According to Apple it's for a method and apparatus embodied in transaction layer software suitable for use with serial bus devices, such as IEEE standard 1394 serial bus devices for supporting multiple link device drivers. The invention acquires or otherwise ascertains the capabilities of link devices and provides link device driver configurations to such link devices based on the link device's capabilities and behaviors, among other factors.

Here's Apple's summary of the invention: "The present invention is a method and apparatus embodied in transaction layer software suitable for use with serial bus devices, such as IEEE standard 1394 serial bus devices for supporting multiple link device drivers. In its most general terms, the invention acquires or otherwise ascertains the capabilities of link devices and provides link device driver configurations to such link devices based on the link device's capabilities and behaviors, among other factors.

"The invention further relates to machine readable media on which are stored embodiments of the present invention. It is contemplated that any media suitable for retrieving instructions is within the scope of the present invention. By way of example, such media may take the form of magnetic, optical, or semiconductor media. The invention also relates to data structures that contain embodiments of the present invention, and to the transmission of data structures containing embodiments of the present invention. The method and operation of the invention may be carried out by a conventional processor within the serial bus device as is known in the art.

"In general the invention may be used to configure one or more link device drivers in a module of a serial bus device according to the capabilities of the link devices, the behavior of the link devices, and other criteria.

"In a first system embodiment, the invention operating in the transaction layer of the module is operatively coupled for communication to one or more link devices for the configuration of the link device drivers for the link devices. In a second system embodiment, the invention operating in the transaction layer of the module is operatively coupled for communication to a device driver service which is operatively coupled for communication with one or more link devices. The device driver service provides messaging between the transaction layer and the link devices for the configuration of the link device drivers. In general, the invention and the link devices communicate via driver control commands.

"The link devices which for which the invention provides link driver configuration may comprise the same or different types. In cases where the link devices are the same type, the invention configures the link driver for each link device according to the behavior of the link device (e.g., the type of communication carried out by the link device) as well as the capabilities of the link device. For example, in a module having first and second nodes, each node having a link device, first node may be configured for asynchronous communication, while the second node may be configured for isochronous communication. Even though the link device in the first node is identical to the link device in the second node, the invention may provide link driver configuration optimized for asynchronous data transfer to the link device in the first node and link driver configuration optimized for isochronous data transfer to the link device in the second node to thereby support the behavior carried out by each respective module.

"Other criteria may be used to configure link devices including, for example, user defined input criteria provided by a user of the module.

"In operation, during initialization, link drivers are "installed" or loaded according to the type of system involved. For embedded systems, the method for installing device drivers will vary depending on the needs of the implementation. Device drivers for locally resident drivers may be pre-compiled into a ROM image. Under this arrangement, at boot time the drivers would be called to perform initialization thereof.

"The transaction layer software of the present invention then queries each of the link drivers to ascertain each link device's capabilities via a driver control command. In the preferred embodiment, the transaction layer requests the link's capabilities as soon as it becomes aware of the link device. In response, the link drivers transmit its respective capabilities to the transaction layer software. The capabilities of the link device may be staticly provided in a resident storage device, such as a BIOS (basic input/output system), for example. The transaction layer software may receive additional configuration data such as user-defined configuration, which may define specific behaviors of the module. The transaction layer software then generates link driver configuration data according to the link device capabilities and the other configuration data for each link device. The generated link driver configuration is then transmitted to the respective link device driver and loaded therein."

The inventor is Steven W. Brown. The graphic below is a functional block diagram of serial device module.