Apple, Inc. v. Motorola, Inc. et al

Filing 12

AMENDED COMPLAINT for Patent Infringement against Motorola Mobility, Inc., Motorola, Inc., filed by Apple, Inc.. (Attachments: # 1 Exhibit A - '949 patent, # 2 Exhibit B - '002 patent, # 3 Exhibit C - '315 patent, # 4 Exhibit D - RE '486 patent, # 5 Exhibit E - '354 patent, # 6 Exhibit F - '263 patent, # 7 Exhibit G - '983 patent, # 8 Exhibit H - '705 patent, # 9 Exhibit I - '647 patent, # 10 Exhibit J - '852 patent, # 11 Exhibit K - '131 patent, # 12 Exhibit L - '337 patent, # 13 Exhibit M - '867 patent, # 14 Exhibit N - '721 patent, # 15 Exhibit O - '599 patent) (Peterson, James) [Transferred from Wisconsin Western on 12/1/2011.]

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EXHIBIT K 111111111111111111111111111111111111111111111111111111111111111111111111111 US005915131A United States Patent [19] [11] Knight et al. [54] [45] 5,553,245 5,572,675 METHOD AND APPARATUS FOR HANDLING I/O REQUESTS UTILIZING SEPARATE PROGRAMMING INTERFACES TO ACCESS SEPARATE I/O SERVICES [73] Assignee: Apple Computer, Inc., Cupertino, Calif. [21] Appl. No.: 08/435,677 [22] Filed: May 5, 1995 6 Int. C1. U.S. Cl. G06F 9/40; G06F 13/14 395/892; 395/682; 395/828; 395/702; 707/104; 345/333 Field of Search 395/828, 702, 395/834, 200.2, 892, 682, 309; 345/333; 707/104 [56] References Cited 6/1986 2/1988 3/1990 1/1991 7/1992 9/1992 3/1993 7/1995 2/1996 4/1996 7/1996 7/1996 Castel et al. Nichols Bennett et al. Tignor et al. Coyle, Jr. et al. Basso et al. Lary et al. Rimmer et al. Bondy et al. Cook et al. Feeney et al. Taylor et al. l 364/200 370/85 380/10 364/200 395/650 395/325 395/425 395/275 395/500 395/800 395/834 379/201 [57] BLOCK STORAGE API A computer system handling multiple applications wherein groups of I/O services are accessible through separate application programming interfaces. Each application has multiple application programming interfaces by which to access different families of I/O services, such as I/O devices. 20 Claims, 8 Drawing Sheets f-- SCSI MANAGER API io3 io2 J 204 USER MODE WORLD KERNEL WORLD 11 2?5 ~6 FILE MANAGER FPISERVER 2 08 BLOCK STORAGE FPISERVER FILE MANAGER FAMILY ~ HFS FILE SYSTEM BLOCK STORAGE ~L- 395/284 395/200.2 ABSTRACT APPLICATION 201 FILE f-MANAGER API 9/1996 Su et al. 11/1996 Bergler Primary Examiner-Thomas C. Lee Assistant Examiner-Rehana Perveen Attorney, Agent, or Firm-Blakely, Sokoloff, Taylor & Zafman U.S. PATENT DOCUMENTS 4,593,352 4,727,537 4,908,859 4,982,325 5,129,086 5,148,527 5,197,143 5,430,845 5,491,813 5,513,365 5,535,416 5,537,466 Jun. 22, 1999 Forin, A., et al. entitled "An I/O System for Mach 3.0," Proceedings of the Usenix Mach Symposium 20-22, Nov. 1991, Monterey, CA, US, 20-22 Nov. 1991, pp. 163-176. Steve Lemon and Kennan Rossi, entitled "An Object Oriented Device Driver Model," Digest of Papers Compcon '95, Technologies for the Information Superhighway 5-9, Mar. 1995, San Francisco, CA, USA pp. 360-366. Glenn Andert, entitled "Object Frameworks in the Taligent OS," Intellectual Leverage: Digest of Papers of the Spring Computer SOCI International Conference (Compcon), San Francisco, Feb. 28-Mar. 4, 1994, Feb. 24, 1994, Institute of Electrical and Electronics Engineers, pp. 112-121. Hu, 'Interconnecting electronic mail networks: Gateways and translation strategies are proposed for backbone networks to interchange incompatible electronic documents on multivendor networks', Data Communications, p. 128, vol. 17, No. 10, Sep. 1988. Knibbe, 'IETF's Resource Reservation Protocol to facilitate mixed voice, data, and video nets', Network World, p. 51, Apr. 24, 1995. Inventors: Holly N. Knight, La Honda; Carl D. Sutton, Palo Alto; Wayne N. Meretsky, Los Altos; Alan B. Mimms, San Jose, all of Calif. [58] 5,915,131 OTHER PUBLICATIONS [75] [51] [52] Patent Number: Date of Patent: ~ DISK DRIVER tl-- 11 207 SCSI MANAGER FPISERVER SCSI MANAGER FAMILY ~ SIM 109 121 DISPLAY HARD COPY DEVICE 124 LAN 108 MODEM 107 MASS STORAGE '\r-- ,A-- - /'-- ~ r lr--1- ~ SOUND CHIP 125 / 1/0 BUS 101 FLOPPY DISK DRIVE 126 ) ) I-- / 181 ~ ) n FIG. 1 TEMP. SENSOR CURSOR CONTROL 123 J I I CLK t LOCAL B~100 I DECODER 154 1~7A 184 TO CLOCK GENERATOR 160 ~ MICROCONTROLLER 127 BUS TRANSLATOR! INTERFACE UNIT 140 ~ SIGNAL 182 POW~ r-... KEYBOARD 122 1/0 CONTROLLER 130 TIMER 150 ~ CLK , I VDD SWITCH 153 COMPONENTS TO OTHER HOT INDICATION ) SIGNAL 183 POWER SUPPLY 1521] "'- 160 CLOCK GENERATOR .. FROM I '0 INTERFJ E 140 NON-VOLATILE MEMORY 106 MAIN MEMORY 104 PROCESSOR 103 V DD '.4- d = =- ~ ~ ~ Ul .... ~ \C Ul .... QIO '" o"'" ...., .... ~ ~ 'JJ. '""'" '0 '0 '0 ~N N ? ~ = ~ ~ ..... ..... ~ • 'JJ. • u.s. Patent 5,915,131 Sheet 2 of 8 Jun. 22, 1999 APPLICATION 201 FILE MANAGER API L- BLOCK I-I-SCSI STORAGE MANAGER API API I '. 