使用FPGA实现串-并型乘法器

介绍

其实我们知道，用FPGA实现乘法器并不是一件很简单的事，而且在FPGA中也有乘法器的IP核可以直接调用，我这里完全就是为了熟悉一些FPGA的语法然后写了这样一个电路。

串-并型乘法器模块

从字面上看，串-并乘法器就是其中一个乘数是串行的，另一位乘数是并行的。我在这里只描述一下模块的输入输出端口，相比于并行乘法器，串-并型乘法器占用的资源更少。

在这里，a是串行的数据，b是并行的4位数据，output也是串行的数据。

设计文件

这里我把基础的与门，D触发器和乘法器都给省略掉了。

--pipe元件

library ieee;
use ieee.std_logic_1164.all;
use work.my_component.all;
entity pipe is
   port( a,b,clk,rst : in std_logic;
           d_reg_out : out std_logic);
end entity;
architecture behavior of pipe is
   signal f_add_outc,cin,f_add_outs : std_logic;
begin
   u1 : component f_add
   port map(a,b,cin,f_add_outs,f_add_outc);
   u2 : component d_reg
   port map(f_add_outc,clk,rst,cin);
   u3 : component d_reg
   port map(f_add_outs,clk,rst,d_reg_out);
end architecture;

--packeg声明元件

library ieee;
use ieee.std_logic_1164.all;
package my_component is
------------------------------------
component and_2 is
   port( a,b : in std_logic;
           and_2_out: out std_logic);
end component;
------------------------------------
component d_reg is
   port( d_reg_in,clk,rst : in std_logic;
           d_reg_out : out std_logic);
end component;
------------------------------------
component f_add is
   port (a,b,cin : in std_logic;
           f_add_outs,f_add_outc : out std_logic);
end component;
------------------------------------
component pipe is
   port( a,b,clk,rst : in std_logic;
           d_reg_out : out std_logic);
end component;
end package;

顶层文件

library ieee;
use ieee.std_logic_1164.all;
use work.my_component.all;
entity multiplier is
   port( a,rst,clk : in std_logic;
           b : in std_logic_vector(3 downto 0);
           output : out std_logic);
end entity;
architecture behavior of multiplier is
   signal and_out,reg_out : std_logic_vector(3 downto 0);
begin
   u1: component and_2 port map(a,b(3),and_out(3));
   u2: component and_2 port map(a,b(2),and_out(2));
   u3: component and_2 port map(a,b(1),and_out(1));
   u4: component and_2 port map(a,b(0),and_out(0));
   u5: component d_reg port map(and_out(3),clk,rst,reg_out(3));
   u6: component pipe port map(and_out(2),reg_out(3),clk,rst,reg_out(2));
   u7: component pipe port map(and_out(1),reg_out(2),clk,rst,reg_out(1));
   u8: component pipe port map(and_out(0),reg_out(1),clk,rst,reg_out(0));
   output <= reg_out(0);
end behavior;

测试文件

在测试文件中，我只对顶层文件进行了测试，有兴趣的小伙伴可以对各个信号进行仿真验证。

library ieee;
use ieee.std_logic_1164.all;
use work.my_component.all;
entity tb_multiplier is

end entity;
architecture behavior of tb_multiplier is
   component multiplier is
       port( a,rst,clk : in std_logic;
               b : in std_logic_vector(3 downto 0);
               output : out std_logic);
   end component;
   signal a,rst,clk : std_logic := '0';
   signal output : std_logic := '1';
   signal b : std_logic_vector(3 downto 0);
begin
   dut : multiplier
   port map(a,rst,clk,b,output);
   process
   begin
       clk <= '1';
       wait for 10ns;
       clk <= '0';
       wait for 10ns;
   end process;
   process
   begin
       a <= '0';
       b <= "1101";
       wait for 40ns;
       a <= '1';
       wait for 40ns;
       a <= '0';
       wait for 80ns;
   end process;
end architecture;