# How to use ufixed when it involves multiplication a number of times?(VHDL question)

#### Anwesa Roy

We have to implement the following LMS equations in vhdl in a loop. y=x1w1+x2w2; w1=u*x1*e+w1; w2=u*x2*e+w2; e=y-x; However u is a floating point number and have to make the code synthesizable. Hence we have to use fixed point implementation and have to use ufixed. However when we are multiplying the numbers ,the range of the number to hold the multiplied number increases with each iteration, that is the range of the number that holds multiplication value has to be increased with each iteration. For example for eq 2:

u is ufixed(3 downto -5) x1 is ufixed(6 downto -5) e is ufixed(15 downto -10) w1 is ufixed(6 downto -5)

which makes w1 (26 downto -20) which contradicts the previous range of w1.How to resolve this issue?

Code:
``````library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
--use IEEE.STD_LOGIC_Arith.ALL;
use IEEE.STD_LOGIC_Unsigned.ALL;

use IEEE.NUMERIC_STD.ALL;
library ieee_proposed;
use ieee_proposed.fixed_pkg.all;

Library UNISIM;
use UNISIM.vcomponents.all;

entity freq_div is

generic ( width : integer :=  4 );
Port (clk_p, clk_n : in  STD_LOGIC;

LED : out  STD_LOGIC:='0';

seconds : out std_logic_vector(5 downto 0);
minutes : out std_logic_vector(5 downto 0);
hours : out std_logic_vector(4 downto 0);

random_num : out std_logic_vector (width-1 downto 0);
data_outa,data_outb,data_outc,data_outd,output : out STD_LOGIC_VECTOR(7 downto 0);

count : out  STD_LOGIC_vector(3 downto 0));
end freq_div;

architecture Behavioral of freq_div is

signal sec,min,hour : integer range 0 to 60 :=0;
signal counta : integer :=1;
signal clka : std_logic :='0';

signal clk2: std_logic;
signal cnt : std_logic_vector(3 downto 0):=(others=>'0');
signal clk: std_logic_vector(28 downto 0):=(others=>'0');

signal data_out1,rand_temp1,noisy_signal,data_outb1,data_outc1,data_outd1, summation_signal : integer;
signal noisy_signal1,s1,s2,s3,s4,s : STD_LOGIC_VECTOR(7 downto 0);
signal summation_signal1 : STD_LOGIC_VECTOR(11 downto 0);
signal i : integer :=1;
signal j : integer :=120;
signal k : integer :=40;
signal l : integer :=80;
signal ii,iii: integer :=0 ;
signal jj: integer :=30 ;
signal kk: integer :=60 ;
signal ll: integer :=90 ;
signal ii_gate: std_logic := '0';
signal a : integer := 0;

--signal n1,n2 : ufixed(127 downto -128);
--signal n3 : ufixed(255 downto -256);

signal n1,n2 : ufixed(6 downto -5);
--signal n3 : ufixed(13 downto -10);
signal n3 : ufixed(25 downto -10);

signal LED1 :STD_LOGIC := '0';

type memory_type is array (0 to 359) of std_logic_vector(7 downto 0);
signal sine2,sineo : memory_type;
--ROM for storing the sine values generated by MATLAB.
signal sine : memory_type :=(x"00",x"00",x"00",x"00",x"00",x"00",x"00",x"00",x"01",x"01",
x"01",x"01",x"01",x"01",x"02",x"02",x"02",x"02",x"03",x"03",
x"03",x"04",x"04",x"04",x"04",x"05",x"05",x"05",x"05",x"06",
x"06",x"07",x"07",x"08",x"08",x"09",x"09",x"0a",x"0a",x"0b",
x"0b",x"0c",x"0c",x"0d",x"0d",x"0e",x"0e",x"0f",x"0f",x"10",
