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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_crc16_ccitt.vhd] - Blame information for rev 207

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1 180 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 : o8_crc16_ccitt
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-- Description: Implements the 16-bit CCITT CRC on byte-wide data suitable for
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--            :  use with the Open8 CPU. Logic equations were taken from
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--            :  Intel/Altera app note AN049.
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--
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-- Notes      :  Writing to the byte counter will reset all registers, and to
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--            :   should be used to clear the CRC accumulator/byte counter
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--            :   between frames.
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--
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-- Register Map:
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-- Offset  Bitfield Description                        Read/Write
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--   0x0   AAAAAAAA Data Input register (calc on write)(R/W)
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--   0x1   AAAAAAAA Byte Counter (clear all on write)  (R/W)
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--   0x2   AAAAAAAA B0 of calculated CRC               (RO)
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--   0x3   AAAAAAAA B1 of calculated CRC               (RO)
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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      12/19/19 Design Start
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library ieee;
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use ieee.std_logic_1164.all;
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use ieee.std_logic_unsigned.all;
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library work;
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  use work.open8_pkg.all;
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entity o8_crc16_ccitt is
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generic(
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  Reset_Level                : std_logic := '1';
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  Address                    : ADDRESS_TYPE
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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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  Bus_Address                : in  ADDRESS_TYPE;
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  Wr_Enable                  : in  std_logic;
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  Wr_Data                    : in  DATA_TYPE;
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  Rd_Enable                  : in  std_logic;
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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_crc16_ccitt is
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  constant Poly_Init         : std_logic_vector(15 downto 0) := x"0000";
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  constant User_Addr         : std_logic_vector(15 downto 2)
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                               := Address(15 downto 2);
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  alias  Comp_Addr           is Bus_Address(15 downto 2);
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  alias  Reg_Addr            is Bus_Address(1 downto 0);
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  signal Reg_Sel             : std_logic_vector(1 downto 0);
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  signal Addr_Match          : std_logic;
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  signal Wr_En               : std_logic;
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  signal Wr_Data_q           : DATA_TYPE;
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  signal Rd_En               : std_logic;
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  signal Next_Byte           : DATA_TYPE;
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  signal Byte_Count          : DATA_TYPE;
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  signal Calc_En             : std_logic;
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  signal Buffer_En           : std_logic;
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  signal Data                : DATA_TYPE;
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  signal Exr                 : DATA_TYPE;
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  signal Reg                 : std_logic_vector(15 downto 0);
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  signal Comp_Data           : std_logic_vector(15 downto 0);
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begin
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  Addr_Match                 <= '1' when Comp_Addr = User_Addr else '0';
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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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      Reg_Sel                <= "00";
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      Wr_En                  <= '0';
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      Wr_Data_q              <= x"00";
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      Rd_En                  <= '0';
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      Rd_Data                <= OPEN8_NULLBUS;
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      Byte_Count             <= x"00";
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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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    elsif( rising_edge(Clock) )then
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      Reg_Sel                <= Reg_Addr;
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      Wr_En                  <= Addr_Match and Wr_Enable;
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      Wr_Data_q              <= Wr_Data;
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      if( Wr_En = '1' )then
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        case( Reg_Sel )is
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          when "00" => -- Load next byte
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            Data             <= Wr_Data_q;
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            Calc_En          <= '1';
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          when "01" => -- Clear accumulator and byte counter
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            Byte_Count       <= x"00";
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            Reg              <= Poly_Init;
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          when others => null;
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        end case;
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      end if;
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      Rd_En                  <= Addr_Match and Rd_Enable;
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      Rd_Data                <= OPEN8_NULLBUS;
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      if( Rd_En = '1' )then
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        case( Reg_Sel )is
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          when "00" => -- Read last byte
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            Rd_Data          <= Data;
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          when "01" => -- Read the byte counter
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            Rd_Data          <= Byte_Count;
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          when "10" => -- Read the lower byte of the calculated CRC
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            Rd_Data          <= Comp_Data(7 downto 0);
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          when "11" => -- Read the upper byte of the calculated CRC
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            Rd_Data          <= Comp_Data(15 downto 8);
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          when others => null;
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        end case;
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      end if;
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      Calc_En                <= '0';
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      Buffer_En              <= Calc_En;
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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( Buffer_En = '1' )then
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        Byte_Count           <= Byte_Count + 1;
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        Comp_Data            <= Reg xor x"FFFF";
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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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