Subversion Repositories mod_sim_exp

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----  autorun_ctrl                                                ---- 

----                                                              ---- 

----  This file is part of the                                    ----

----    Modular Simultaneous Exponentiation Core project          ---- 

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

----                                                              ---- 

----  Description                                                 ---- 

----     autorun control unit for a pipelined montgomery          ----

----     multiplier                                               ----

----                                                              ----

----  Dependencies: none                                          ----

----                                                              ----

----  Authors:                                                    ----

----      - Geoffrey Ottoy, DraMCo research group                 ----

----      - Jonas De Craene, JonasDC@opencores.org                ---- 

----                                                              ---- 

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----                                                              ---- 

---- Copyright (C) 2011 DraMCo research group 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.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

entity autorun_cntrl is

  port (

    clk              : in  std_logic;

    reset            : in  std_logic;

    start            : in  std_logic;

    done             : out  std_logic;

    op_sel           : out  std_logic_vector (1 downto 0);

    start_multiplier : out  std_logic;

    multiplier_done  : in  std_logic;

    read_buffer      : out  std_logic;

    buffer_din       : in  std_logic_vector (31 downto 0);

    buffer_empty     : in  std_logic

  );

end autorun_cntrl;

architecture Behavioral of autorun_cntrl is

  signal bit_counter_i    : integer range 0 to 15 := 0;

  signal bit_counter_0_i  : std_logic;

  signal bit_counter_15_i : std_logic;

  signal next_bit_i       : std_logic := '0';

  signal start_cycle_i     : std_logic := '0';

  signal start_cycle_del_i : std_logic;

  signal done_i    : std_logic;

  signal running_i : std_logic;

  signal start_multiplier_i     : std_logic;

  signal start_multiplier_del_i : std_logic;

  signal mult_done_del_i        : std_logic;

  signal e0_bit_i        : std_logic;

  signal e1_bit_i        : std_logic;

  signal e_bits_i        : std_logic_vector(1 downto 0);

  signal e_bits_0_i      : std_logic;

  signal cycle_counter_i : std_logic;

  signal op_sel_sel_i    : std_logic;

  signal op_sel_i        : std_logic_vector(1 downto 0);

  signal exponent_shift_i : std_logic_vector(31 downto 0);

  signal read_buffer_i    : std_logic;

  signal read_buffer_i_d  : std_logic;

begin

  done <= done_i;

  read_buffer <= read_buffer_i;

  -- generate the index to select a single bit from the two exponents

  SYNC_BIT_COUNTER : process (clk, reset)

  begin

    if reset = '1' then

      bit_counter_i <= 15;

    elsif rising_edge(clk) then

      if start = '1' then -- make sure we start @ bit 0

        bit_counter_i <= 15;

      elsif next_bit_i = '1' then -- count

        if bit_counter_i = 0 then

          bit_counter_i <= 15;

        else

          bit_counter_i <= bit_counter_i - 1;

        end if;

      end if;

    end if;

  end process SYNC_BIT_COUNTER;

  -- process that implements the shift register for the exponents

  -- more performant than former mux implementation

  EXP_SHIFTER : process (clk, reset)

  begin

    if reset = '1' then

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

    elsif rising_edge(clk) then

      read_buffer_i_d <= read_buffer_i; -- delay read_buffer signal one clock

      if read_buffer_i_d = '1' then -- after new buffer read, shift in new bits

        exponent_shift_i <= buffer_din;

      elsif next_bit_i = '1' then -- count

        exponent_shift_i(31 downto 1) <= exponent_shift_i(30 downto 0);

      end if;

    end if;

  end process EXP_SHIFTER;

  -- signal when bit_counter_i = 0

  bit_counter_0_i <= '1' when bit_counter_i = 0 else '0';

  bit_counter_15_i <= '1' when bit_counter_i = 15 else '0';

  -- the bits...

  e0_bit_i <= exponent_shift_i(15);

  e1_bit_i <= exponent_shift_i(31);

  e_bits_i <= e0_bit_i & e1_bit_i;

  e_bits_0_i <= '1' when (e_bits_i = "00") else '0';

  -- operand pre-select

  with e_bits_i select

    op_sel_i <= "00" when "10", -- gt0

                "01" when "01", -- gt1

                "10" when "11", -- gt01

                "11" when others;

  -- select operands

  op_sel_sel_i <= '0' when e_bits_0_i = '1' else (cycle_counter_i);

  op_sel <= op_sel_i when op_sel_sel_i = '1' else "11";

  -- process that drives running_i signal ('1' when in autorun, '0' when not)

  RUNNING_PROC : process(clk, reset)

  begin

    if reset = '1' then

      running_i <= '0';

    elsif rising_edge(clk) then

      running_i <= start or (running_i and (not done_i));

    end if;

  end process RUNNING_PROC;

  -- ctrl logic

  start_multiplier_i <= start_cycle_del_i or (mult_done_del_i and (cycle_counter_i) and (not e_bits_0_i));

  read_buffer_i <= start_cycle_del_i and bit_counter_15_i and running_i; -- pop new word from fifo when bit_counter is back at '15'

  start_multiplier <= start_multiplier_del_i and running_i;

  -- start/stop logic

  start_cycle_i <= (start and (not buffer_empty)) or next_bit_i; -- start pulse (external or internal)

  done_i <= (start and buffer_empty) or (next_bit_i and bit_counter_0_i and buffer_empty); -- stop when buffer is empty

  next_bit_i <= (mult_done_del_i and e_bits_0_i) or (mult_done_del_i and (not e_bits_0_i) and (not cycle_counter_i));

  -- process for delaying signals with 1 clock cycle

  DEL_PROC : process(clk)

  begin

    if rising_edge(clk) then

      start_multiplier_del_i <= start_multiplier_i;

      start_cycle_del_i <= start_cycle_i;

      mult_done_del_i <= multiplier_done;

    end if;

  end process DEL_PROC;

  -- process for cycle counter

  CYCLE_CNTR_PROC : process(clk, start, reset)

  begin

    if start = '1' or reset = '1' then

      cycle_counter_i <= '0';

    elsif rising_edge(clk) then

      if (e_bits_0_i = '0') and (multiplier_done = '1') then

        cycle_counter_i <= not cycle_counter_i;

      elsif (e_bits_0_i = '1') and (multiplier_done = '1') then

        cycle_counter_i <= '0';

      else

        cycle_counter_i <= cycle_counter_i;

      end if;

    end if;

  end process CYCLE_CNTR_PROC;

end Behavioral;