203 204 USER MODE WORLD I-- "" io2 KERNEL WORLD !1 2?5 FILE MANAGER FPISERVER BLOCK STORAGE FPISERVER FILE MANAGER FAMILY BLOCK STORAGE FAMILY ~ ~ 208 L- HFS FILE SYSTEM { I- L- !7 2»6 DISK DRIVER l FIG. 2 I- 297 SCSI MANAGER FPISERVER SCSI MANAGER FAMILY ~ '- SIM I- u.s. Patent Jun. 22, 1999 Sheet 3 of 8 5,915,131 APPLICATION 302 P_R_O_C_E_D_U_R_Er-C_A_L_L......l:~ _~ _ __ IFPI~~:ARYI ~~~~~AMMING ~~~ERFACE KERNEL MESSAGE USER MODE WORLD KERNEL MESSAGE KERNEL WORLD FPISERVER 304 PROCEDURE CALL -lor FAMILY: 305 PROCEDURE CALL PLUG-IN _______________ PROGRAMMING INTERFACE PLUG-IN 306 307 FIG. 3 u.s. Patent Xlib u Jun. 22, 1999 5,915,131 Sheet 4 of 8 ~ ~4 ~5 Zlib u USER MODE WORLD ~) X FPI SERVER 401 ...... Y FPI SERVER 408 KERNEL WORLD 409 X 411 Y 412 r------>o~1"'--___,1-., Z FPI SERVER 410 Z 413 X FAMILY IMPLEMENTATION Z FAMILY IMPLEMENTATION 414 ~ 416 ~ Z X '- PLUG IN - '- PLUG IN - ../ 417 419 FIG.4 403 u.s. Patent Sheet 5 of 8 Jun. 22, 1999 5,915,131 Dlib u 503 USER MODE WORLD KERNEL WORLD Z FPI SERVER z Z FAMILY IMPLEMENTATION ~ Z . 502 / r---~---. D FPI J...-=';- SERVER D 505 '- PLUG IN "-...I-_----Ir ~ 501 ;:===~=======::::=.J FIG. 5 504 u.s. Patent Jun. 22, 1999 5,915,131 Sheet 6 of 8 FAMILY FAMILY A B SHARED CODE AND/OR DATA 601 602 FIG. 6 u.s. Patent Jun. 22, 1999 Sheet 7 of 8 5,915,131 APPLICATION 710 ~ 711 APls IV USER MODE WORLD KERNEL WORLD 7~ v ~ FPI SERVER 7~ > ACCEPT FUNCTION STREAMS ~ WORLD IPROTOCOL I IPROTOCOL I IPROTOCOL I ? ~ NETWORK DEVICE ~,./ DRIVER FIG. 7 > SINGLE TASK u.s. Patent Jun. 22, 1999 Sheet 8 of 8 5,915,131 APPLICATION a01 ~ API a02 P --~- USER MODE WORLD KERNEL WORLD 803 FPISERVER FAMILY 804 WRAPPER TASK FIG. 8 5,915,131 1 2 METHOD AND APPARATUS FOR HANDLING I/O REQUESTS UTILIZING SEPARATE PROGRAMMING INTERFACES TO ACCESS SEPARATE I/O SERVICES FIG. 1 a block diagram of one embodiment in the computer system of the present invention. FIG. 2 is an overview of the I/O architecture of the present invention. FIG. 3 illustrates a flow diagram of I/O service request handling according to the teachings of the present invention. FIG. 4 illustrates an overview of the I/O architecture of the present invention having selected families accessing other families. FIG. 5 illustrates extended programming family interface of the present invention. FIG. 6 illustrates plug-in modules of different families that share code and/or data. FIG. 7 illustrates a single task activation model according to the teachings of the present invention. FIG. 8 illustrates a task-per-plug-in model used as an activation model according to the teachings of the present invention. 5 FIELD OF THE INVENTION The invention relates to the field of computer systems; particularly, the present invention relates to handling service requests generated by application programs. 10 BACKGROUND OF THE INVENTION Application programs running in computer systems often access system resources, such as input/output (I/O) devices. These system resources are often referred to as services. Certain sets of services (e.g., devices) have similar characteristics. For instance, all display devices or allADB devices have similar interface requirements. To gain access to I/O resources, applications generate service requests to which are sent through an application programming interface (API). The service requests are converted by the API to a common set of functions that are forwarded to the operating system to be serviced. The operating system then sees that service requests are responded to by the appropriate resources (e.g., device). For instance, the operating system may direct a request to a device driver. One problem in the prior art is that service requests are not sent directly to the I/O device or resource. All service requests from all applications are typically sent through the same API. Because of this, all of the requests are converted into a common set of functions. These common set of functions do not have meaning for all the various types of I/O devices. For instance, a high level request to play a sound may be converted into a write function to a sound device. However, the write function is not the best method of communicating sound data to the sound device. Thus, another conversion of write data to a sound data format may be required. Also, some functions do not have a one-to-one correspondence with the function set of some I/O devices. Thus, it would be desirable to avoid this added complexity and to take advantage of the similar characteristics of classes of I/O devices when handling I/O requests, while providing services and an environment in which to run those services that is tuned to the specific device needs and requirements. 