Subversion Repositories neorv32

-- #################################################################################################

-- # << NEORV32 - True Random Number Generator (TRNG) >>                                           #

-- # ********************************************************************************************* #

-- # This unit implements a true random number generator which uses an inverter chain as entropy   #

-- # source. The inverter chain is constructed as GARO (Galois Ring Oscillator) TRNG. The single   #

-- # inverters are connected via simple latches that are used to enbale/disable the TRNG. Also,    #

-- # these latches are used as additional delay element. By using unique enable signals for each   #

-- # latch, the synthesis tool cannot "optimize" one of the inverters out of the design. Further-  #

-- # more, the latches prevent the synthesis tool from detecting combinatorial loops.              #

-- # The output of the GARO is de-biased by a simple von Neuman random extractor and is further    #

-- # post-processed by a 16-bit LFSR for improved whitening.                                       #

-- #                                                                                               #

-- # Sources:                                                                                      #

-- #  - GARO: "Experimental Assessment of FIRO- and GARO-based Noise Sources for Digital TRNG      #

-- #    Designs on FPGAs" by Martin Schramm, Reiner Dojen and Michael Heigly, 2017                 #

-- #  - Latches for platform independence: "Extended Abstract: The Butterfly PUF Protecting IP     #

-- #    on every FPGA" by Sandeep S. Kumar, Jorge Guajardo, Roel Maesyz, Geert-Jan Schrijen and    #

-- #    Pim Tuyls, Philips Research Europe, 2008                                                   #

-- #  - Von Neumann De-Biasing: "Iterating Von Neumann's Post-Processing under Hardware            #

-- #    Constraints" by Vladimir Rozic, Bohan Yang, Wim Dehaene and Ingrid Verbauwhede, 2016       #

-- # ********************************************************************************************* #

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2020, Stephan Nolting. All rights reserved.                                     #

-- #                                                                                               #

-- # Redistribution and use in source and binary forms, with or without modification, are          #

-- # permitted provided that the following conditions are met:                                     #

-- #                                                                                               #

-- # 1. Redistributions of source code must retain the above copyright notice, this list of        #

-- #    conditions and the following disclaimer.                                                   #

-- #                                                                                               #

-- # 2. Redistributions in binary form must reproduce the above copyright notice, this list of     #

-- #    conditions and the following disclaimer in the documentation and/or other materials        #

-- #    provided with the distribution.                                                            #

-- #                                                                                               #

-- # 3. Neither the name of the copyright holder nor the names of its contributors may be used to  #

-- #    endorse or promote products derived from this software without specific prior written      #

-- #    permission.                                                                                #

-- #                                                                                               #

-- # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS   #

-- # OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF               #

-- # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE    #

-- # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,     #

-- # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE #

-- # GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED    #

-- # AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING     #

-- # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED  #

-- # OF THE POSSIBILITY OF SUCH DAMAGE.                                                            #

-- # ********************************************************************************************* #

-- # The NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #

-- #################################################################################################

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library neorv32;

use neorv32.neorv32_package.all;

entity neorv32_trng is

  port (

    -- host access --

    clk_i  : in  std_ulogic; -- global clock line

    addr_i : in  std_ulogic_vector(31 downto 0); -- address

    rden_i : in  std_ulogic; -- read enable

    wren_i : in  std_ulogic; -- write enable

    data_i : in  std_ulogic_vector(31 downto 0); -- data in

    data_o : out std_ulogic_vector(31 downto 0); -- data out

    ack_o  : out std_ulogic  -- transfer acknowledge

  );

end neorv32_trng;

architecture neorv32_trng_rtl of neorv32_trng is

  -- advanced configuration --------------------------------------------------------------------------------

  constant num_inv_c   : natural := 16; -- length of GARO inverter chain (default=16, max=16)

  constant lfsr_taps_c : std_ulogic_vector(15 downto 0) := "1101000000001000"; -- Fibonacci LFSR feedback taps

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

  -- control register bits --

  constant ctrl_taps_lsb_c  : natural :=  0; -- -/w: TAP 0 enable

  constant ctrl_taps_msb_c  : natural := 15; -- -/w: TAP 15 enable

  constant ctrl_en_c        : natural := 31; -- r/w: TRNG enable

  -- data register bits --

  constant ctrl_data_lsb_c  : natural :=  0; -- r/-: Random data bit 0

  constant ctrl_data_msb_c  : natural := 15; -- r/-: Random data bit 15

  constant ctrl_rnd_valid_c : natural := 31; -- r/-: Output byte valid

  -- IO space: module base address --

  constant hi_abb_c : natural := index_size_f(io_size_c)-1; -- high address boundary bit

  constant lo_abb_c : natural := index_size_f(trng_size_c); -- low address boundary bit

  -- access control --

  signal acc_en : std_ulogic; -- module access enable

  signal addr   : std_ulogic_vector(31 downto 0); -- access address

  signal wren   : std_ulogic; -- full word write enable

  signal rden   : std_ulogic; -- read enable

  -- random number generator --

  signal rnd_inv         : std_ulogic_vector(num_inv_c-1 downto 0); -- inverter chain

  signal rnd_enable_sreg : std_ulogic_vector(num_inv_c-1 downto 0); -- enable shift register

  signal rnd_enable      : std_ulogic;

  signal tap_config      : std_ulogic_vector(15 downto 0);

  signal rnd_sync        : std_ulogic_vector(02 downto 0); -- metastability filter & de-biasing

  signal ready_ff        : std_ulogic; -- new random data available

  signal rnd_sreg        : std_ulogic_vector(15 downto 0); -- sample shift reg

  signal rnd_cnt         : std_ulogic_vector(04 downto 0);

  signal new_sample      : std_ulogic; -- new output byte ready

  signal rnd_data        : std_ulogic_vector(15 downto 0); -- random data register (read-only)

