The following information has been generated by Exemplar Logic and
-- may be freely distributed and modified.
--
-- Design name : pseudorandom
--
-- Purpose : This design is a pseudorandom number generator. This design
-- will generate an 8-bit random number using the polynomial p(x) = x + 1.
-- This system has a seed generator and will generate 2**8 - 1 unique
-- vectors in pseudorandom order. These vectors are stored in a ram which
-- samples the random number every 32 clock cycles. This variance of a
-- priority encoded seed plus a fixed sampling frequency provides a truely
-- random number.
--
-- This design used VHDL-1993 methods for coding VHDL.
--
----------------------------------------------------------------------------
Library IEEE ;
use IEEE.std_logic_1164.all ;
use IEEE.std_logic_arith.all ;
entity divide_by_n is
generic (data_width : natural := 8 );
port (
data_in : in UNSIGNED(data_width - 1 downto 0) ;
load : in std_logic ;
clk : in std_logic ;
reset : in std_logic ;
divide : out std_logic
);
end divide_by_n ;
architecture rtl of divide_by_n is
signal count_reg : UNSIGNED(data_width - 1 downto 0) ;
constant max_count : UNSIGNED(data_width - 1 downto 0) := (others => '1') ;
begin
cont_it : process(clk,reset)
begin
if (reset = '1') then
count_reg <= (others => '0') ;
elsif (clk = '1' and clk'event) then
if (load = '1') then
count_reg <= data_in ;
else
count_reg <= count_reg + "01" ;
end if ;
end if;
end process ;
divide <= '1' when count_reg = max_count else '0' ;
end RTL ;
Library IEEE ;
use IEEE.std_logic_1164.all ;
use IEEE.std_logic_arith.all ;
entity dlatrg is
generic (data_width : natural := 16 );
port (
data_in : in UNSIGNED(data_width - 1 downto 0) ;
clk : in std_logic ;
reset : in std_logic ;
data_out : out UNSIGNED(data_width - 1 downto 0)
);
end dlatrg ;
architecture rtl of dlatrg is
begin
latch_it : process(data_in,clk,reset)
begin
if (reset = '1') then
data_out <= (others => '0') ;
elsif (clk = '1') then
data_out <= data_in ;
end if;
end process ;
end RTL ;
Library IEEE ;
use IEEE.std_logic_1164.all ;
use IEEE.std_logic_arith.all ;
entity lfsr is
generic (data_width : natural := 8 );
port (
clk : in std_logic ;
reset : in std_logic ;
data_out : out UNSIGNED(data_width - 1 downto 0)
);
end lfsr ;
architecture rtl of lfsr is
signal feedback : std_logic ;
signal lfsr_reg : UNSIGNED(data_width - 1 downto 0) ;
begin
feedback <= lfsr_reg(7) xor lfsr_reg(0) ;
latch_it : process(clk,reset)
begin
if (reset = '1') then
lfsr_reg <= (others => '0') ;
elsif (clk = '1' and clk'event) then
lfsr_reg <= lfsr_reg(lfsr_reg'high - 1 downto 0) & feedback ;
end if;
end process ;
data_out <= lfsr_reg ;
end RTL ;
Library IEEE ;
use IEEE.std_logic_1164.all ;
use IEEE.std_logic_arith.all ;
entity priority_encoder is
generic (data_width : natural := 25 ;
address_width : natural := 5 ) ;
port (
data : in UNSIGNED(data_width - 1 downto 0) ;
address : out UNSIGNED(address_width - 1 downto 0) ;
none : out STD_LOGIC
);
end priority_encoder ;
architecture rtl of priority_encoder is
attribute SYNTHESIS_RETURN : STRING ;
FUNCTION to_stdlogic (arg1:BOOLEAN) RETURN STD_LOGIC IS
BEGIN
IF(arg1) THEN
RETURN('1') ;
ELSE
RETURN('0') ;
END IF ;
END ;
function to_UNSIGNED(ARG: INTEGER; SIZE: INTEGER) return UNSIGNED is
