armshiefter.vhd

用VHDL语言实现的ARM处理器的标准内核的源代码程序

          --  64  63               33  32 31          1  0
          -- +---+---+---------------+===+=============+---+
          -- |           000         | c |    op1-1        |
          -- +---+---+---------------+===+=============+ccc+
          --                                                 : rrx 
          
          shiftin(31 downto 0) := data2;
          shiftin(32) := carry;
          op2 := (others => '0');
          
          carryoutsrc := shiftin_00;
          
        when ash_sdir_snone =>
          op2 := (others => '0');
        when others => null;
      end case;


      
    when ash_styp_sreg =>

      shiftin := (others => '0');
      shiftin(32 downto 1) := data1;

      case dir  is 
        when ash_sdir_slsl =>
      
          --$(del)
          --if Rs[7:0] == 0 then
          --  shifter_operand = Rm
          --  shifter_carry_out = C Flag
          --else if Rs[7:0] < 32 then
          --  shifter_operand = Rm Logical_Shift_Left Rs[7:0]
          --  shifter_carry_out = Rm[32 - Rs[7:0]]
          --else if Rs[7:0] == 32 then
          --  shifter_operand = 0
          --  shifter_carry_out = Rm[0]
          --else /* Rs[7:0] > 32 */
          --  shifter_operand = 0
          --  shifter_carry_out = 0
          --$(/del)

          --  64  63               33  32 31          1  0
          -- +---+---+---------------+===+=============+---+
          -- | c |           op1         |    000      | 0 |
          -- +---+---+------------ccc+===+=============+---+
          --       c |    op1            |                   << 31 (>>0)
          --                       c |       op1       |     << 0 (>>31)
            
          shiftin := (others => '0');
          shiftin(64) := carry;
          shiftin(63 downto 32) := data1;
          op2 := not data2(4 downto 0);
          
          carryoutsrc := shiftin_33;
          
          if not (data2(7 downto 5) = "000") then -- >= 32
            shiftin := (others => '0');
            if data2(7 downto 0) = "00100000" then  -- == 32
              carryoutsrc := shiftin_prev;
              carryout := data1(0);
            end if;
          end if;
          
        when ash_sdir_slsr =>

          --$(del)
          --if Rs[7:0] == 0 then
          --  shifter_operand = Rm
          --  shifter_carry_out = C Flag
          --else if Rs[7:0] < 32 then
          --  shifter_operand = Rm Logical_Shift_Right Rs[7:0]
          --  shifter_carry_out = Rm[Rs[7:0] - 1]
          --else if Rs[7:0] == 32 then
          --  shifter_operand = 0
          --  shifter_carry_out = Rm[31]
          --else /* Rs[7:0] > 32 */
          --  shifter_operand = 0
          --  shifter_carry_out = 0
          --$(/del)
      
          --  64  63               33  32 31          1  0
          -- +---+---+---------------+===+=============+---+
          -- | 0 | 0 |    000        |        op1      | c |
          -- +---+---+---------------+===+=============+ccc+
          --                         |     op1         |     >> 0
          --                                       |op1|     >> 31 
          
          shiftin := (others => '0');
          shiftin(0) := carry;
          shiftin(32 downto 1) := data1;
          op2 := data2(4 downto 0);

          carryoutsrc := shiftin_00;
          
          if not (data2(7 downto 5) = "000") then -- >= 32
            shiftin := (others => '0');
            if data2(7 downto 0) = "00100000" then  -- == 32
              carryoutsrc := shiftin_prev;
              carryout := data1(31);
            end if;
          end if;
          
        when ash_sdir_sasr =>
          --$(del)
          --if Rs[7:0] == 0 then
          --  shifter_operand = Rm
          --  shifter_carry_out = C Flag
          --else if Rs[7:0] < 32 then
          --  shifter_operand = Rm Arithmetic_Shift_Right Rs[7:0]
          --  shifter_carry_out = Rm[Rs[7:0] - 1]
          --else /* Rs[7:0] >= 32 */
          --  if Rm[31] == 0 then
          --    shifter_operand = 0
          --    shifter_carry_out = Rm[31]
          --  else /* Rm[31] == 1 */
          --    shifter_operand = 0xFFFFFFFF
          --    shifter_carry_out = Rm[31]
          --$(/del)