15 20 DETAILED DESCRIPTION OF THE PRESENT INVENTION 25 30 35 40 45 SUMMARY OF THE INVENTION A method and apparatus for handling I/O requests is described. In the present invention, the I/O requests are handled by the computer system having a bus and a memory coupled to the bus that stores data and programming instructions. The programming instructions include application programs and an operating system. A processing unit is coupled to the bus and runs the operating system and application programs by executing programming instructions. Each application programs have multiple separate programming interfaces available to access multiple sets of I/O services provided through the operating system via service requests. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only. 50 55 60 65 A method and apparatus handling service requests is described. In the following detailed description of the present invention numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention. Some portions of the detailed descriptions which follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. The present invention also relates to apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may 5,915,131 3 4 comprise a general purpose computer selectively activated selections to processor 103, and a cursor control 123, such or reconfigured by a computer program stored in the comas a trackball, stylus, mouse, or trackpad, etc., for controlling cursor movement. The system also includes a sound puter. The algorithms and displays presented herein are not chip 125 coupled to I/O controller 130 for providing audio inherently related to any particular computer or other apparatus. Various general purpose machines may be used with 5 recording and play back. Sound chip 125 may include a sound circuit and its driver which are used to generate programs in accordance with the teachings herein, or it may various audio signals from the computer system. I/O conprove convenient to construct more specialized apparatus to troller 130 may also provide access to a floppy disk and perform the required method steps. The required structure for a variety of these machines will appear from the descripdriver 126. The processor 103 controls I/O controller 130 tion below. In addition, the present invention is not 10 with its peripherals by sending commands to I/O controller 130 via local bus 100, interface unit 140 and I/O bus 101. described with reference to any particular programming language. It will be appreciated that a variety of programBatteries or other power supply 152 may also be included to provide power necessary to run the various peripherals ming languages may be used to implement the teachings of and integrated circuits in the computer system. Power supthe invention as described herein. Overview of the Computer System of the Present Invention 15 ply 152 is typically a DC power source that provides a constant DC power to various units, particularly processor Referring to FIG. 1, an overview of a computer system of the present invention is shown in block diagram form. The 103. Various units such as processor 103, display 121, etc., present invention may be implemented on a general purpose also receive clocking signals to synchronize operations microcomputer, such as one of the members of the Apple within the computer systems. These clocking signals may be family of personal computers, one of the members of the 20 provided by a global clock generator or multiple clock generators, each dedicated to a portion of the computer IBM personal computer family, or one of several other computer devices which are presently commercially availsystem. Such a clock generator is shown as clock generator able. Of course, the present invention may also be imple160. In one embodiment, clock generator 160 comprise a mented on a multi-user system while encountering all of the phase-locked loop (PLL) that provides clocking signals to costs, speed, and function advantages and disadvantages 25 processor 103. I/O controller 140 includes control logic to coordinate the available with these machines. As illustrated in FIG. 1, the computer system of the thermal management. Several additional devices are present invention generally comprises a local bus or other included within the computer system to operate with the control logic within I/O controller 140. A timer 150, a switch communication means 100 for communicating information, a processor 103 coupled with local bus 100 for processing 30 153 and a decoder 154 are included to function in connection information, a random access memory (RAM) or other with the control logic. In one embodiment, decoder 154 is dynamic storage device 104 (commonly referred to as a included within bus interface unit 140 and timer 150 is main memory) coupled with local bus 100 for storing included in I/O controller 130. Switch 153 is a p-channel power MOSFET, which has its information and instructions for processor 103, and a readonly memory (ROM) or other non-volatile storage device 35 gate connected to the power signal 182, its source to the power supply and its drain to processor's VDD pin. 106 coupled with local