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[/] [System09/] [trunk/] [rtl/] [VHDL/] [divu32.vhd] - Blame information for rev 203

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1 130 dilbert57
--===========================================================================--
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--                                                                           --
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--                  Synthesizable unsigned 32 bit integer divider            --
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--                                                                           --
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--===========================================================================--
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--
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--  File name      : divu32.vhd
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--
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--  Entity name    : udiv32
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--
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--  Purpose        : Implements a 32 bit unsigned integer divider 
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--                  
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--  Dependencies   : ieee.std_logic_1164
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--                   ieee.numeric_std
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--                   ieee.std_logic_unsigned
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--
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--  Author         : John E. Kent
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--
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--  Email          : dilbert57@opencores.org      
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--
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--  Web            : http://opencores.org/project,system09
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--
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--  Registers      :
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--  0 Dividend  1st Byte MSB
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--  1           2nd Byte
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--  2           3rd Byte 
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--  3           4th Byte LSB
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--  4 Divisor   1st Byte MSB
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--  5           2nd Byte
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--  6           3rd Byte
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--  7           4th Byte LSB
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--  8 Result    1st Byte MSB
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--  9           2nd Byte
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-- 10           3rd Byte
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-- 11           4th byte LSB
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-- 12 Remainder 1st Byte MSB
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-- 13           2nd Byte
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-- 14           3rd Byte
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-- 15           4th byte LSB
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--
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--  32 bit unsigned binary division.
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--
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--  Write the most significant byte of the dividend at the 0th register first 
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--  down to the least significant byte of the divisor in the 7th register.
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--  Writing the least significant byte of the divisor will start the division.
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--
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--  The 32 bit division will take 32 clock cycles.
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--  There is no status register so the CPU must execute a software delay
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--  to wait 32 clock cycles after the least significant byte of the divisor 
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--  is written before reading the result of the division or the remainder.
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--
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--  The dividend and divisor input registers are read/writable
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--  The result and remainder output registers are read only.
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--  The result register holds the integer part of the result of the division.
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--  The remainder register holds the dividend modulo the divisor.
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--
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--  Copyright (C) 2012 - 2014 John Kent
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--
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--  This program is free software: you can redistribute it and/or modify
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--  it under the terms of the GNU General Public License as published by
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--  the Free Software Foundation, either version 3 of the License, or
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--  (at your option) any later version.
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--
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--  This program is distributed in the hope that it will be useful,
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--  but WITHOUT ANY WARRANTY; without even the implied warranty of
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--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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--  GNU General Public License for more details.
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--
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--  You should have received a copy of the GNU General Public License
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--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
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--
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--===========================================================================--
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--                                                                           --
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--                              Revision  History                            --
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--                                                                           --
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--===========================================================================--
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--
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-- Version Author        Date         Changes
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--
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-- 0.1     John Kent     2012-04-06    Initial version
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-- 0.2     John Kent     2014-05-07    Replaced Status register with 4 byte remainder
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--
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library ieee;
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  use ieee.std_logic_1164.all;
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  use ieee.numeric_std.all;
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  use ieee.std_logic_unsigned.all;
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--library unisim;
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--  use unisim.vcomponents.all;
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entity udiv32 is
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  port (
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    --
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    -- CPU Interface signals
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    --
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    clk      : in  std_logic;                     -- CPU Clock
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    rst      : in  std_logic;                     -- Reset input (active high)
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    cs       : in  std_logic;                     -- Chip Select
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    addr     : in  std_logic_vector(3 downto 0);  -- Register Select
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    rw       : in  std_logic;                     -- Read / Not Write
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    data_in  : in  std_logic_vector(7 downto 0);  -- Data Bus In 
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    data_out : out std_logic_vector(7 downto 0)  -- Data Bus Out
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    );
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end udiv32;
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--================== End of entity ==============================--
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-------------------------------------------------------------------
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-- Architecture for unsigned 32 bit integer divider interface
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-------------------------------------------------------------------
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architecture rtl of udiv32 is
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signal dividend      : std_logic_vector(31 downto 0) := (others => '0');
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signal divisor       : std_logic_vector(31 downto 0) := (others => '0');
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signal result        : std_logic_vector(31 downto 0) := (others => '0');
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signal count         : std_logic_vector( 4 downto 0) := (others => '0');
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signal start_flag    : std_logic := '0';
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signal finish_flag   : std_logic := '0';
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signal dividend_temp : std_logic_vector(64 downto 0);
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signal divisor_temp  : std_logic_vector(64 downto 0);
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begin
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--
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-- Write registers
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--
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udiv32_write : process( clk, rst, data_in, finish_flag )
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begin
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  if falling_edge( clk ) then
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    if rst = '1' then
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      dividend    <= (others=> '0');   -- reset the dividend to zero
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      divisor     <= (others=> '0');   -- reset the divisor to zero
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      start_flag  <= '0';                                        -- the default state is stopped
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    else
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      --
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      -- start bit is normally reset
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      --
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      start_flag <= '0';
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      --
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      -- write to registers
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      --
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      if (cs = '1') and (rw = '0') then
