Subversion Repositories yahamm

-------------------------------------------------------------------------------

-- Yahamm IP core

--

-- This file is part of the Yahamm project

-- http://www.opencores.org/cores/yahamm

--

-- Description

-- A hamming encoder and decoder with single-error correcting and

-- double-error detecting capability. The message length can be configured

-- through a generic. Both the code generator matrix and the parity-check

-- matrix are computed in the VHDL itself.

--

-- To Do:

-- - write docs

--

-- Author:

-- - Nicola De Simone, ndesimone@opencores.org

--

-------------------------------------------------------------------------------

--

-- Copyright (C) 2017 Authors and OPENCORES.ORG

--

-- This source file may be used and distributed without

-- restriction provided that this copyright statement is not

-- removed from the file and that any derivative work contains

-- the original copyright notice and the associated disclaimer.

--

-- This source file is free software; you can redistribute it

-- and/or modify it under the terms of the GNU Lesser General

-- Public License as published by the Free Software Foundation;

-- either version 2.1 of the License, or (at your option) any

-- later version.

--

-- This source 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 Lesser General Public License for more

-- details.

--

--- You should have received a copy of the GNU Lesser General

-- Public License along with this source; if not, download it

-- from http://www.opencores.org/lgpl.shtml

--

-------------------------------------------------------------------------------

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library yahamm;

use yahamm.matrix_pkg.all;

use yahamm.yahamm_pkg.all;

library std;

use std.textio.all;

-- There are two monitor counters:

--

-- cnt_errors_corrected: number of error correction performed.

-- cnt_errors_detected: numbers of errors detected but not corrected.

--

-- The two never count together and they don't overflow.  If CORRECT

-- is false, no correction is performed cnt_errors_corrected never counts.

-- If CORRECT is true and EXTRA_PARITY_BIT is true, cnt_errors_detected

-- never counts because all errors (supposedly single-bit errors) are

-- corrected.

--

-- ERROR_LEN: width of the cnt_errors_corrected and cnt_errors_detected counters.

--

-- dout_valid_o: dout data valid, it's the en input pipelined.  It takes into

-- account the total latency.

--

entity yahamm_dec is

  generic (

    MESSAGE_LENGTH       : natural := 5;

    CORRECT : boolean := true;

    EXTRA_PARITY_BIT : natural range 0 to 1 := 1;

    ONE_PARITY_BIT : boolean := false;

    ERROR_LEN : natural := 16

    );

  port(

    clk_i, rst_i : in  std_logic;

    cnt_clr_i : in std_logic := '0';             -- Clear monitor counters.

    en_i       : in  std_logic := '1';          -- Input enable.

    data_i        : in  std_logic_vector(MESSAGE_LENGTH - 1 downto 0);  -- Input data.

    parity_i   : in std_logic_vector(calc_nparity_bits(MESSAGE_LENGTH, ONE_PARITY_BIT) + EXTRA_PARITY_BIT - 1 downto 0);    -- Parity bits.

    data_o        : out std_logic_vector(MESSAGE_LENGTH - 1 downto 0);  -- Out data.

    dout_valid_o : out std_logic;                                          -- data_o valid.

    cnt_errors_corrected_o, cnt_errors_detected_o : out std_logic_vector(ERROR_LEN - 1 downto 0);

    log_wrong_bit_pos_data_o : out std_logic_vector(MESSAGE_LENGTH - 1 downto 0);

    log_wrong_bit_pos_parity_o : out std_logic_vector(calc_nparity_bits(MESSAGE_LENGTH, ONE_PARITY_BIT) + EXTRA_PARITY_BIT - 1 downto 0)

    );

end yahamm_dec;

architecture std of yahamm_dec is

  constant NPARITY_BITS : natural := calc_nparity_bits(MESSAGE_LENGTH, ONE_PARITY_BIT);

  constant BLOCK_LENGTH : natural := calc_block_length(MESSAGE_LENGTH, ONE_PARITY_BIT);

  constant H : matrix_t(0 to NPARITY_BITS + EXTRA_PARITY_BIT - 1,

    get_parity_check_matrix(MESSAGE_LENGTH, EXTRA_PARITY_BIT, ONE_PARITY_BIT);

  signal data_i_padded : bit_vector(BLOCK_LENGTH - NPARITY_BITS - 1 downto 0);

  signal code_sys, code_nonsys, code_nonsys_q : bit_vector(BLOCK_LENGTH + EXTRA_PARITY_BIT - 1 downto 0);

  signal syndrome : bit_vector(NPARITY_BITS + EXTRA_PARITY_BIT - 1 downto 0);

  signal wrong_bit : integer range 0 to code_sys'length;

