在 VHDL 中使用 LFSR 的伪随机数生成器

Question

我在使用 lfsr 方法创建 prng 时遇到了一些麻烦。这是我的代码：

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity pseudorng is
Port ( clock : in STD_LOGIC;
       reset : in STD_LOGIC;
       Q : out STD_LOGIC_VECTOR (7 downto 0);
       check: out STD_LOGIC);

       constant seed: STD_LOGIC_VECTOR(7 downto 0) := "00000001";
end pseudorng;

architecture Behavioral of pseudorng is

signal temp: STD_LOGIC;
signal Qt: STD_LOGIC_VECTOR(7 downto 0);

begin

PROCESS(clock)
BEGIN

IF rising_edge(clock) THEN
IF (reset='1') THEN Qt <= "00000000";
ELSE Qt <= seed; 
END IF;
temp <= Qt(4) XOR Qt(3) XOR Qt(2) XOR Qt(0);
--Qt <= temp & Qt(7 downto 1);

END IF;
END PROCESS;

check <= temp;
Q <= Qt;

end Behavioral;

这是我的模拟运行： prng sim

首先，检查输出就在那里，所以我可以监控温度信号的输出。其次，被注释掉的行是导致问题的原因。

从仿真中可以看出，在时钟的第一个上升沿，Qt信号读取种子。然而，这是我的问题，出于某种原因，temp 信号仅在时钟的第二个上升沿对 Qt 信号的位进行异或运算。它在第一个时钟脉冲上保持未定义状态。这是为什么？如果它在 Qt 信号读取种子后立即在第一个上升沿运行，那么我可以取消注释移动位的行，这将解决我的问题。任何帮助将不胜感激！

如果有人关心，这里是测试台：

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity tb_pseudorng is
end tb_pseudorng;

architecture bench of tb_pseudorng is

COMPONENT pseudorng
      Port ( clock : in STD_LOGIC;
      reset : in STD_LOGIC;
      Q : out STD_LOGIC_VECTOR (7 downto 0);
      check: out STD_LOGIC);
END COMPONENT;

signal clock1: STD_LOGIC;
signal reset1: STD_LOGIC;
signal Q1: STD_LOGIC_VECTOR(7 downto 0);
signal check1: STD_LOGIC;

begin

mapping: pseudorng PORT MAP(
clock => clock1,
reset => reset1,
Q => Q1,
check => check1);

clock: PROCESS
BEGIN
clock1<='0'; wait for 50ns;
clock1<='1'; wait for 50ns;
END PROCESS;

reset: PROCESS
BEGIN
reset1<='0'; wait for 900ns;
END PROCESS; 

end bench;

Answer 1

我对你的内容做了一些细微的修改（虽然你已经差不多了）；我不认为 LFSR 会采取其他措施。我向 LFSR 添加了一个使能信号，这样您就可以有效地控制它何时启动。结果模拟是 here.

作为旁注，如果您想为 LFSR 设置不同的值（而不是使其成为常量），您还可以包含 load 和 seed 输入。

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity pseudorng is
Port ( clock : in STD_LOGIC;
       reset : in STD_LOGIC;
       en : in STD_LOGIC;
       Q : out STD_LOGIC_VECTOR (7 downto 0);
       check: out STD_LOGIC);

--       constant seed: STD_LOGIC_VECTOR(7 downto 0) := "00000001";
end pseudorng;

architecture Behavioral of pseudorng is

--signal temp: STD_LOGIC;
signal Qt: STD_LOGIC_VECTOR(7 downto 0) := x"01";

begin

PROCESS(clock)
variable tmp : STD_LOGIC := '0';
BEGIN

IF rising_edge(clock) THEN
   IF (reset='1') THEN
   -- credit to QuantumRipple for pointing out that this should not
   -- be reset to all 0's, as you will enter an invalid state
      Qt <= x"01"; 
   --ELSE Qt <= seed;
   ELSIF en = '1' THEN
      tmp := Qt(4) XOR Qt(3) XOR Qt(2) XOR Qt(0);
      Qt <= tmp & Qt(7 downto 1);
   END IF;

END IF;
END PROCESS;
-- check <= temp;
check <= Qt(7);
Q <= Qt;

end Behavioral;

待定：

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity tb_pseudorng is
end tb_pseudorng;

architecture bench of tb_pseudorng is

COMPONENT pseudorng
      Port ( clock : in STD_LOGIC;
      reset : in STD_LOGIC;
      en : in STD_LOGIC;
      Q : out STD_LOGIC_VECTOR (7 downto 0);
      check: out STD_LOGIC);
END COMPONENT;

signal clock1: STD_LOGIC;
signal reset1: STD_LOGIC;
signal Q1: STD_LOGIC_VECTOR(7 downto 0);
signal check1: STD_LOGIC;
signal en : STD_LOGIC;

begin

mapping: pseudorng PORT MAP(
clock => clock1,
reset => reset1,
en => en,
Q => Q1,
check => check1);

clock: PROCESS
BEGIN
   clock1 <= '0'; wait for 50 ns;
   clock1 <= '1'; wait for 50 ns;
END PROCESS;

reset: PROCESS
BEGIN
   reset1 <= '0';
   en <= '1';
   wait for 900 ns;
END PROCESS;

end bench;

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