 0) & '0';
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        end if;
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      end if;
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      if( or_reduce(lfsr_q) = '0' )then
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        lfsr_q               <= lfsr;
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        lfsr                 <= lfsr(30 downto 0) & d0;
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      end if;
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    end if;
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  end process;
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end architecture;

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