bus 100 for storing non-volatile information and instructions for processor 103. In one embodiment, processor 103 is a member of the PowerPCTM family of processors, such as those manufacThe computer system of the present invention also includes an input/output (I/O) bus or other communication tured by Motorola Corporation of Schaumberg, Ill. The means 101 for communication information in the computer 40 memory in the computer system is initialized to store the operating system as well as other programs, such as file system. A data storage device 107, such as a magnetic tape directory routines and application programs, and data inputand disk drive, including its associated controller circuitry, ted from I/O controller 130. In one embodiment, the operis coupled to I/O bus 101 for storing information and ating system is stored in ROM 106, while RAM 104 is instructions. A display device 121, such as a cathode ray tube, liquid crystal display, etc., including its associated 45 utilized as the internal memory for the computer system for accessing data and application programs. Processor 103 controller circuitry, is also coupled to I/O bus 101 for accesses memory in the computer system via an address bus displaying information to the computer user, as well as a hard copy device 124, such as a plotter or printer, including within bus 100. Commands in connection with the operation its associated controller circuitry for providing a visual of memory in the computer system are also sent from the representation of the computer images. Hard copy device 50 processor to the memory using bus 100. Bus 100 also includes a bi-directional data bus to communicate data in 124 is coupled with processor 103, main memory 104, non-volatile memory 106 and mass storage device 107 response to the commands provided by processor 103 under through I/O bus 101 and bus translator/interface unit 140. A the control of the operating system running on it. modem 108 and an ethernet local area network 109 are also Of course, certain implementations and uses of the coupled to I/O bus 101. 55 present invention may neither require nor include all of the Bus interface unit 140 is coupled to local bus 100 and I/O above components. For example, in certain implementations a keyboard or cursor control device for inputting informabus 101 and acts as a gateway between processor 103 and the I/O subsystem. Bus interface unit 140 may also provide tion to the system may not be required. In other translation between signals being sent from units on one of implementations, it may not be required to provide a display the buses to units on the other bus to allow local bus 100 and 60 device displaying information. Furthermore, the computer system may include additional processing units. I/O bus 101 to co-operate as a single bus. The operating system running on processor 103 takes care An I/O controller 130 is coupled to I/O bus 101 and controls access to certain I/O peripherals in the computer of basic tasks such as starting the system, handling system. For instance, I/O controller 130 is coupled to interrupts, moving data to and from memory 104 and controller device 127 that controls access to an alpha- 65 peripheral devices via input/output interface unit 140, and managing the memory space in memory 104. In order to take numeric input device 122 including alpha-numeric and other care of such operations, the operating system provides keys, etc., for communicating information and command 5,915,131 5 6 multiple execution environments at different levels (e.g., request may be communicated from application level to the file system family, resulting in one or more requests to the task level, interrupt level, etc.). Tasks and execution enviblock storage family, and finally one or more to the SCSI ronments are known in the art. family to complete a service request. Note that in one Overview of the Present Invention In one embodiment, the computer system runs a kernel- 5 embodiment, there is no hierarchical relationship among families; all families are peers of each other. based, preemptive, multitasking operation system in which Families in the Present Invention applications and I/O services, such as drivers, operate in A family provides a distinct set of services to the system. separate protection domains (e.g., the user and kernel For example, one family may provide network services, domains, respectively). The user domain does not have while another provides access to a variety of block storage direct access to data of the kernel domain, while the kernel 10 mediums. A family is associated with a set of devices that domain can access data in the user domain. have similar characteristics, such as all display devices or all The computer system of the present invention uses one or ADB devices. more separate families to provide I/O services to the