m_table.vhd

Intel微处理器8088的VHDL实现

-------------------------------------------------------------------------------
--  CPU86 - VHDL CPU8088 IP core                                             --
--  Copyright (C) 2005-2008 HT-LAB                                           --
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--  CPU86 is released as open-source under the Aladdin Free Public License.  --
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--  Full details of the license can be found in the file "cpu86_license.txt" --
--  which is included in the distribution zip file.                          --
-------------------------------------------------------------------------------

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;

entity m_table is
  port ( ireg  : in std_logic_vector(7 downto 0);
         modrrm: in std_logic_vector(7 downto 0);
         muxout: out std_logic_vector(7 downto 0));
end m_table;


architecture rtl of m_table is

  signal lutout_s: std_logic_vector(1 downto 0);
  signal ea_s    : std_logic;                                   -- Asserted if mod=00 and rm=110
  signal m11_s   : std_logic;                                   -- Asserted if mod=11
  signal mux_s   : std_logic_vector(3 downto 0);

begin

  ea_s <= '1' when (modrrm(7 downto 6)="00" and modrrm(2 downto 0)="110") else '0';
  m11_s<= '1' when modrrm(7 downto 6)="11" else '0';
  mux_s <= lutout_s & m11_s & ea_s;

  process (mux_s,modrrm)
  begin
    case mux_s is
       when "1000" => muxout <= modrrm(7 downto 6)&"000000";   -- only check mod value
       when "1010" => muxout <= modrrm(7 downto 6)&"000000";   -- only check mod value
       when "1001" => muxout <= "00000110";                    -- mod000rm
       when "1011" => muxout <= "00000110";                    -- mod000rm
       when "1100" => muxout <= modrrm(7 downto 3)&"000";      -- mod IST 000
       when "1101" => muxout <= "00"&modrrm(5 downto 3)&"110"; -- 00 IST 110 
       when "1110" => muxout <= "11"&modrrm(5 downto 3)&"000"; -- 11 IST 000 
       when others => muxout <= (others => '0');               -- single instruction
    end case;
  end process;

  process(ireg)
  begin
    case ireg is
       when "11111111" => lutout_s <= "11";  
       when "10001000" => lutout_s <= "10";  
       when "10001001" => lutout_s <= "10";  
       when "10001010" => lutout_s <= "10";  
       when "10001011" => lutout_s <= "10";  
       when "11000110" => lutout_s <= "11";  
       when "11000111" => lutout_s <= "11";  
       when "10001110" => lutout_s <= "10";  
       when "10001100" => lutout_s <= "10";  
       when "10001111" => lutout_s <= "11";  
       when "10000110" => lutout_s <= "10";  
       when "10000111" => lutout_s <= "10";  
       when "10001101" => lutout_s <= "10";  
       when "11000101" => lutout_s <= "10";  
       when "11000100" => lutout_s <= "10";  
       when "00000000" => lutout_s <= "10";  
       when "00000001" => lutout_s <= "10";  
       when "00000010" => lutout_s <= "10";  
       when "00000011" => lutout_s <= "10";  
       when "10000000" => lutout_s <= "11";  
       when "10000001" => lutout_s <= "11";  
       when "10000011" => lutout_s <= "11";  
       when "00010000" => lutout_s <= "10";  
       when "00010001" => lutout_s <= "10";  
       when "00010010" => lutout_s <= "10";  
       when "00010011" => lutout_s <= "10";  
       when "00101000" => lutout_s <= "10";  
       when "00101001" => lutout_s <= "10";  
       when "00101010" => lutout_s <= "10";  
       when "00101011" => lutout_s <= "10";  
       when "00011000" => lutout_s <= "10";  
       when "00011001" => lutout_s <= "10";  
       when "00011010" => lutout_s <= "10";  
       when "00011011" => lutout_s <= "10";  
       when "11111110" => lutout_s <= "11";  
       when "00111010" => lutout_s <= "10";  
       when "00111011" => lutout_s <= "10";  
       when "00111000" => lutout_s <= "10";  
       when "00111001" => lutout_s <= "10";  
       when "11110110" => lutout_s <= "11";  
       when "11110111" => lutout_s <= "11";  
       when "11010000" => lutout_s <= "10";  
       when "11010001" => lutout_s <= "10";  
       when "11010010" => lutout_s <= "10";  
       when "11010011" => lutout_s <= "10";  
       when "00100000" => lutout_s <= "10";  
       when "00100001" => lutout_s <= "10";  
       when "00100010" => lutout_s <= "10";  
       when "00100011" => lutout_s <= "10";  
       when "00001000" => lutout_s <= "10";  
       when "00001001" => lutout_s <= "10";  
       when "00001010" => lutout_s <= "10";  
       when "00001011" => lutout_s <= "10";  
       when "10000100" => lutout_s <= "10";  
       when "10000101" => lutout_s <= "10";  
       when "00110000" => lutout_s <= "10"; 
       when "00110001" => lutout_s <= "10"; 
       when "00110010" => lutout_s <= "10"; 
       when "00110011" => lutout_s <= "10"; 
       when others     => lutout_s <= "00"; 
    end case;
  end process;
end rtl;