  constant SWAPM : matrix_t(0 to BLOCK_LENGTH + EXTRA_PARITY_BIT - 1,

    get_form_swap_matrix(MESSAGE_LENGTH, EXTRA_PARITY_BIT, ONE_PARITY_BIT);

  signal correction_en : boolean;

  signal cnt_errors_corrected_o_int, cnt_errors_detected_o_int : unsigned(ERROR_LEN - 1 downto 0);

  signal log_wrong_bit_pos_data_o_sys, log_wrong_bit_pos_data_o_nonsys : bit_vector(BLOCK_LENGTH + EXTRA_PARITY_BIT - 1 downto 0);

  signal dout_valid_o_p0 : std_logic;

begin

  check_parameters(BLOCK_LENGTH, NPARITY_BITS, MESSAGE_LENGTH, EXTRA_PARITY_BIT, ONE_PARITY_BIT, CORRECT);

  cnt_errors_corrected_o <= std_logic_vector(cnt_errors_corrected_o_int);

  cnt_errors_detected_o <= std_logic_vector(cnt_errors_detected_o_int);

  -- Pad data_i with zeros on the left, so that data_i_padded'length = BLOCK_LENGTH.

  -- This allow the user to reduce data_i width.

  data_i_padded(MESSAGE_LENGTH - 1 downto 0) <= to_bitvector(data_i);

  gen_padding: if BLOCK_LENGTH - NPARITY_BITS > MESSAGE_LENGTH generate

    data_i_padded(BLOCK_LENGTH - NPARITY_BITS - 1 downto MESSAGE_LENGTH) <= (others => '0');

  end generate gen_padding;

  -- Wire data and parity inputs in the systematic code code_sys (data

  -- on LSB, parity on MSB).

  code_sys <= to_bitvector(parity_i) & data_i_padded;

  -- Get the non-systematic code code_nonsys by swapping the

  -- systematic code code_sys.  The non-systematic code is needed to

  -- obtain an immediately meaningful syndrome.  This is timing-safe:

  -- no logic here, it's purely wiring.

  code_nonsys <= xor_multiply_vec(SWAPM, code_sys);

  -- Output log_wrong_bit_pos_log, uses log_wrong_bit_pos_log_nonsys is padded

  -- as data_i_padded

  log_wrong_bit_pos_data_o_sys <= xor_multiply_vec(SWAPM, log_wrong_bit_pos_data_o_nonsys);

  log_wrong_bit_pos_data_o <= To_StdLogicVector(log_wrong_bit_pos_data_o_sys(MESSAGE_LENGTH-1 downto 0));

  log_wrong_bit_pos_parity_o <= To_StdLogicVector(log_wrong_bit_pos_data_o_sys(BLOCK_LENGTH + EXTRA_PARITY_BIT - 1 downto BLOCK_LENGTH - NPARITY_BITS));

  -- purpose: Compute error syndrome from the non-systematic code

  -- (input) and the non-systemacic parity check matrix H.  Also delay

  -- code_nonsys to have code_nonsys_q synchronous with syndrome.  And start

  -- pipelining en input.

  -- type   : sequential

  -- inputs : clk_i, rst_i, code_nonsys

  -- outputs: syndrome

  syndrome_proc: process (clk_i, rst_i) is

  begin  -- process syndrome_proc

    if rst_i = '1' then                   -- asynchronous reset (active high)

      syndrome <= (others => '0');

      code_nonsys_q <= (others => '0');

      dout_valid_o_p0 <= '0';

    elsif rising_edge(clk_i) then         -- rising clock edge

      syndrome <= xor_multiply_vec(H, code_nonsys);

      code_nonsys_q <= code_nonsys;

      dout_valid_o_p0 <= en_i;

    end if;

  end process syndrome_proc;

  -- purpose: Enable error correction (signal correction_en) for a single bit

  -- error.  Dependent from the generic parameters.  If correction is enabled

  -- wrong_bit signal is assigned the position of the wrong bit.

  -- type   : combinational

  -- inputs : syndrome

  -- outputs: correction_enabled

  correction_enable_proc: process (syndrome) is

  begin  -- process correction_enable_proc

    wrong_bit <= 0;

    case CORRECT is

      when false =>

        -- Entity does not implement correction.                

        correction_en <= false;

      when true =>

        -- Entity implements correction.

        case EXTRA_PARITY_BIT is

          when 0 =>

            -- SEC case (see table).  Always correct.            

            correction_en <= true;

            -- The wrong bit is the syndrome itself.

            wrong_bit <= to_integer(unsigned(To_StdULogicVector(syndrome)));

          when 1 =>

            -- SECDED case (see table).  The error, if any, is a single error to be

            -- corrected if the extra parity bit in the syndrome is '1'.

            if syndrome(syndrome'high) = '0' then

              -- Double error: don't correct.

              correction_en <= false;

            else

              -- Single error: correct.        

