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nn-usb-fpga/plasma/logic/mult.vhd
Carlos Camargo 22c469585b Adding plasma example
2010-04-21 20:01:38 -05:00

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7.2 KiB
VHDL
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---------------------------------------------------------------------
-- TITLE: Multiplication and Division Unit
-- AUTHORS: Steve Rhoads (rhoadss@yahoo.com)
-- DATE CREATED: 1/31/01
-- FILENAME: mult.vhd
-- PROJECT: Plasma 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 in 32 clocks.
--
-- To reduce space, compile your code using the flag "-mno-mul" which
-- will use software base routines in math.c if USE_SW_MULT is defined.
-- Then remove references to the entity mult in mlite_cpu.vhd.
--
-- MULTIPLICATION
-- long64 answer = 0
-- for(i = 0; i < 32; ++i)
-- {
-- answer = (answer >> 1) + (((b&1)?a:0) << 31);
-- b = b >> 1;
-- }
--
-- DIVISION
-- long upper=a, lower=0;
-- a = b << 31;
-- for(i = 0; i < 32; ++i)
-- {
-- lower = lower << 1;
-- if(upper >= a && a && b < 2)
-- {
-- upper = upper - a;
-- lower |= 1;
-- }
-- a = ((b&2) << 30) | (a >> 1);
-- b = b >> 1;
-- }
---------------------------------------------------------------------
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use IEEE.std_logic_arith.all;
use work.mlite_pack.all;
entity mult is
generic(mult_type : string := "DEFAULT");
port(clk : in std_logic;
reset_in : 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
constant MODE_MULT : std_logic := '1';
constant MODE_DIV : std_logic := '0';
signal mode_reg : std_logic;
signal negate_reg : std_logic;
signal sign_reg : std_logic;
signal sign2_reg : std_logic;
signal count_reg : std_logic_vector(5 downto 0);
signal aa_reg : std_logic_vector(31 downto 0);
signal bb_reg : std_logic_vector(31 downto 0);
signal upper_reg : std_logic_vector(31 downto 0);
signal lower_reg : std_logic_vector(31 downto 0);
signal a_neg : std_logic_vector(31 downto 0);
signal b_neg : std_logic_vector(31 downto 0);
signal sum : std_logic_vector(32 downto 0);
begin
-- Result
c_mult <= lower_reg when mult_func = MULT_READ_LO and negate_reg = '0' else
bv_negate(lower_reg) when mult_func = MULT_READ_LO
and negate_reg = '1' else
upper_reg when mult_func = MULT_READ_HI else
ZERO;
pause_out <= '1' when (count_reg /= "000000") and
(mult_func = MULT_READ_LO or mult_func = MULT_READ_HI) else '0';
-- ABS and remainder signals
a_neg <= bv_negate(a);
b_neg <= bv_negate(b);
sum <= bv_adder(upper_reg, aa_reg, mode_reg);
--multiplication/division unit
mult_proc: process(clk, reset_in, a, b, mult_func,
a_neg, b_neg, sum, sign_reg, mode_reg, negate_reg,
count_reg, aa_reg, bb_reg, upper_reg, lower_reg)
variable count : std_logic_vector(2 downto 0);
begin
count := "001";
if reset_in = '1' then
mode_reg <= '0';
negate_reg <= '0';
sign_reg <= '0';
sign2_reg <= '0';
count_reg <= "000000";
aa_reg <= ZERO;
bb_reg <= ZERO;
upper_reg <= ZERO;
lower_reg <= ZERO;
elsif rising_edge(clk) then
case mult_func is
when MULT_WRITE_LO =>
lower_reg <= a;
negate_reg <= '0';
when MULT_WRITE_HI =>
upper_reg <= a;
negate_reg <= '0';
when MULT_MULT =>
mode_reg <= MODE_MULT;
aa_reg <= a;
bb_reg <= b;
upper_reg <= ZERO;
count_reg <= "100000";
negate_reg <= '0';
sign_reg <= '0';
sign2_reg <= '0';
when MULT_SIGNED_MULT =>
mode_reg <= MODE_MULT;
if b(31) = '0' then
aa_reg <= a;
bb_reg <= b;
sign_reg <= a(31);
else
aa_reg <= a_neg;
bb_reg <= b_neg;
sign_reg <= a_neg(31);
end if;
sign2_reg <= '0';
upper_reg <= ZERO;
count_reg <= "100000";
negate_reg <= '0';
when MULT_DIVIDE =>
mode_reg <= MODE_DIV;
aa_reg <= b(0) & ZERO(30 downto 0);
bb_reg <= b;
upper_reg <= a;
count_reg <= "100000";
negate_reg <= '0';
when MULT_SIGNED_DIVIDE =>
mode_reg <= MODE_DIV;
if b(31) = '0' then
aa_reg(31) <= b(0);
bb_reg <= b;
else
aa_reg(31) <= b_neg(0);
bb_reg <= b_neg;
end if;
if a(31) = '0' then
upper_reg <= a;
else
upper_reg <= a_neg;
end if;
aa_reg(30 downto 0) <= ZERO(30 downto 0);
count_reg <= "100000";
negate_reg <= a(31) xor b(31);
when others =>
if count_reg /= "000000" then
if mode_reg = MODE_MULT then
-- Multiplication
if bb_reg(0) = '1' then
upper_reg <= (sign_reg xor sum(32)) & sum(31 downto 1);
lower_reg <= sum(0) & lower_reg(31 downto 1);
sign2_reg <= sign2_reg or sign_reg;
sign_reg <= '0';
bb_reg <= '0' & bb_reg(31 downto 1);
-- The following six lines are optional for speedup
--elsif bb_reg(3 downto 0) = "0000" and sign2_reg = '0' and
-- count_reg(5 downto 2) /= "0000" then
-- upper_reg <= "0000" & upper_reg(31 downto 4);
-- lower_reg <= upper_reg(3 downto 0) & lower_reg(31 downto 4);
-- count := "100";
-- bb_reg <= "0000" & bb_reg(31 downto 4);
else
upper_reg <= sign2_reg & upper_reg(31 downto 1);
lower_reg <= upper_reg(0) & lower_reg(31 downto 1);
bb_reg <= '0' & bb_reg(31 downto 1);
end if;
else
-- Division
if sum(32) = '0' and aa_reg /= ZERO and
bb_reg(31 downto 1) = ZERO(31 downto 1) then
upper_reg <= sum(31 downto 0);
lower_reg(0) <= '1';
else
lower_reg(0) <= '0';
end if;
aa_reg <= bb_reg(1) & aa_reg(31 downto 1);
lower_reg(31 downto 1) <= lower_reg(30 downto 0);
bb_reg <= '0' & bb_reg(31 downto 1);
end if;
count_reg <= count_reg - count;
end if; --count
end case;
end if;
end process;
end; --architecture logic
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