Modern instruments typically possess much more functionality than is represented in the IVI instrument class specifications. End users must have a way to access the full capability of the instrument they have purchased. Thus, the driver must expose interfaces that are specific to that instrument alone. These are known as instrument-specific capabilities.
Instrument-specific capabilities are obviously not interchangeable. End users programming against a driver's instrument-specific interfaces typically do so to access functionality that is not available in the class-compliant interfaces . Nevertheless, for complex instruments such as spectrum analyzers, there will often be far more functionality in the IVI driver's instrument-specific hierarchy than in the class-compliant hierarchy.
Although, by definition, IVI does not dictate the syntax and semantics of instrument-specific interfaces, there are still guidelines that must be followed in the design of the interfaces if the driver is to be IVI compliant. Most of these rules are laid out in IVI-3.4: API Style Guide.