              correction_en <= true;

              -- The wrong bit is not just the syndrome, because the

              -- syndrome has the extra parity bit as MSB bit.

              if or_reduce(syndrome(syndrome'high-1 downto 0)) = '0' then

                -- No other error.  So the extra parity bit itself is

                -- wrong, that in this implementation is the MSB of

                -- the non-systematic code word.

                wrong_bit <= code_nonsys_q'length;

              else

                -- Extra parity bit '1', ignore it for wrong_bit position.

                wrong_bit <= to_integer(unsigned(To_StdULogicVector(syndrome(NPARITY_BITS-1 downto 0))));

              end if;

            end if;

        end case;

    end case;

  end process correction_enable_proc;

  -- purpose: Decode the non systematic code code_nonsys_q and drive

  -- output data_o.  Single error correction is performed, depending on

  -- the configuration.

  -- type   : sequential

  -- inputs : clk_i, rst_i, code_nonsys_q, syndrome

  -- outputs: data_o

  decode_proc: process (clk_i, rst_i) is

    variable iserror : boolean;         -- parity error condition

    variable code_sys_dec, code_nonsys_dec : bit_vector(code_sys'range);

  begin  -- process decode_proc

    if rst_i = '1' then                   -- asynchronous reset (active high)

      data_o <= (others => '0');

      dout_valid_o <= '0';

    elsif rising_edge(clk_i) then         -- rising clock edge

      if dout_valid_o_p0 = '0' then

        data_o <= (others => '0');

        dout_valid_o <= '0';

      else

        code_nonsys_dec := code_nonsys_q;

        iserror := or_reduce(syndrome) = '1';

        if correction_en and iserror then

          code_nonsys_dec(wrong_bit-1) := not code_nonsys_q(wrong_bit-1);

        end if;

        code_sys_dec := xor_multiply_vec(SWAPM, code_nonsys_dec);

        data_o <= To_StdLogicVector(code_sys_dec(MESSAGE_LENGTH - 1 downto 0));

        dout_valid_o <= '1';

      end if;

    end if;

  end process decode_proc;

  -- purpose: Monitor counters.

  -- type   : sequential

  -- inputs : clk_i, rst_i, syndrome, correction_en

  -- outputs: cnt_errors_corrected_o_int, cnt_errors_detected_o_int, log_wrong_bit_pos_log

  cnt_proc: process (clk_i, rst_i) is

    variable iserror : boolean;         -- parity error condition

  begin  -- process cnt_proc

    if rst_i = '1' then                   -- asynchronous reset (active high)

      cnt_errors_detected_o_int <= (others => '0');

      cnt_errors_corrected_o_int <= (others => '0');

    elsif rising_edge(clk_i) then         -- rising clock edge

      if cnt_clr_i = '1' then

        -- synchronous clear

        cnt_errors_detected_o_int <= (others => '0');

        cnt_errors_corrected_o_int <= (others => '0');

      else

        iserror := or_reduce(syndrome) = '1';

        if iserror then

          if correction_en then

            if and_reduce(to_bitvector(std_logic_vector(cnt_errors_corrected_o_int))) /= '1' then

              cnt_errors_corrected_o_int <= cnt_errors_corrected_o_int + 1;

            end if;

          else

            if and_reduce(to_bitvector(std_logic_vector(cnt_errors_detected_o_int))) /= '1' then

              cnt_errors_detected_o_int <= cnt_errors_detected_o_int + 1;

            end if;

          end if;

        end if;

      end if;

    end if;

  end process cnt_proc;

  -- purpose: Monitor counters.

  -- type   : sequential

  -- inputs : clk_i, rst_i, syndrome, correction_en

  -- outputs: cnt_errors_corrected_o_int, cnt_errors_detected_o_int, log_wrong_bit_pos_log

  log_wrong_bit_gen: if CORRECT generate

    log_wrong_bit_proc: process (clk_i, rst_i) is

      variable iserror : boolean;         -- parity error condition

    begin  -- process cnt_proc

      if rst_i = '1' then

        log_wrong_bit_pos_data_o_nonsys <= (others => '0');

      elsif rising_edge(clk_i) then

        if cnt_clr_i = '1' then

          log_wrong_bit_pos_data_o_nonsys <= (others => '0');

        else

          iserror := or_reduce(syndrome) = '1';

          if iserror then

            if correction_en then

              -- Note: wrong_bit refers to the wrong bit of the code in

              -- non-systematic form.  Indeed this is swapped to

              -- systematic form for the output.

              log_wrong_bit_pos_data_o_nonsys(wrong_bit-1) <= '1';

            end if;

          end if;

        end if;

        end if;

      end process log_wrong_bit_proc;

    end generate log_wrong_bit_gen;

end architecture std;