system. In one embodiment, each family is implemented in softEach I/O family provides a set of I/O services to the system. ware that runs in the computer system with applications. A For instance, a SCSI family and its SCSI interface modules 15 family comprises software that includes a family program(SIMs) provide SCSI based services, while a file systems ming interface and its associated FPI library or libraries for family and its installable file systems provide file manageits clients, an FPI server, an activation model, a family ment services. In one embodiment, an I/O family is impleexpert, a plug-in programming interface for its plug-ins, and mented by multiple modules and software routines. a family services library for its plug-ins. FIG. 3 illustrates the interaction between these compoEach family defines a family programming interface (FPI) 20 nents. Referring to FIG. 3, a family programming interface designed to meet the particular needs of that family. An FPI provides access to a given family's plug-ins, which are (FPI) 301 provides access to the family's services to one or dynamically loaded pieces of software that each provide an more applications, such as application 302. The FPI 301 also instance of the service provided by a family. For example, provides access to plug-ins from other families and to within the file systems family (File Manager), a plug-in 25 system software. That is, an FPI is designed to provide callers with services appropriate to a particular family, implements file-system-specific services. In one whether those calls originate from in the user domain or the embodiment, plug-ins are a superset of device drivers, such operating system domain. that all drivers are plug-ins, but not all plug-ins are drivers. For example, when an application generates data for a Access to services is available only through an I/O family's programming interface. In one embodiment, hard- 30 video device, a display FPI tailored to the needs of video ware is not directly accessible to application software, nor is devices is used to gain access to display services. Likewise, it vulnerable to application error. Applications have access when an application desires to input or output sound data, to hardware services only through an I/O family's programthe application gains access to a sound family of services ming interface. Also, the context within which an I/O service through an FPI. Therefore, the present invention provides runs and the method by which it interacts with the system is 35 family programming interfaces tailored to the needs of defined by the I/O family to which it belongs. specific device families. FIG. 2 illustrates the relationship between an application, Service requests from application 302 (or other several I/O families, and their plug-ins. Referring to FIG. 2, applications) are made through an FPI library 303. In one an application 201 requests services through one or more embodiment, the FPI library 303 contains code that passes family FPIs, shown in FIG. 2 as File Manager API 202, 40 requests for service to the family FPI server 304. In one embodiment, the FPI library 303 maps FPI function calls Block Storage API 203, and SCSI Manager API 204. The File Manager API 202, Block Storage API 203, and SCSI into messages (e.g., kernel messages) and sends them to the FPI server 304 of the family for servicing. In one Manager API 204 are available to one or more applications in the user domain. embodiment, a family 305 may provide two versions of its In one embodiment, the service requests from application 45 FPI library 303, one that runs in the user domain and one that 201 (and other applications) are sent through File Manager runs in the operating system kernel domain. API 202, Block Storage API 203, and/or SCSI Manager API In one embodiment, FPI server 304 runs in the kernel 204, etc., and flow as messages to family FPI servers domain and responds to service requests from family clients 205-207, which reside in the kernel domain. In one (e.g., applications, other families, etc.). FPI server 304 embodiment, the messages are delivered using a kernel- 50 responds to a request according to the activation model (not supplied messaging service. shown) of the family 305. In one embodiment, the activation Any communication method may be used to communimodel comprises code that provides the runtime environcate service requests to I/O families. In one embodiment, ment of the family and its plug-ins. For instance, FPI server kernel messaging is used between the FPI libraries and the 304 may put a request in a queue or may call a plug-in FPI server for a given family, between different families, and 55 directly to service the request. As shown, the FPI server 304 between plug-ins of one family and another family. The forwards a request to the family 305 using a procedure