x"11",x"11",x"12",x"13",x"13",x"14",x"15",x"15",x"16",x"17",
x"18",x"18",x"19",x"1a",x"1b",x"1b",x"1c",x"1d",x"1e",x"1e",
x"1f",x"20",x"21",x"22",x"23",x"23",x"24",x"25",x"26",x"27",
x"28",x"29",x"2a",x"2b",x"2c",x"2d",x"2f",x"2f",x"30",x"31",
x"32",x"34",x"35",x"35",x"36",x"37",x"38",x"39",x"3a",x"3b",
x"3c",x"3c",x"3e",x"3f",x"40",x"41",x"42",x"43",x"44",x"45",
x"46",x"46",x"47",x"48",x"49",x"49",x"4a",x"4b",x"4c",x"4c",
x"4e",x"4f",x"4f",x"50",x"51",x"51",x"52",x"53",x"53",x"54",
x"55",x"55",x"56",x"57",x"57",x"58",x"58",x"59",x"59",x"5a",
x"5a",x"5b",x"5b",x"5c",x"5c",x"5d",x"5d",x"5e",x"5e",x"5f",
x"5f",x"5f",x"60",x"60",x"60",x"61",x"61",x"61",x"61",x"62",
x"62",x"62",x"62",x"63",x"63",x"63",x"63",x"63",x"63",x"64",
x"64",x"64",x"64",x"64",x"64",x"64",x"64",x"64",x"64",x"64",
x"64",x"64",x"64",x"64",x"64",x"64",x"63",x"63",x"63",x"63",
x"63",x"63",x"62",x"62",x"62",x"62",x"61",x"61",x"61",x"60",
x"60",x"60",x"5f",x"5f",x"5f",x"5e",x"5e",x"5d",x"5d",x"5c",
x"5c",x"5b",x"5b",x"5a",x"5a",x"59",x"59",x"58",x"58",x"57",
x"57",x"56",x"55",x"55",x"54",x"54",x"53",x"53",x"52",x"51",
x"51",x"50",x"4f",x"4f",x"4e",x"4d",x"4c",x"4c",x"4b",x"4a",
x"49",x"49",x"48",x"47",x"46",x"46",x"45",x"44",x"44",x"43",
x"42",x"41",x"41",x"40",x"3f",x"3e",x"3d",x"3c",x"3c",x"3b",
x"3a",x"39",x"38",x"37",x"36",x"35",x"35",x"34",x"33",x"32",
x"31",x"30",x"2f",x"2f",x"2e",x"2d",x"2c",x"2b",x"2a",x"29",
x"28",x"28",x"27",x"26",x"25",x"24",x"23",x"23",x"22",x"21",
x"20",x"1f",x"1e",x"1e",x"1d",x"1c",x"1b",x"1b",x"1a",x"19",
x"18",x"18",x"17",x"16",x"15",x"15",x"14",x"13",x"13",x"12",
x"11",x"11",x"10",x"0f",x"0f",x"0e",x"0d",x"0d",x"0c",x"0c",
x"0b",x"0b",x"0a",x"0a",x"09",x"09",x"08",x"08",x"07",x"07",
x"06",x"06",x"05",x"05",x"05",x"04",x"04",x"04",x"03",x"03",
x"03",x"02",x"02",x"02",x"02",x"01",x"01",x"01",x"01",x"01",
x"01",x"00",x"00",x"00",x"00",x"00",x"00",x"00",x"00",x"00");

COMPONENT ila_1

PORT (  clk : IN STD_LOGIC;
probe0 : IN STD_LOGIC_VECTOR(3 DOWNTO 0));
END COMPONENT  ;

begin

--seconds <= conv_std_logic_vector(sec,6);
--minutes <= conv_std_logic_vector(min,6);
--hours <= conv_std_logic_vector(hour,5);

seconds <= std_logic_vector(to_signed(sec,6));
minutes <= std_logic_vector(to_signed(min,6));
hours <= std_logic_vector(to_signed(hour,5));

IBUFDS_inst : IBUFDS
generic map (
DIFF_TERM => FALSE, -- Differential Termination
IBUF_LOW_PWR => TRUE, -- Low power (TRUE) vs. performance (FALSE) setting for referenced I/O standards
IOSTANDARD => "DEFAULT")
port map (
O => clk2,  -- Buffer output
I => clk_p,  -- Diff_p buffer input (connect directly to top-level port)
IB => clk_n -- Diff_n buffer input (connect directly to top-level port)
);

process(clk2)
begin
if(clk2'event and clk2='1') then
counta <=counta+1;
if(counta = 5) then
clka <= not clka;
counta <=1;
end if;
end if;
end process;

process(clka)   --period of clk is 1 second.
variable rand_temp : std_logic_vector(width-1 downto 0):=(width-1 => '1',others => '0');
variable temp : std_logic := '0';

