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[/] [open8_urisc/] [trunk/] [VHDL/] [sdlc_crc16_ccitt.vhd] - Blame information for rev 242

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1 191 jshamlet
-- Copyright (c)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 :  crc16_ccitt
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-- Description:  Implements the 16-bit CCITT CRC on byte-wide data. Logic
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--  equations were taken from Intel/Altera app note AN049.
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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      04/14/20 Code cleanup and revision section added
32 191 jshamlet
 
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library ieee;
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use ieee.std_logic_1164.all;
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library work;
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  use work.sdlc_serial_pkg.all;
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entity sdlc_crc16_ccitt is
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generic(
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  Poly_Init                  : std_logic_vector(15 downto 0) := x"0000";
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  Reset_Level                : std_logic := '1'
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);
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port(
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  Clock                      : in  std_logic;
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  Reset                      : in  std_logic;
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  --
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  Clear                      : in  std_logic;
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  Wr_En                      : in  std_logic;
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  Wr_Data                    : in  DATA_IN_TYPE;
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  --
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  CRC16_Valid                : out std_logic;
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  CRC16_Out                  : out CRC_OUT_TYPE
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);
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end entity;
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architecture behave of sdlc_crc16_ccitt is
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  signal Calc_En             : std_logic    := '0';
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  signal Buffer_En           : std_logic    := '0';
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  signal Data                : DATA_IN_TYPE := x"00";
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  signal Exr                 : DATA_IN_TYPE := x"00";
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  signal Reg                 : CRC_OUT_TYPE := x"0000";
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begin
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  Exr(0)                     <= Reg(0) xor Data(0);
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  Exr(1)                     <= Reg(1) xor Data(1);
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  Exr(2)                     <= Reg(2) xor Data(2);
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  Exr(3)                     <= Reg(3) xor Data(3);
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  Exr(4)                     <= Reg(4) xor Data(4);
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  Exr(5)                     <= Reg(5) xor Data(5);
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  Exr(6)                     <= Reg(6) xor Data(6);
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  Exr(7)                     <= Reg(7) xor Data(7);
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  CRC16_Calc: process( Clock, Reset )
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  begin
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    if( Reset = Reset_Level )then
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      Calc_En                <= '0';
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      Buffer_En              <= '0';
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      Data                   <= x"00";
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      Reg                    <= x"0000";
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      CRC16_Out              <= x"0000";
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      CRC16_Valid            <= '0';
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    elsif( rising_edge(Clock) )then
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      Calc_En                <= Wr_En;
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      if( Wr_En  = '1' )then
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        Data                 <= Wr_Data;
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      end if;
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      if( Calc_En = '1' )then
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        Reg(0)               <= Reg(8)  xor            Exr(4) xor Exr(0);
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        Reg(1)               <= Reg(9)  xor            Exr(5) xor Exr(1);
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        Reg(2)               <= Reg(10) xor            Exr(6) xor Exr(2);
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        Reg(3)               <= Reg(11) xor Exr(0) xor Exr(7) xor Exr(3);
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        Reg(4)               <= Reg(12) xor Exr(1)                      ;
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        Reg(5)               <= Reg(13) xor Exr(2)                      ;
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        Reg(6)               <= Reg(14) xor Exr(3)                      ;
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        Reg(7)               <= Reg(15) xor Exr(4)            xor Exr(0);
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        Reg(8)               <= Exr(0)  xor Exr(5)            xor Exr(1);
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        Reg(9)               <= Exr(1)  xor Exr(6)            xor Exr(2);
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        Reg(10)              <= Exr(2)  xor Exr(7)            xor Exr(3);
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        Reg(11)              <= Exr(3)                                  ;
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        Reg(12)              <= Exr(4)                        xor Exr(0);
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        Reg(13)              <= Exr(5)                        xor Exr(1);
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        Reg(14)              <= Exr(6)                        xor Exr(2);
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        Reg(15)              <= Exr(7)                        xor Exr(3);
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      end if;
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      if( Clear = '1' )then
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        Reg                  <= Poly_Init;
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      end if;
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      Buffer_En              <= Calc_En;
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      if( Buffer_En = '1' )then
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        CRC16_Out            <= Reg xor x"FFFF";
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      end if;
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      CRC16_Valid            <= Buffer_En;
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    end if;
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  end process;
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end architecture;

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