call. communication method used should be completely opaque Note that if FPI library 303 and the FPI server 304 use kernel to a client requesting a family service. messaging to communicate, the FPI server 304 provides a Each of the FPI servers 205-207 permit access to a message port. Each family 305 includes an expert (not shown) to distinct set of services. For example, File Manager FPI 60 maintain knowledge of the set of family devices. In one server 205 handles service for the file manager family of services. Similarly, the Block Storage FPI server 206 embodiment, the expert comprises code within a family 305 handles service requests for the block storage family of that maintains knowledge of the set of family plug-ins serVIces. within the system. At system startup and each time a change Note that FIG. 2 shows three families linked by kernel 65 occurs, the expert is notified. In one embodiment, the expert may maintain the set of messages. Messages flow from application level through a family to another family, and so on. For instance, a service family services using a central device registry in the system. 5,915,131 7 8 The expert scans the device registry for plug-ins that belong system and block storage plug-ins are not drivers (in that to its family. For example, a display family expert looks for drivers back hardware). display device entries. When a family expert finds an entry Applications, plug-ins from other I/O families, and other system software can request the services provided by a for a family plug-in, it instantiates the plug-in, making it available to clients of the family. In one embodiment, the 5 family's plug-ins through the family's FPI. Note also that system notifies the family expert on an ongoing basis about plug-ins are designed to operate in the environment set forth new and deleted plug-ins in the device registry. As a result, by their family activation model. the set of plug-ins known to and available through the family In one embodiment, a plug-in may comprises two code remains current with changes in system configuration. sections, a main code section that runs in a task in the kernel Note that family experts do not add or alter information in 10 domain and an interrupt level code section that services the device registry nor do they scan hardware. In one hardware interrupts if the plug-in is, for instance, a device embodiment, the present invention includes another level of driver. In one embodiment, only work that cannot be done at task level in the main code section should be done at families (i.e., low-level families) whose responsibility is to interrupt level. In one embodiment, all plug-ins have a main discover devices by scanning hardware and installing and removing information for the device registry. These low- 15 code section, but not all have interrupt level code sections. level families are the same as the families previously disThe main code section executes and responds to client cussed above (i.e., high level family) in other ways, i.e. they service requests made through the FPI. For example, sound have experts, services, an FPI, a library, an activation model family plug-ins respond to sound family specific requests and plug-ins. The low-level families' clients are usually such as sound playback mode setting (stereo, mono, sample other families rather than applications. In one embodiment, 20 size and rate), sound play requests, sound play cancellation, etc. The interrupt level code section executes and responds families are insulated from knowledge of physical connecto interrupts from a physical device. In one embodiment, the tivity. Experts and the device registry are discussed in more detail below. interrupt level code section performs only essential A plug-in programming interface (PPI) 306 provides a functions, deferring all other work to a higher execution family-to-plug-in interface that defines the entry points a 25 levels. plug-in supports so that it can be called and a plug-in-toAlso because all of the services associated with a parfamily interface that defines the routines plug-ins call when ticular family are tuned to the same needs and requirements, the drivers or plug-ins for a given family may be as simple certain events, such as an I/O completion, occur. In addition, as possible. PPI 306 defines the path through which the family and its plug-in exchange data. 30 Family Programming Interfaces A family services library (not shown) is a collection of In the present invention, a family provides either a userroutines that provide services to the plug-ins of a family. The mode or a kernel-mode FPI library, or both, to support the family's FPI. FIG. 4 illustrates one embodiment of the I/O services are specific to a given family and they may be layered on top of services provided by the kernel. Within a architecture of the present invention. Referring to FIG. 4, family, the methods by which data is communicated, 35 three instances of families 401-403 are shown operating in memory is allocated, interrupts are registered and timing the kernel environment. Although three families are shown, services are provided may be implemented in the family the present invention may have any number of families. In the user mode, two user-mode FPI libraries, Xlib u 404 services library. Family services libraries may also maintain state information needed by a family to dispatch and manage and Zlib u 405, are shown that support the FPIs for families requests. 