Package declaration

A package declares names and asserts facts about those names. The declarations and facts may be in pictorial form. A package has an associated dictionary or narrative (or... 

Composition of the Test Products, as far as Known or Readable from the Packaging Declaration... 

The expression specifies the value of the constant. It is only optional when making the constant declaration inside a package declaration. In this case, the value of the deferred constant must be assigned in the associated package body. 

A package is used to store elements of a design that are frequently used or common to several design units. Package declarations and package bodies are themselves design units which can make use of the resources available in other packages. 

Resource libraries generally fall into two types. The first are those that are predefined and provided by synthesis tool or CAE vendors. These primarily contain package declarations and bodies of the sort described in section 3.4.1. The second type are user defined. These may be previous circuit designs which have design tmits that are common to the present one or simply contain declarations that the designer frequently uses. User-defined libraries may therefore contain not only packages but also entities and architectures. 

A package declaration is used to store frequently used declarations and subprograms. It has the syntax ... 

As with an entity s declarative part, the package declarative part may contain dedarations for any of the following items ... 

All items in the package declarative part are visible to any package body that uses the package declaration. 

The items in a package declaration and package body (if any) are visible to any oti er design unit whidi has been given explidt access through a use dause. 

A package body cannot exist without a package declaration. 

The package declaration and package body are also a pair of design units that enable frequently used declarations to be stor in common groups,... 

In each case, the ccnnponents that are used must be declared and instantiated. A component declaration informs the architecture that a particular component is being used and lists its inputs and outputs. The declaration may be located in the architecture s declarative part or a package declaration. It is possible to omit the declaration and instantiate the entity and architecture of the component directly (Box 4.6). 

The entity declaration and architecture body of each component is shown in Figure 4.9. Again these descriptions are compiled and stored in the working library where the multiplexer architecture, STRUCTURAL2, can access them. Unlike STRUCTURAL , however, this architecture does not declare the components in its declarative part. Instead it uses a package declaration to store the component declarations. A Use clause is then required to... 

The STANDARD package declares shift operators for one-dimensional arrays with elements of type BIT and BOOLEAN. The following operators are available ... 

Functions are usually stored in packages. The function declaration is stored in the package declaration and the function body in the package body. A declaration is not required for the function if its body is located in the declarative part of an entity, architecture, procediure or another function. The visibility of the function is however restricted in any of these cases. 

A procedure is a subprogram that can receive and return any number of values. Like a function, it can consist of both a separate declaration and a body. When storing the procedure in a package, the procedure declaration is placed in the package declaration and die procedure body is stored in the package body. The syntax for both statements is ... 

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