variable result: UNSIGNED(SIZE-1 downto 0);
variable temp: integer;
attribute SYNTHESIS_RETURN of result:variable is "FEED_THROUGH" ;
begin
temp := ARG;
for i in 0 to SIZE-1 loop
if (temp mod 2) = 1 then
result(i) := '1';
else
result(i) := '0';
end if;
if temp > 0 then
temp := temp / 2;
else
temp := (temp - 1) / 2;
end if;
end loop;
return result;
end;
constant zero : UNSIGNED(data_width downto 1) := (others => '0') ;
begin
PRIO : process(data)
variable temp_address : UNSIGNED(address_width - 1 downto 0) ;
begin
temp_address := (others => '0') ;
for i in data_width - 1 downto 0 loop
if (data(i) = '1') then
temp_address := to_unsigned(i,address_width) ;
exit ;
end if ;
end loop ;
address <= temp_address ;
none <= to_stdlogic(data = zero) ;
end process ;
end RTL ;
Library IEEE ;
use IEEE.std_logic_1164.all ;
use IEEE.std_logic_arith.all ;
use IEEE.std_logic_unsigned.all ;
entity ram is
generic (data_width : natural := 8 ;
address_width : natural := 8);
port (
data_in : in UNSIGNED(data_width - 1 downto 0) ;
address : in UNSIGNED(address_width - 1 downto 0) ;
we : in std_logic ;
clk : in std_logic;
data_out : out UNSIGNED(data_width - 1 downto 0)
);
end ram ;
architecture rtl of ram is
type mem_type is array (2**address_width downto 0) of UNSIGNED(data_width - 1 downto 0) ;
signal mem : mem_type ;
signal addr_reg : unsigned (address_width -1 downto 0);
begin
data_out <= mem(conv_integer(addr_reg)) ;
I0 : process
begin
wait until clk'event and clk = '1';
if (we = '1') then
mem(conv_integer(address)) <= data_in ;
end if ;
addr_reg <= address;
end process ;
end RTL ;
Library IEEE ;
use IEEE.std_logic_1164.all ;
use IEEE.std_logic_arith.all ;
entity tbuf is
generic (data_width : natural := 16 );
port (
data_in : in UNSIGNED(data_width - 1 downto 0) ;
en : in std_logic ;
data_out : out UNSIGNED(data_width - 1 downto 0)
);
end tbuf ;
architecture rtl of tbuf is
begin
three_state : process(data_in,en)
begin
if (en = '1') then
data_out <= data_in ;
else
data_out <= (others => 'Z') ;
end if;
end process ;
end RTL ;
Library IEEE ;
use IEEE.std_logic_1164.all ;
use IEEE.std_logic_arith.all ;
entity pseudorandom is
generic (data_width : natural := 8 );
port (
seed : in UNSIGNED (24 downto 0) ;
init : in UNSIGNED (4 downto 0) ;
load : in std_logic ;
clk : in std_logic ;
reset : in std_logic ;
read : in std_logic ;
write : in std_logic ;
rand : out UNSIGNED (7 downto 0) ;
none : out std_logic
);
end pseudorandom ;
architecture rtl of pseudorandom is
signal latch_seed : UNSIGNED(24 downto 0) ;
signal encoder_address : UNSIGNED(4 downto 0) ;
signal random_data : UNSIGNED(7 downto 0) ;
signal write_enable : std_logic ;
signal ram_data : UNSIGNED(7 downto 0) ;
begin
I0 : entity work.dlatrg(rtl)
generic map (25)
port map (seed,read,reset,latch_seed) ;
I1 : entity work.priority_encoder(rtl)
generic map (25,5)
port map (latch_seed,encoder_address,none) ;
I2 : entity work.ram(rtl)
generic map (8,5)
port map (random_data,encoder_address,write_enable,clk,ram_data) ;
I3 : entity work.tbuf(rtl)
generic map (8)
port map (ram_data,write,rand) ;
I4 : entity work.lfsr(rtl)
generic map (8)
port map (clk,reset,random_data) ;
I5 : entity work.divide_by_n(rtl)
generic map (5)
port map (init,load,clk,reset,write_enable) ;
end rtl ;