40 X and Z, respectively. In the kernel environment, two For example, a display family services library provides kernel-mode FPI libraries, Ylib k 406 and Zlibk , 407, for routines that deal with vertical blanking (which is a concern families Y and Z, respectively, are shown. Both the user-mode and the kernel-mode FPI libraries of display devices). Likewise, SCSI device drivers manipupresent the same FPI to clients. In other words, a single FPI late command blocks, so the SCSI family services library contains routines that allow block manipulation. A family 45 is the only way family services can be accessed. In one embodiment, the user-mode and kernel mode libraries are services library that provides commonly needed routines simplifies the development of that family's plug-ins. not the same. This may occur when certain operations have meaning in one mode and not the other. For example, Through the PPI 306, a call is made to a plug-in 307. In operations that are implemented in the user-mode library, one embodiment, a plug-in, such as plug-in 307, comprises dynamically loaded code that runs in the kernel's address 50 such as copying data across address-space boundaries, may space to provide an instance of the service provided by a be unnecessary in the kernel library. family. For example, within the file systems family, a plug-in In response to service requests, FPI libraries 404 and 405 map FPI functions into messages for communication from implements file-system-specific services. The plug-ins the user mode to the kernel mode. In one embodiment, the understand how data is formatted in a particular file system such as HFS or DOS-FAT. On the other hand, it is not the 55 messages are kernel messages. responsibility of file systems family plug-ins to obtain data The service requests from other families are generated by plug-ins that make calls on libraries, such as FPI libraries from a physical device. In order to obtain data from a 406 and 407. In one embodiment, FPI libraries 406 and 407 physical device, a file system family plug-in communicates map FPI functions into kernel messages and communicate to, for instance, a block storage family. In one embodiment, block storage plug-ins provide both media-specific drivers, 60 those messages to FPI servers such as Y FPI server 409 and such as a tape driver, a CD-ROM driver, or hard disk driver, Z FPI server 410 respectively. Other embodiments may use and volume plug-ins that represent partitions on a given mechanisms other than kernel messaging to communicate physical disk. Block storage plug-ins in turn may make SCSI information. family API calls to access data across the SCSI bus on a In the example, the Z family 403 has both a user-mode physical disk. Note that in the present invention, plug-ins are 65 library 405 and a kernel-mode library 407. Therefore, the a superset of device drivers. For instance, plug-ins may services of the Z family may be accessed from both the user include code that does not use hardware. For instance, file mode and the kernel mode. 5,915,131 9 10 In response to service request messages, X FPI server 408, Y FPI server 409 and Z FPI server 410 dispatch requests for services to their families. In one embodiment, each of FPI servers 408-410 receives a kernel message, maps the message into a FPI function called by the client, and then calls the function in the family implementation (414-416). In one embodiment, there is a one-to-one correspondence between the FPI functions called by clients and the function called by FPI servers 408-410 as a result. The calls from FPI serves 408-410 are transferred via interfaces 411-413. For instance, X interface 411 represents the interface presented to the FPI server 408 by the X family 414. It is exactly the same as the FPI available to applications or other system software. The same is true ofY interface 412 and Z interface 413. The X family implementation 414 represents the family activation model that defines how requests communicated from server 408 are serviced by the family and plug-in(s). In one embodiment, X family implementation 414 comprises family code interfacing to plug-in code that completes the service requests from application 400 via server 408. Similarly, the Y