37_test_105.vhd

VHDL语言100例详解

--Page          :308,309

--Objective     :Function slices

--Filename      :test_105.vhd

--Author        :Joseph Pick

entity Test_105 is

end Test_105;

architecture Behave_1 of Test_105 is

  type Logic4 is ('x','0','1','z');
  type Logic4_Vector is array (NATURAL range <> ) of Logic4;
  type Logic4_Table is array ( Logic4,Logic4) of Logic4;

  constant Sample_Tb1 : Logic4_Table := (('x','x','1','x'),
										 ('x','0','1','z'),
										 ('1','1','1','1'),
										 ('x','z','1','z'));

  function Manipulate_Vectors(L_V,R_V : Logic4_Vector)
				return Logic4_Vector is

     alias L_V_Alias : Logic4_Vector(L_V'LENGTH downto 1) is L_V;
     alias R_V_Alias : Logic4_Vector(R_V'LENGTH downto 1) is R_V;
     variable Result : Logic4_Vector(L_V'LENGTH downto 1);

  begin 

	for I in Result'RANGE loop
	  Result(I) := Sample_Tb1(L_V_Alias(I), R_V_Alias(I));
    end loop;

	return Result;

  end Manipulate_Vectors;
				  
	  signal Vector_A : Logic4_Vector(0 to 7);
	  signal Vector_B : Logic4_Vector(0 to 7);
	  signal Vector_C : Logic4_Vector(0 to 7);
  begin

	Funct_Slice_Test:
	process 
	  --variable Vector_A : Logic4_Vector(0 to 7);
	  --variable Vector_B : Logic4_Vector(0 to 7);
	  --variable Vector_C : Logic4_Vector(0 to 7);
    begin
	  Vector_A <= "xxx1z1x1";
	  Vector_B <= "111100x0";
	  Vector_C <= Manipulate_Vectors(Vector_A,Vector_B);
	  --Following line should result in a run_time errorr
	  --due to the fact that the function slice has an ascending 
	  --range whereas the returned result is declared 
	  --to have a descending one .
	  --Vector_C := Manipulate_Vectors(Vector_A,Vector_B)(4 downto 1);

	  --Following line result in a run_time error due to the fact
	  --element result(0) does not exist.
	  --Vector_C := Manipulate_Vectors(Vector_A,Vector_B)
	  --					 (4 downto 1);
	  wait for 50 ns;
	end process Funct_Slice_Test;

	Finish:
	process
	begin
		wait for 400 ns;
		assert false
		report "--------End of Simulation--------"
		severity error;
	end process Finish;


end Behave_1;