用VHDL设计一个组合移位运算符

Question

这是我的问题：我需要从零开始使用组合逻辑设计一个16位左/右逻辑/算术移位组件（除了使用std_logic_vector和std_logic）。

以下是我有：

library ieee; 
use ieee.std_logic_1164.all; 

entity Shift16 is 
    port 
    (
     -- Input ports 
     I  : in std_logic_vector(15 downto 0); 
     Shift : in std_logic_vector(3 downto 0); 

     -- Sel(1) == 0 -> Logical ; Sel(0) == Left 
     Sel : in std_logic_vector(1 downto 0); 

     -- Output ports 
     O  : out std_logic_vector(15 downto 0) 
    ); 
end Shift16; 

architecture Struct of Shift16 is 
component Mux16to1 is 
    port (I : in std_logic_vector(15 downto 0); 
      S : in std_logic_vector(3 downto 0); 
      O : out std_logic); 
end component; 

component Mux2to1_16 is 
    port 
    (A, B : in std_logic_vector(15 downto 0); S : in std_logic; 
     Q : out std_logic_vector(15 downto 0)); 
end component; 

signal OLeft, ORight : std_logic_vector(15 downto 0); 

signal PadVal : std_logic; 

type gen_signal is array (15 downto 0) of std_logic_vector(15 downto 0); 

signal leftPad, rightPad : gen_signal; 

begin 

    process (I, Sel) 
    begin 
     if (Sel(0) = '0') then -- logical 
      PadVal <= '0'; 
     else 
      PadVal <= I(15); -- aritmetic 
     end if; 

     for j in 15 downto 0 loop 
      for k in j downto 0 loop 
       leftPad(j, k) <= I(15-j); 
       rightPad(j, k) <= PadVal; 
      end loop; 

      for k in 15 downto j+1 loop 
       leftPad(j, k) <= PadVal; 
       rightPad(j, k) <= I(15-j); 
      end loop; 
     end loop; 
    end process; 



    muxarr_left_shift: for index in 15 downto 0 generate 
    begin 
     mux: Mux16to1 port map (leftPad(index), Shift, OLeft(index)); 
    end generate; 

    muxarr_right_shift: for index in 15 downto 0 generate 
    begin 
     mux: Mux16to1 port map (rightPad(index), Shift, ORight(index)); 
    end generate; 

    OutputMux: Mux2to1_16 port map (ORight, OLeft, Sel(1), O); 

end Struct; 

的Mux成分是什么，他们看起来像，只是我的定制版本。

我最初的想法是使用16个16比1的Muxs并将它​​们连接起来，这样移位量就是每个Mone的选择。这会非常快，但由于某些原因代码不能编译。

我想我也过于复杂这一点，我不知道我能做些什么做的更好..

的编译错误是：Error (10382): VHDL error at Shl16.vhd(52): index of object of array type gen_signal must have 1 dimensions

Answer 1

我想你应该改变：

for j in 15 downto 0 loop 
     for k in j downto 0 loop 
      leftPad(j, k) <= I(15-j); 
      rightPad(j, k) <= PadVal; 
     end loop; 

     for k in 15 downto j+1 loop 
      leftPad(j, k) <= PadVal; 
      rightPad(j, k) <= I(15-j); 
     end loop; 
    end loop; 

到

for j in 15 downto 0 loop 
     for k in j downto 0 loop 
      leftPad(j)(k) <= I(15-j); 
      rightPad(j)(k) <= PadVal; 
     end loop; 

     for k in 15 downto j+1 loop 
      leftPad(j)(k) <= PadVal; 
      rightPad(j)(k) <= I(15-j); 
     end loop; 
    end loop; 

因为你的类型声明。

type gen_signal is array (15 downto 0) of std_logic_vector(15 downto 0); 

P/S：如果你想保持环分配，请更改类型：

type gen_signal is array (15 downto 0, 15 downto 0) of std_logic; 

但我不认为这是适合你的端口映射。所以，你应该使用上面的方法。我使用Questasim 10.0b检查了第一种方法。

P/S（再次）：我仔细看了你的代码，发现：

process (I, Sel) 

敏感所列内容可能不适合循环，除非你想latch。我认为你应该分成2个进程。

Answer 2

如何像：

process (all) is 
    variable shift_bits : integer; 
begin 
    shift_bits := to_integer(unsigned(shift)); 
    O <= (others => '0');   -- fill with padding first - stop latch 
    if sel(0) = '1' then     -- left shift 
     O(O'high downto - O'high-shift_bits) <= 
      I(shift_bits-1 downto 0); 
    else         -- right shift 
     if sel(1) = '1' then    -- if arithmetic 
      O <= (others => I(I'high)); -- pad with sign bit 
     end if; 
     O(shift_bits-1 downto 0) <= 
      I(I'high downto i'high-shift_bits); 
    end if; 
end process; 

Synthesises 67 LUT6s

---

另一个意见 - 为什么没有明确定义的控制位，这样你就不必把意见中描述发生了什么事：

entity Shift16 is 
    port 
    (
     I    : in std_logic_vector(15 downto 0); 
     Shift_count : in unsigned(3 downto 0); 
     shift_logical : in std_logic; 
     shift_right : in std_logic; 

     O  : out std_logic_vector(15 downto 0) 
    ); 
end Shift16;