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        case addr is
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        when "0000" =>
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          dividend(31 downto 24) <= data_in;
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        when "0001" =>
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          dividend(23 downto 16) <= data_in;
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        when "0010" =>
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          dividend(15 downto  8) <= data_in;
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        when "0011" =>
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          dividend( 7 downto  0) <= data_in;
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        when "0100" =>
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          divisor(31 downto 24)  <= data_in;
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        when "0101" =>
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          divisor(23 downto 16)  <= data_in;
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        when "0110" =>
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          divisor(15 downto  8)  <= data_in;
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        when "0111" =>
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          divisor( 7 downto  0)  <= data_in;
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          --
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          -- writing the last byte of the divisor 
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                         -- should pulse the start flag high for one cycle 
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                         -- starting the division,
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          -- provided the previous division has finished
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          --
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                         if (finish_flag = '1') then
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                                start_flag <= '1';
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                         end if;
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        when others =>
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           null;
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        end case;
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      end if;
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    end if; -- rst
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  end if; -- clk
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end process;
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--
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-- Read registers
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--
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udiv32_read : process( addr, dividend, divisor, result, dividend_temp )
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begin
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  case addr is
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  when "0000" =>
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    data_out <= dividend(31 downto 24);
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  when "0001" =>
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    data_out <= dividend(23 downto 16);
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  when "0010" =>
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    data_out <= dividend(15 downto  8);
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  when "0011" =>
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    data_out <= dividend( 7 downto  0);
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  when "0100" =>
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    data_out <= divisor(31 downto 24);
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  when "0101" =>
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    data_out <= divisor(23 downto 16);
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  when "0110" =>
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    data_out <= divisor(15 downto  8);
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  when "0111" =>
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    data_out <= divisor( 7 downto  0);
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  when "1000" =>
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    data_out <= result(31 downto 24);
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  when "1001" =>
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    data_out <= result(23 downto 16);
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  when "1010" =>
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    data_out <= result(15 downto  8);
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  when "1011" =>
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    data_out <= result( 7 downto  0);
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  when "1100" =>
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    data_out <= dividend_temp(31 downto 24);
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  when "1101" =>
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    data_out <= dividend_temp(23 downto 16);
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  when "1110" =>
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    data_out <= dividend_temp(15 downto  8);
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  when "1111" =>
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    data_out <= dividend_temp( 7 downto  0);
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  when others =>
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    null;
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  end case;
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end process;
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--
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-- When the finish flag is high and the start flag goes high, 
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-- start the division by clearing the finish flag
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-- When the finish flag is low and the count reaches 31 
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udiv32_divide : process( rst, clk, start_flag, finish_flag )
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variable result_temp    : std_logic_vector(64 downto 0);
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begin
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  if falling_edge( clk ) then
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    if (rst = '1') then
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      dividend_temp  <= (others=>'0');
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      divisor_temp   <= (others=>'0');
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      result_temp    := (others=>'0');
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      result         <= (others=>'0');
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      count          <= (others=>'0');
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      finish_flag    <= '1';             -- default state is finished
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    else
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      --
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      -- start the division if the last division was complete
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                -- i.e. the finish flag was set
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      -- and the last byte of the divisor was just written
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      -- i.e. the start flag was pulsed high for one clock cycle
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                --
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      if (start_flag = '1') and (finish_flag = '1') then
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        dividend_temp(64)           <= '0';                    -- dividend carry bit
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        dividend_temp(63 downto 32) <= (others => '0');        -- zero MSW
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        dividend_temp(31 downto  0) <= dividend(31 downto 0);  -- Mantissa in the bottom
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        divisor_temp(64)            <= '0';                    -- divisor carry bit
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        divisor_temp(63)            <= '0';                    -- 
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        divisor_temp(62 downto 31)  <= divisor(31 downto 0);   -- divisor starts off one bit down in MSW
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        divisor_temp(30 downto  0)  <= (others => '0');        -- bottom of divisor is zero
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        result_temp                 := (others => '0');        -- clear the result variable
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        count                       <= (others => '0');        -- zero the bit counter
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        finish_flag                 <= '0';                    -- flag that the division is in progress
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      elsif ( finish_flag = '0' ) then                         -- if finish flag is clear the division must be in progress
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        result_temp   := dividend_temp - divisor_temp;         -- subtract the divisor from the dividend
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        if result_temp(64) = '0' then                          -- if the result carry is clear
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          dividend_temp <= result_temp;                        -- update the dividend variable with the result variable
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        end if;
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        --
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        -- shift divisor down one bit
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        --
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        divisor_temp(62 downto 0) <= divisor_temp(63 downto 1);
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        --
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        -- shift the result up one bit
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        -- The LSBit is the inverted result carry
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        --
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        result(0)           <= not result_temp(64);
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        result(31 downto 1) <= result(30 downto 0);
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        --
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        -- 32 bit division should take 32 clock cycles
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        --
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        count               <= count + "00001";
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        --
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                  -- When the count reaches the 31st cycle of the division 
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        -- flag that the division is complete by setting the finish flag.
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        -- 
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        if count = "11111" then
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          finish_flag <= '1';  -- flag division complete
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        end if;
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      end if; -- start/finish
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    end if; -- rst
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  end if; -- clk
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end process;
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end rtl; -- end of architecture

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