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

-- TITLE: Multiplication and Division Unit

-- AUTHOR: Steve Rhoads (rhoadss@yahoo.com)

-- DATE CREATED: 1/31/01

-- FILENAME: mult.vhd

-- PROJECT: MIPS CPU core

-- COPYRIGHT: Software placed into the public domain by the author.

--    Software 'as is' without warranty.  Author liable for nothing.

-- DESCRIPTION:

--    Implements the multiplication and division unit.

--    Normally takes 32 clock cycles.

--    if b(31 downto 16) = ZERO(31 downto 16) then mult in 16 cycles. 

--    if b(31 downto 8) = ZERO(31 downto 8) then mult in 8 cycles. 

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

library ieee;

use ieee.std_logic_1164.all;

use work.mips_pack.all;

entity mult is

   port(clk       : in std_logic;

        a, b      : in std_logic_vector(31 downto 0);

        mult_func : in mult_function_type;

        c_mult    : out std_logic_vector(31 downto 0);

        pause_out : out std_logic);

end; --entity mult

architecture logic of mult is

--   type mult_function_type is (

--      mult_nothing, mult_read_lo, mult_read_hi, mult_write_lo, 

--      mult_write_hi, mult_mult, mult_divide, mult_signed_divide);

   signal do_div_reg    : std_logic;

   signal do_signed_reg : std_logic;

   signal count_reg     : std_logic_vector(5 downto 0);

   signal reg_a         : std_logic_vector(31 downto 0);

   signal reg_b         : std_logic_vector(63 downto 0);

   signal answer_reg    : std_logic_vector(31 downto 0);

begin

--multiplication/division unit

mult_proc: process(clk, a, b, mult_func,

                   do_div_reg, do_signed_reg, count_reg,

                   reg_a, reg_b, answer_reg)

   variable do_div_temp    : std_logic;

   variable do_signed_temp : std_logic;

   variable count_temp     : std_logic_vector(5 downto 0);

   variable a_temp         : std_logic_vector(31 downto 0);

   variable b_temp         : std_logic_vector(63 downto 0);

   variable answer_temp    : std_logic_vector(31 downto 0);

   variable sign_extension : std_logic;

   variable aa, bb         : std_logic_vector(32 downto 0);

   variable sum            : std_logic_vector(32 downto 0);

   variable start          : std_logic;

   variable do_write       : std_logic;

   variable do_hi          : std_logic;

begin

   do_div_temp    := do_div_reg;

   do_signed_temp := do_signed_reg;

   count_temp     := count_reg;

   a_temp         := reg_a;

   b_temp         := reg_b;

   answer_temp    := answer_reg;

   sign_extension := '0';

   aa             := '0' & ZERO;

   bb             := '0' & ZERO;

   sum            := '0' & ZERO;

   start          := '0';

   do_write       := '0';

   do_hi          := '0';

   case mult_func is

   when mult_read_lo =>

   when mult_read_hi =>

      do_hi := '1';

   when mult_write_lo =>

      do_write := '1';

   when mult_write_hi =>

      do_write := '1';

      do_hi := '1';

   when mult_mult =>

      start := '1';

      do_div_temp := '0';

   when mult_divide =>

      start := '1';

      do_div_temp := '1';

      do_signed_temp := '0';

   when mult_signed_divide =>

      start := '1';

      do_div_temp := '1';

      do_signed_temp := '1';

   when others =>

   end case;

   if start = '1' then

      count_temp := "000000";

      a_temp := a;

      answer_temp := ZERO;

      if do_div_temp = '1' then

         if do_signed_temp = '0' or b(31) = '0' then

            b_temp(62 downto 31) := b;

         else

            b_temp(62 downto 31) := bv_negate(b);

            a_temp := bv_negate(a);

         end if;

         b_temp(30 downto 0) := ZERO(30 downto 0);

      else --multiply

         b_temp := ZERO & b;

      end if;

   elsif do_write = '1' then

      if do_hi = '0' then

         b_temp(31 downto 0) := a;

      else

         b_temp(63 downto 32) := a;

      end if;

   end if;

   if do_div_reg = '1' then

      bb := reg_b(32 downto 0);

   else

      bb := '0' & reg_b(63 downto 32);

   end if;

   sign_extension := reg_a(31) and do_signed_reg;

   aa := sign_extension & reg_a;

   sum := bv_adder(aa, bb, do_div_reg);

--   sum := bv_adder_lookahead(aa, bb, do_div_reg);

   if count_reg(5) = '0' and start = '0' then

      count_temp := bv_inc6(count_reg);

      if do_div_reg = '1' then

         answer_temp(31 downto 1) := answer_reg(30 downto 0);

         if reg_b(63 downto 32) = ZERO and sum(32) = '0' then

            a_temp := sum(31 downto 0);  --aa=aa-bb;

            answer_temp(0) := '1';

         else

            answer_temp(0) := '0';

         end if;

         if count_reg /= "011111" then

            b_temp(62 downto 0) := reg_b(63 downto 1);

         else

            b_temp(63 downto 32) := a_temp;

            b_temp(31 downto 0) := answer_temp;

         end if;

      else  -- mult_mode

         if reg_b(0) = '1' then

            b_temp(63 downto 31) := sum;

         else

            b_temp(63 downto 31) := '0' & reg_b(63 downto 32);

         end if;

         b_temp(30 downto 0) := reg_b(31 downto 1);

         if count_reg = "010000" and          --early stop

               reg_b(15 downto 0) = ZERO(15 downto 0) then

            count_temp := "111111";

            b_temp(31 downto 0) := reg_b(47 downto 16);

         end if;

         if count_reg = "001000" and          --early stop

               reg_b(23 downto 0) = ZERO(23 downto 0) then

            count_temp := "111111";

            b_temp(31 downto 0) := reg_b(55 downto 24);

         end if;

      end if;

   end if;

   if rising_edge(clk) then

      do_div_reg <= do_div_temp;

      do_signed_reg <= do_signed_temp;

      count_reg <= count_temp;

      reg_a <= a_temp;

      reg_b <= b_temp;

      answer_reg <= answer_temp;

   end if;

   if count_reg(5) = '0' and mult_func/= mult_nothing and start = '0' then

      pause_out <= '1';

   else

      pause_out <= '0';

   end if;

   if mult_func = mult_read_lo then

      c_mult <= reg_b(31 downto 0);

   elsif mult_func = mult_read_hi then

      c_mult <= reg_b(63 downto 32);

   else

      c_mult <= ZERO;

   end if;

end process;

end; --architecture logic