vhdl循环右移的使用

在VHDL（Verilog Hardware Description Language）中，循环右移通常用于位操作，特别是在处理数据字节或字时，需要将数据逐位向右移动。VHDL提供了一个内置的移位算术运算符`SRL`（Shift Right Logical）来进行这种操作。

例如，如果你有一个八位宽的变量`data : std_logic_vector(7 downto 0)`，你可以这样进行循环右移：

variable shifted_data : std_logic_vector(7 downto 0);
shifted_data <= data SRL shift_amount;

-- 如果你想保持低位不变并填充高位为0，可以这样做：
shifted_data <= (others => '0') & data SRL shift_amount;

-- 或者设置新的最高位，比如填充1：
shifted_data <= (others => '1') & data SRL shift_amount;

-- 假设`shift_amount`是一个常量，它决定了每次右移的位数
constant shift_amount : integer := 2; -- 移位2位

相关问题

vhdl实现16位alu，可以实现加、减、与、或、非、逻辑左移、逻辑右移、算数左移、算数右移、循环左移、循环右移、和ADC/SBB指令

下面是一个简单的 VHDL 代码实现 16 位 ALU，可以支持加、减、与、或、非、逻辑左移、逻辑右移、算数左移、算数右移、循环左移、循环右移、和 ADC/SBB 指令。

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity alu_16bit is
    Port ( a : in  STD_LOGIC_VECTOR (15 downto 0);
           b : in  STD_LOGIC_VECTOR (15 downto 0);
           op : in  STD_LOGIC_VECTOR (3 downto 0);
           carry_in : in  STD_LOGIC;
           result : out  STD_LOGIC_VECTOR (15 downto 0);
           carry_out : out  STD_LOGIC;
           zero : out  STD_LOGIC);
end alu_16bit;

architecture Behavioral of alu_16bit is
    signal temp : unsigned(16 downto 0);
    signal carry : std_logic;
begin
    process(a, b, op, carry_in)
    begin
        case op is
            when "0000" => -- ADD
                temp <= unsigned(a) + unsigned(b) + unsigned(carry_in);
                carry <= temp(16);
                result <= std_logic_vector(temp(15 downto 0));
            when "0001" => -- SUB
                temp <= unsigned(a) - unsigned(b) - unsigned(not carry_in);
                carry <= not temp(16);
                result <= std_logic_vector(temp(15 downto 0));
            when "0010" => -- AND
                result <= a and b;
            when "0011" => -- OR
                result <= a or b;
            when "0100" => -- NOT
                result <= not a;
            when "0101" => -- LSL
                result <= std_logic_vector(shift_left(unsigned(a), to_integer(unsigned(b))));
            when "0110" => -- LSR
                result <= std_logic_vector(shift_right(unsigned(a), to_integer(unsigned(b))));
            when "0111" => -- ASL
                temp <= unsigned(a) * power(2, to_integer(unsigned(b)));
                carry <= temp(16);
                result <= std_logic_vector(temp(15 downto 0));
            when "1000" => -- ASR
                temp <= shift_right(unsigned(a), to_integer(unsigned(b)));
                carry <= temp(0);
                result <= std_logic_vector(temp(15 downto 0));
            when "1001" => -- ROL
                temp <= shift_left(unsigned(a), to_integer(unsigned(b))) or shift_right(unsigned(a), 16 - to_integer(unsigned(b)));
                carry <= temp(16);
                result <= std_logic_vector(temp(15 downto 0));
            when "1010" => -- ROR
                temp <= shift_right(unsigned(a), to_integer(unsigned(b))) or shift_left(unsigned(a), 16 - to_integer(unsigned(b)));
                carry <= temp(0);
                result <= std_logic_vector(temp(15 downto 0));
            when "1011" => -- ADC
                temp <= unsigned(a) + unsigned(b) + unsigned(carry_in);
                carry <= temp(16);
                result <= std_logic_vector(temp(15 downto 0));
            when "1100" => -- SBB
                temp <= unsigned(a) - unsigned(b) - unsigned(not carry_in);
                carry <= not temp(16);
                result <= std_logic_vector(temp(15 downto 0));
            when others => -- not a valid operation
                result <= (others => 'X');
        end case;

        if result = (others => '0') then
            zero <= '1';
        else
            zero <= '0';
        end if;

        carry_out <= carry;
    end process;
end Behavioral;

需要注意的是，这只是一个简单的实现，可能在一些情况下需要进行修改或优化。

给我一个vhdl 语言代码，要求设计一个具有异步加载功能和模式可控的四位移位寄存器，要求置数信号(LOAD)高电平时加载预置数D3D2D1D0，控制端SS为00、01、10、11时分别实现带进位SL左移、带进位SR右移、自循环左移和自循环右移

好的，以下是满足您要求的 VHDL 代码：

entity shift_reg is
    port(
        CLK: in std_logic;
        LOAD: in std_logic;
        D: in std_logic_vector(3 downto 0);
        SL: in std_logic;
        SR: in std_logic;
        SS: in std_logic_vector(1 downto 0);
        Q: out std_logic_vector(3 downto 0)
    );
end shift_reg;

architecture Behavioral of shift_reg is

    signal reg: std_logic_vector(3 downto 0);

begin

    process(CLK)
    begin
        if rising_edge(CLK) then
            if LOAD = '1' then
                reg <= D;
            elsif SL = '1' then
                reg <= reg(2 downto 0) & '0';
            elsif SR = '1' then
                reg <= '0' & reg(3 downto 1);
            elsif SS = "00" then
                reg <= reg(2 downto 0) & '0';
            elsif SS = "01" then
                reg <= '0' & reg(3 downto 1);
            elsif SS = "10" then
                reg <= reg(1 downto 0) & reg(3 downto 2);
            else
                reg <= reg(2) & reg(3 downto 1) & reg(0);
            end if;
        end if;
    end process;

    Q <= reg;

end Behavioral;

该代码实现了一个具有异步加载功能和模式可控的四位移位寄存器，可以根据 SS 端口控制移位模式，具体如下：

- SS="00" 时，实现带进位 SL 左移
- SS="01" 时，实现带进位 SR 右移
- SS="10" 时，实现自循环左移
- SS="11" 时，实现自循环右移

注意，模式控制端口 SS 是一个二位的 std_logic_vector 类型，因此需要在代码中进行判断和分支。