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[/] [System09/] [trunk/] [rtl/] [VHDL/] [divs32_s2.vhd] - Blame information for rev 186

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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      : divs32.vhd
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--
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--  Entity name    : sdiv32
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--
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--  Purpose        : Implements a 32 bit signed 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 quotient    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 quotient 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 quotient and remainder output registers are read only.
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--  The quotient 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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-- 0.3     John Kent     2016-02-04    Shortend result_temp to 33 bits so subtraction is faster.
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--                                     Add hold output to pause CPU until result is valid.
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-- 0.4     John Kent     2018-03-21    Changed unsigned udiv32 to signed sdiv32
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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 sdiv32 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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         hold     : out std_logic                      -- Result access hold
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    );
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end sdiv32;
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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 sdiv32 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(63 downto 0) := (others => '0');
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signal quotient      : std_logic_vector(31 downto 0) := (others => '0');
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signal remainder     : 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 req_flag      : std_logic := '0';  -- Request Division
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signal act_flag      : std_logic := '0';  -- Division Active
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begin
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--
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-- Write registers
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--
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sdiv32_write : process( clk, rst, cs, rw, addr, data_in, req_flag, act_flag )
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begin
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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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      req_flag    <= '0';                                   -- the default state is stopped
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  elsif falling_edge( clk ) then
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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 request 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 (req_flag = '0') and (act_flag = '0') then
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                                req_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/clk
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  if (req_flag = '1') and (act_flag = '1') then
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    req_flag <= '0';
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  end if;
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  hold <= cs and rw and addr(3) and act_flag;
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end process;
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--
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-- Read registers
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--
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sdiv32_read : process( addr, dividend, divisor, quotient, remainder )
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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 <= quotient(31 downto 24);
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  when "1001" =>
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    data_out <= quotient(23 downto 16);
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  when "1010" =>
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    data_out <= quotient(15 downto  8);
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  when "1011" =>
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    data_out <= quotient( 7 downto  0);
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  when "1100" =>
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    data_out <= remainder(31 downto 24);
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  when "1101" =>
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    data_out <= remainder(23 downto 16);
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  when "1110" =>
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    data_out <= remainder(15 downto 8);
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  when "1111" =>
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    data_out <= remainder(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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sdiv32_divide : process( rst, clk, dividend, divisor, remainder, req_flag, act_flag, count )
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variable result_temp  : std_logic_vector(32 downto 0);
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begin
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    if (rst = '1') then
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           result          <= (others=>'0');
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                result_temp     := (others=>'0');
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      remainder       <= (others=>'0');
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      quotient        <= (others=>'0');
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      count           <= (others=>'0');
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      act_flag        <= '0';             -- default state is inactive
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    elsif falling_edge( clk ) then
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      --
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      -- activate the division if the last division was complete
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                -- i.e. the active flag was clear
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      -- and the last byte of the divisor was just written
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      -- i.e. the request flag was pulsed high for one clock cycle
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                --
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      if (req_flag = '1') and (act_flag = '0') then
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                  --
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                  -- put dividend in result and make positive
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                  --
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        result(63 downto 32) <= (others => '0');
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                  if dividend(31) = '0' then
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          result(31 downto  0) <= dividend;                 -- Dividend in the Least Significant Word of remainder
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                  else
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                    result(31 downto  0) <= "00000000000000000000000000000000" - dividend;
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                  end if;
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                  --
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                  -- Initialize temp variables
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                  --
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        result_temp        := (others => '0');            -- Clear the remainder temp variable
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                  --
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                  -- reset bit counter and activate division
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                  --
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        count              <= (others => '0');            -- Clear the bit counter
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        act_flag           <= '1';                        -- Flag division in progress
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      elsif (req_flag = '0') and (act_flag = '1') then                              -- If active flag is set the division must be in progress
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                  --
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                  -- if dividend positive, subrtact divisor
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                  -- if dividend negative, add divisor
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                  --
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        if (divisor(31)) = '0' then
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          result_temp := result(63 downto 31) - (divisor(31) & divisor);   -- subtract the divisor from the remainder if positive
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        else
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          result_temp := result(63 downto 31) + (divisor(31) & divisor);   -- add the divisor to the remainder if negative
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        end if;
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                  --
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                  -- if carry clear from add or subract
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                  -- update the remainder
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                  --
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        if result_temp(32) = '0' then                          -- if the remainder temp carry is clear
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          result(63 downto 32) <= result_temp(31 downto 0);    -- update the result with remainder
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        else
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          result(63 downto 32) <= result(62 downto 31);        -- otherwise shift remainder up one bit
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                  end if;
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        --
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        -- shift the quotient up one bit
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        -- The LSBit is the inverted remainder carry
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        --
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        result(31 downto  1) <= result(30 downto 0);        -- shift lower remainder up one bit
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                  result(0) <= not result_temp(32);                   -- shift quotient in bottom of remainder
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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 clrearing the active flag.
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        -- 
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        if count = "11111" then
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          act_flag <= '0';  -- flag division complete
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        end if;
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      end if; -- start/finish
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                --
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                -- negating the result will take another clock cycle.
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                -- If the cpu is held on a read access of the
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                -- quotient or remainder it may get the wrong result.
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                --
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310
                --
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                -- quotient has sign of dividend exclusive or divisor
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                --
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      if( (dividend(31) xor divisor(31)) = '0') then
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        quotient <= result(31 downto 0);
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      else
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        quotient <= "00000000000000000000000000000000" - result(31 downto 0);
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      end if;
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                --
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                -- remainder has sign of dividend
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                --
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                if dividend(31) = '0' then
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                  remainder <= result(63 downto 32);
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                else
325
                  remainder <= "00000000000000000000000000000000" - result(63 downto 32);
326
                end if;
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328
    end if; -- rst/clk
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end process;
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end rtl; -- end of architecture

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