alu.vhd

实现了CPU的基本功能

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity ALU is
port(reset,clk:in std_logic;
     BR_DATA,ACC_DATA:in std_logic_vector(15 downto 0);
     CBR_DATA:in std_logic_vector(11 downto 0);
     ACC,MR,DR:out std_logic_vector(15 downto 0);
     FLAGS:out std_logic_vector(1 downto 0)
);
end entity;
architecture ALU_arc of ALU is
begin
process(reset,clk,CBR_DATA)
variable temp_acc:std_logic_vector(15 downto 0);
variable temp_mr:std_logic_vector(16 downto 0);
variable counter:integer;
variable sign:std_logic;
variable temp,temp_dr:std_logic_vector(15 downto 0);
begin
if reset='1' then
    temp_acc:="0000000000000000";
    FLAGS<="00";
  elsif clk'event and clk='1' then
        case CBR_DATA is 
            when "000000000001"=>temp_acc:="0000000000000000";
            when "000000000010"=>temp_acc:=ACC_DATA+BR_DATA;
            when "000000000100"=>temp_acc:=ACC_DATA-BR_DATA;
            when "000000001000"=>temp_acc:=ACC_DATA and BR_DATA;
            when "000000010000"=>temp_acc:=ACC_DATA or BR_DATA;
            when "000000100000"=>temp_acc:=not ACC_DATA;
            when "000001000000"=>temp_acc:='0'&ACC_DATA(15 downto 1);
            when "000010000000"=>temp_acc:=ACC_DATA(14 downto 0)&'0';
            when "000100000000"=>
                 counter:=16;
                 temp_mr:=ACC_DATA&'0';
                 temp_acc:="0000000000000000";
            when "001000000000"=>  
                if temp_mr(1)='1' and temp_mr(0)='0' then
                       temp_acc:=temp_acc-BR_DATA;
                     elsif temp_mr(1)='0' and temp_mr(0)='1' then
                          temp_acc:=temp_acc+BR_DATA;
                end if;
                 counter:=counter-1;
                 temp_mr:=temp_acc(0)&temp_mr(16 downto 1);
                 if temp_acc(15)='1' then 
                       temp_acc:='1'&temp_acc(15 downto 1);
                    else
                        temp_acc:='0'&temp_acc(15 downto 1);
                 end if;
            when "010000000000"=>
                  counter:=16;
                  temp_dr:=ACC_DATA;
                  if ACC_DATA(15)='1' then
                        temp_acc:="1111111111111111";
                     else
                        temp_acc:="0000000000000000";
                  end if;
                  if ACC_DATA(15)=BR_DATA(15) then
                         sign:='0';
                      else
                         sign:='1';
                  end if;
            when "100000000000"=>
                  counter:=counter-1;
                  temp_acc:=temp_acc(14 downto 0)&temp_dr(15);
                  temp_dr:=temp_dr(14 downto 0)&'0';
                  temp:=temp_acc;
                  if BR_DATA(15)=temp(15) then
                         temp:=temp-BR_DATA;
                      else
                         temp:=temp+BR_DATA;
                  end if;
                  if temp(15)=temp_acc(15) or (temp="0000000000000000" and temp_dr="0000000000000000") then
                         temp_acc:=temp;
                         temp_dr(0):='1';
                     else
                         temp_dr(0):='0';
                  end if;
                  if counter=0 then
                        if sign='1' then
                              temp_dr:=not temp_dr;
                              temp_dr:=temp_dr+1;
                        end if;
                  end if;
            when others=>null;
        end case;
        if counter=0 then
                FLAGS(1)<='1';
            else
                 FLAGS(1)<='0';
        end if;
        if temp_acc(15)='0' then
               FLAGS(0)<='1';
           else
               FLAGS(0)<='0';
        end if;
end if;
ACC<=temp_acc;
MR<=temp_mr(16 downto 1);
DR<=temp_dr;
end process;
end ALU_arc;