  -- Randomness extractor (von Neumann De-Biasing) --

  signal db_state  : std_ulogic;

  signal db_enable : std_ulogic; -- valid data from de-biasing

  signal db_data   : std_ulogic; -- actual data from de-biasing

begin

  -- Access Control -------------------------------------------------------------------------

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

  acc_en <= '1' when (addr_i(hi_abb_c downto lo_abb_c) = trng_base_c(hi_abb_c downto lo_abb_c)) else '0';

  addr   <= trng_base_c(31 downto lo_abb_c) & addr_i(lo_abb_c-1 downto 2) & "00"; -- word aligned

  wren   <= acc_en and wren_i;

  rden   <= acc_en and rden_i;

  -- Read/Write Access ----------------------------------------------------------------------

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

  rw_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

      ack_o <= acc_en and (rden_i or wren_i);

      -- write access --

      if (wren = '1') then

        if (addr = trng_ctrl_addr_c) then

          tap_config <= data_i(tap_config'left downto 0);

          rnd_enable <= data_i(ctrl_en_c);

        end if;

      end if;

      -- read access --

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

      if (rden = '1') then

        if (addr = trng_ctrl_addr_c) then

          data_o(ctrl_taps_msb_c downto ctrl_taps_lsb_c) <= tap_config;

          data_o(ctrl_en_c) <= rnd_enable;

        else -- trng_data_addr_c

          data_o(ctrl_data_msb_c downto ctrl_data_lsb_c) <= rnd_data;

          data_o(ctrl_rnd_valid_c) <= ready_ff;

        end if;

      end if;

    end if;

  end process rw_access;

  -- True Random Generator ------------------------------------------------------------------

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

  entropy_source: process(rnd_enable_sreg, rnd_enable, rnd_inv, tap_config)

  begin

    for i in 0 to num_inv_c-1 loop

      if (rnd_enable = '0') then -- start with a defined state (latch reset)

        rnd_inv(i) <= '0';

      -- uniquely enable latches to prevent synthesis from removing chain elements

      elsif (rnd_enable_sreg(i) = '1') then -- latch enable

        -- here we have the inverter chain --

        if (i = num_inv_c-1) then -- left most inverter?

          if (tap_config(i) = '1') then

            rnd_inv(i) <= not rnd_inv(0); -- direct input of right most inverter (= output signal)

          else

            rnd_inv(i) <= '0';

          end if;

        else

          if (tap_config(i) = '1') then

            rnd_inv(i) <= not (rnd_inv(i+1) xor rnd_inv(0)); -- use final output as feedback

          else

            rnd_inv(i) <= not rnd_inv(i+1); -- normal chain: use previous inverter's output as input

          end if;

        end if;

      end if;

    end loop; -- i

  end process entropy_source;

  -- unique enable signals for each inverter latch --

  inv_enable: process(clk_i)

  begin

    if rising_edge(clk_i) then

      -- using individual enable signals for each inverter - derived from a shift register - to prevent the synthesis tool

      -- from removing all but one inverter (since they implement "logical identical functions")

      -- this also allows to make the trng platform independent

      rnd_enable_sreg <= rnd_enable_sreg(num_inv_c-2 downto 0) & rnd_enable; -- activate right most inverter first

    end if;

  end process inv_enable;

  -- Processing Core ------------------------------------------------------------------------

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

  processing_core: process(clk_i)

  begin

    if rising_edge(clk_i) then

      -- synchronize output of GARO --

      rnd_sync <= rnd_sync(1 downto 0) & rnd_inv(0); -- no more metastability

      -- von Neumann De-Biasing state --

      db_state <= (not db_state) and rnd_enable; -- just toggle -> process in every second cycle

      -- sample random data & post-processing --

      if (rnd_enable = '0') then

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

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

      elsif (db_enable = '1') then -- valid de-biased output?

        if (rnd_cnt = "10000") then

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

        else

          rnd_cnt <= std_ulogic_vector(unsigned(rnd_cnt) + 1);

        end if;

        rnd_sreg <= rnd_sreg(rnd_sreg'left-1 downto 0) & (xnor_all_f(rnd_sreg and lfsr_taps_c) xor db_data); -- LFSR post-processing

--      rnd_sreg <= rnd_sreg(rnd_sreg'left-1 downto 0) & db_data; -- LFSR post-processing

      end if;

      -- data output register --

      if (new_sample = '1') then

        rnd_data <= rnd_sreg;

      end if;

      -- data ready flag --

      if (rnd_enable = '0') or (rden = '1') then -- clear when deactivated or on data read

        ready_ff <= '0';

      elsif (new_sample = '1') then

        ready_ff <= '1';

      end if;

    end if;

  end process processing_core;

  -- John von Neumann De-Biasing --

  debiasing: process(db_state, rnd_sync)

    variable tmp_v : std_ulogic_vector(2 downto 0);

  begin

    -- check groups of two non-overlapping bits from the input stream

    tmp_v := db_state & rnd_sync(2 downto 1);

    case tmp_v is

      when "101"  => db_enable <= '1'; db_data <= '1'; -- rising edge  -> '1'

      when "110"  => db_enable <= '1'; db_data <= '0'; -- falling edge -> '0'

      when others => db_enable <= '0'; db_data <= '0'; -- invalid

    end case;

  end process debiasing;

  -- new valid byte available? --

  new_sample <= '1' when (rnd_cnt = "10000") and (rnd_enable = '1') and (db_enable = '1') else '0';

end neorv32_trng_rtl;