variable w1,w2 : ufixed(6 downto -5);
--variable w1,w2 : ufixed(42 downto -5);
variable x1,x2 : ufixed(6 downto -5);
variable u : ufixed(3 downto -5);
variable x : ufixed(14 downto -10);
variable y : ufixed(14 downto -10);
variable e : ufixed(15 downto -10);

begin
w1 :=  to_ufixed (0.0,w1);
w2 :=  to_ufixed (0.0,w2);
u :=  to_ufixed (0.05,u);

if(clka'event and clka='1') then

n1 <=  to_ufixed (51.9999,n1);         -- n1 = "00101110" = 5.75
n2 <=  to_ufixed (6.5,n2);          -- n2 = "00110100" = 6.5
n3 <= 0.2*n2*n1;

LED1 <= not LED1;
LED <= LED1;
temp := rand_temp(width-1) xor rand_temp(width-2);
rand_temp(width-1 downto 1) := rand_temp(width-2 downto 0);
rand_temp(0) := temp;

i <= i+ 1;
if(i = 359) then
i <= 0;
end if;

j <= j+ 1;
if(j = 359) then
j <= 0;
end if;

k <= k+ 1;
if(k = 359) then
k <= 0;
end if;

l <= l+ 1;
if(l = 359) then
l <= 0;
end if;

data_outa <= sine(i);

data_outb <= sine(j);
data_outc <= sine(k);
data_outd <= sine(l);

data_out1<=to_integer(unsigned(sine(i)));
random_num <= rand_temp;
rand_temp1<=to_integer(unsigned(rand_temp));
noisy_signal<=data_out1+rand_temp1;
noisy_signal1<= std_logic_vector(to_signed(noisy_signal,8));

sine2(ii)<=noisy_signal1;
sineo(ii)<=sine(i);
ii <= ii+ 1;
if(ii = 359) then
ii <=0;
ii_gate <= '1';
end if;

if ii_gate = '1' then
s1 <= sine2(iii);
s<= sineo(iii);
output <=s1;
iii <= iii+ 1;
if(iii = 359) then
iii <= 0;
end if;

x1 :=  to_ufixed (to_integer(signed(s1)),x1);
x :=  to_ufixed (to_integer(signed(s)),x);

s2 <= sine2(jj);
jj <= jj+ 1;
if(jj = 359) then
jj <= 0;
end if;
x2 :=  to_ufixed (to_integer(signed(s2)),x2);

s3 <= sine2(kk);
kk <= kk+ 1;
if(kk = 359) then
kk <= 0;
end if;
s4 <= sine2(ll);
ll <= ll+ 1;
if(ll = 359) then
ll <= 0;
end if;

if(a<1000) then
y := x1*w1+x2*w2;
e := y-x;
w1 := u*x1*e+w1;
w2 :=u*x2*e+w2;
a<=a+1;  --increment the pointer 'j'.

end if;

end if;

sec <= sec+ 1;
if(sec = 59) then
sec<=0;
min <= min + 1;
if(min = 59) then
hour <= hour + 1;
min <= 0;
if(hour = 23) then
hour <= 0;
end if;
end if;
end if;
end if;

end process;

--    process(clk2, rst)
--        begin
--            if (rst = '1')then
--                clk <= (others=>'0');
--            elsif (clk2'event and clk2 = '1')then
--                clk <= clk + 1;
--            end if;
--    end process;

--  process(clk(25), rst,up,pause)
--      begin
--      if (rst = '1') then
--          cnt <= (others=>'0');
--      elsif (clk(25) = '1' and clk(25)'event) then
--          if (up = '1' and pause = '0')then
--              cnt <= cnt + '1';
--          elsif (up = '0' and pause = '0') then
--              cnt <= cnt - '1';
--          elsif( pause ='1')then
--              cnt <= cnt;
--          end if;
--      end if;
--  end process;

--  count <= cnt;

end Behavioral;``````

Please focus on this part as the equations have been iplemented here:

Code:
``````if(a<1000) then
y := x1*w1+x2*w2;
e := y-x;
w1 := u*x1*e+w1;
w2 :=u*x2*e+w2;
a<=a+1;  --increment the pointer 'j'.

end if;``````

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