VHDL Programming

Advanced Topics 219

ATTRIBUTE location : INTEGER;

END p_attr;

USE WORK.p_attr.ALL;

ENTITY board IS

PORT(

.

.

.

);

END board;

ARCHITECTURE cpu_board OF board IS

COMPONENT mc68040

GENERIC(...... );

PORT(

.

.

.

);

END COMPONENT;

SIGNAL a : INTEGER;

SIGNAL b : t_package_type;

ATTRIBUTE package_type OF mc68040 : COMPONENT IS pin_grid;

ATTRIBUTE location OF mc68040 : COMPONENT IS 20;

BEGIN

a <= mc68040’location;

-- returns 20

b <= mc68040’package_type;

-- returns pin_grid

END cpu_board;

This is a very simple example of how attributes can be attached to

objects. Much more complicated types and attributes can be created. What

this example shows is a code fragment of a CPU board design in which

the package type and location information are specified as attributes of

the single microprocessor used in the design.

The package_typeattribute is used to hold the kind of packaging

used for the microprocessor. Attributes that have values specified do not

have to be used in the simulation. Other tools such as physical layout

tools or fault simulation can make use of attributes that a logic simu-

lator cannot.

In this example, a physical layout tool could read the package type

information from the package_typeattribute and, based on the value

assigned to the attribute, fill in the value for the location attribute.