          --  64  63               33  32 31          1  0
          -- +---+---+---------------+===+=============+---+
          -- | s | s |    sss        |        op1      | c |
          -- +---+---+---------------+===+=============+ccc+
          --                           s |    op1      |     >> 1
          --                                  sss  |op1|     >> 31 
          --                                  000      | 0   >> 0 (s=0)
          --                                  111      | 1   >> 0 (s=1)
          if data1(31) = '1' then
            shiftin(64 downto 33) := (others => '1');
          else
            shiftin(64 downto 33) := (others => '0');
          end if;
          shiftin(0) := carry;
          shiftin(32 downto 1) := data1;
          op2 := data2(4 downto 0);
          
          if not (data2(7 downto 5) = "000") then -- >= 32
            if data1(31) = '1' then
              shiftin(32 downto 0) := (others => '1');
            else
              shiftin(32 downto 0) := (others => '0');
            end if;
          end if;
          
          carryoutsrc := shiftin_00;
      
        when ash_sdir_sror =>
      
          --$(del)
          --if Rs[7:0] == 0 then
          --  shifter_operand = Rm
          --  shifter_carry_out = C Flag
          --else if Rs[4:0] == 0 then
          --  shifter_operand = Rm 
          --  shifter_carry_out = Rm[31]
          --else /* Rs[4:0] > 0 */
          --  shifter_operand = Rm Rotate_Right Rs[4:0]
          --  shifter_carry_out = Rm[Rs[4:0] - 1]
          --$(/del)

          --  64  63               33  32 31          1  0
          -- +---+---+---------------+===+=============+---+
          -- |           op1         |       op1       | 0 |
          -- +---+---+---------------+ccc+=============+---+
          --         |    op1            |                   <<  1 (>>1) 
          --                      |       op1       |        << 31 (>>31)

          shiftin := (others => '0');
          shiftin(64 downto 33) := data1;
          shiftin(32 downto 1) := data1;
          op2 := data2(4 downto 0);
          
          carryoutsrc := shiftin_32;
          
          if data2(7 downto 0) = "00000000" then -- == 0
            carryoutsrc := shiftin_prev;
            carryout := carry;
          end if;
          
        when ash_sdir_srrx =>
      
          --$(del)
          --shifter_operand = (C Flag Logical_Shift_Left 31) OR (Rm Logical_Shift_Right 1)
          --shifter_carry_out = Rm[0]
          --$(/del)
          
          --  64  63               33  32 31          1  0
          -- +---+---+---------------+===+=============+---+
          -- |           000         | c |    op1-1        |
          -- +---+---+---------------+===+=============+ccc+
          --                                                 : rrx
          
          op2 := (others => '0');
          shiftin(31 downto 0) := carry & shiftin(31 downto 1);
          
        when ash_sdir_snone =>
        when others => null;
      end case;
      
    when ash_styp_none =>
      
      shiftin := (others => '0');
      shiftin(32 downto 1) := data2;
      
    when others => 
  end case;
  
  -- shifter
  if op2 (4) = '1' then
    shiftin(48 downto 0) := shiftin(64 downto 16);
  end if;
  if op2 (3) = '1' then
    shiftin(40 downto 0) := shiftin(48 downto 8);
  end if;
  if op2 (2) = '1' then
    shiftin(36 downto 0) := shiftin(40 downto 4);
  end if;
  if op2 (1) = '1' then
    shiftin(34 downto 0) := shiftin(36 downto 2);
  end if;
  if op2 (0) = '1' then
    shiftin(32 downto 0) := shiftin(33 downto 1);
  end if;

  -- carry out select
  case carryoutsrc is
    when shiftin_00   => carryout := shiftin(0);
    when shiftin_33   => carryout := shiftin(33);
    when shiftin_32   => carryout := shiftin(32);
    when shiftin_prev => 
    when others => null;
  end case;
    
  shieftout := shiftin(32 downto 1);
  shieftcarryout := carryout;
  
end;

end armshiefter;