Use clause

Another new provision in Section 271 provides that a patented invention, if substantially completed within the United States and then finally completed elsewhere, cannot avoid infringement of the U.S. patent. This is a useful clause because a recent U.S. court decision had held that all aspects of a patented invention must be practiced within the United States in order to infringe the U.S. patent. It now remains for the courts to decide what is meant by substantially completed. ... 

In those countries where such experimental use clauses are not in force, as is the case in much of Europe, there is normally no such rapid onset of competition when patents expire, and often the innovator product enjoys another 2 to 3 years monopoly, until generics products make it to the market. This also allows the innovator company to start marketing its own generic product, and thus benefit from the first-entry advantage in order to achieve generic market share, before competitors reach the market [19]. 

Normally, manufacturers notify the certifying authority regarding the issuance of the certificates. The certifying authority checks that all the requirements of the standard are met (see Clause 1.4 of Chapter VIII), and issues the certificates. As per lEC 61511, users can develop other criteria for certifying SIS loop components including requirements for the selection of components and subsystems based on prior use (Clause 11.5.3 of the standard). The main issue here is the appropriate evidence for subsystems and components that these are suitable for safety instrumentation. The standard also specifies the required documentation pertinent to the following issues mainly (see Clause 1.4 of Chapter VIII) ... 

The purpose of the proven-in-use clause in lEC 61508 is to allow existing products that have appropriate field experience to use the field experience as an alternative means of meeting the systematic requirements. The purpose of Prior Use lEC 61511 is also to allow existing products that have appropriate field experience to use the field experience as an alternative means of meeting either or both the random hardware failure rate/PFD and/or the systematic requirements. 

Your VHDL design instantiates a component "SUB" from the technology libraiy. The component declaration of the component "SUB" is in a package "comps which is made visible by the use clause. I get this error during read. 

Identifier is not visible because it is ambiguous (homographs were introduced by USE clauses). (VSS-574)... 

It may also contain use clauses, subprogram bodies and attribute specifications. A number of other items are not supported for syn-thesis. All items in the declarative part are also visible to any architecture that uses the entity. Each declaration is discussed in this or later diapters. 

It may also contain use clauses (section 3.4.3) and attribute specifications. A niunber of other items are not supported for syndesis. 

If a use clause is located inside a declarative part of, say, a process, then the specified package contents are visible only to that process. The use clause can be placed in any declarative part to provide this local visibility. 

This will include the library in the design. To make some or all items contained within a package visible to a design unit, the library containing the package must first be included and then a use clause is required. This has the following syntax ... 

Items (declaration, subprogram, etc.) can be accessed directly from a library or package without using a library clause or use clause. To access a particular item within a particular package/library, just refer to the item using an appropriate logical prefix (defined above), creating a selected name viz. ... 

In this case no library or use clauses would be required. The syntax of these clauses is illustrated in Box 3.14. 

The first stage is to select the libraries that the design is to use. The basic libraries and packages that are available to a VHDL designer have been discussed in Chapter 3. This example uses objects of type BIT and BIT VECTOR, and executes basic logic operations. It therefore only requires the STD library with its STANDARD package. As these are implicitly visible to every design unit. Library and Use clauses are not required. 

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... 

No library or use clause indicates that the synthesized components... 

It may also contain subprogram bodies. Use clauses and attribute specifications. 

The new packages are stored in a library called USER UTILS. The NEW TYPE DEFS package must be made visible to each design imit by using Library and Use clauses. The procedure PRESET CLEAR is only used in the architecture SYNC WAIT. 

The identifiers given in the Use clauses are all item specific. Hence, only the two required operator functions in the BIT ARITH package and the clock function in the BIT UTILS package are visible. 

The function declarative part may contain declarations for subprograms, types, subtypes, constants, variables, attributes. It may also contain subprogram bodies, attribute specifications and use clauses. Several other declarations are not supported for synthesis. Every declaration made in this part is reset between calls. Initial values for objects will be ignored when synthesizing. 

This ardiitecture also illustrates the use of Selected names to access libraries and packages. The ARITH library contains the compiled package ARITH TYPES and to access the SIGNED type declaration the Library and Use clauses have been used in the normal way. To access the operator function a Selected name has been used. This directly selects the library, package and function without the need for a Use clause. Section 3.4.3 discussed accessing package items in this way. 

The third architecture RIPPLES takes this direct access a step further and dispenses with the Use clause altogether. Both the SIGNED type declaration and the RIPPLE function are accessed directly. This architecture accesses the second RIPPLE function, overloading the first by the number of parameters that are supplied. This is only one way of achieving function overloading Box 6.8 discusses these methods further. Another approach selects the appropriate function by the type of the parameters that are supplied. 

Usually, supported attributes are provided in a package. This will contain the Attribute Declaration statement for each attribute. Having made this package visible through a Use clause. Attribute Specification statements associate or decorate an item with the attribute and value. For example, if the... 

The adder itself is a procedure called RC ADDER contained in the package ARITH UTILS. This is accessed as usual through a Use clause. 

ISA S84.01 has these useful clauses describing the hazard study stages ... 

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