family implementation 415 and Z family implementation 416 define their family's plug-in activation models. X plug-in 417, Y plug-in 418 and Z plug-in 419 operate within the activation model mandated by the family and provide code and data exports. The required code and data exports and the activation model for each family of drivers is family specific and different. Extending Family Programming Interfaces A plug-in may provide a plug-in-specific interface that extends its functionality beyond that provided by its family. This is useful in a number of situations. For example, a block storage plug-in for a CD-ROM device may provide a block storage plug-in interface required of the CD-ROM device as well as an interface that allows knowledgeable application software to control audio volume and to play, pause, stop, and so forth. Such added capabilities require a plug-inspecific API. If a device wishes to export extended functionality outside the family framework, a separate message port is provided by the device and an interface library for that portion of the device driver. FIG. 5 illustrates the extension of a family programming interface. Referring to FIG. 5, a plug-in module, Z plug-in 501, extends beyond the Z family boundary to interface to family implementation D 502 as well. A plug-in that has an extended API offers features in addition to those available to clients through it's family's FPI. In order to provide extra services, the plug-in provides additional software shown in FIG. 5 as an interface library Dlib u 503, the message port code D FPI server 504, and the code that implements the extra features D 505. Sharing Code and Data Between Plug-ins In one embodiment, two or more plug-ins can share data or code or both, regardless of whether the plug-ins belong to the same family or to different families. Sharing code or data is desirable when a single device is controlled by two or more families. Such a device needs a plug-in for each family. These plug-ins can share libraries that contain information about the device state and common code. FIG. 6 illustrates two plug-ins that belong to separate families and that share code and data. Plug-ins can share code and data through shared libraries. Using shared libraries for plug-ins that share code or data allows the plug-ins to be instantiated independently without encountering problems related to simultaneous instantiation. Referring to FIG. 6, the first plug-in 601 to be opened and initialized obtains access to the shared libraries. At this point, the first plug-in 601 does not share access. When the second plug-in 602 is opened and initialized, a new connection to the shared libraries is created. From that point, the two plug-ins contend with each other for access to the shared libraries. Sharing code or data may also be desirable in certain special cases. For instance, two or more separate device drivers may share data as a way to arbitrate access to a shared device. An example of this is a single device that provides network capabilities and real time clock. Each of these functions belong to a distinct family but may originate in a single physical device. Activation Models in the Present Invention An activation model defines how the family is implemented and the environment within which plug-ins of the family execute. In one embodiment, the activation model of the family defines the tasking model a family uses, the opportunities the family plug-ins have to execute and the context of those opportunities (for instance, are the plug-ins called at task time, during privileged mode interrupt handling, and so forth), the knowledge about states and processes that a family and its plug-ins are expected to have, and the portion of the service requested by the client that is performed by the family and the portion that is performed by the plug-ins. Each model provides a distinctly different environment for the plug-ins to the family, and different implementation options for the family software. Examples of activation models include the single-task model, the task-per-plug-in model, and the task-per-request model. Each is described in further detail below. Note that although three activation models are discussed, the choice of activation model is a design choice and different models may be used based on the needs and requirements of the family. In one embodiment, the activation model uses kernel messaging as the interface between the FPI libraries that family clients link to and the FPI servers in order to provide the asynchronous or synchronous behavior desired by the family client. Within the activation model, asynchronous I/O requests are provided with a task context. In all cases, the implementation of the FPI server depends on the family activation model. The choice of activation model limits the plug-in implementation choices. For example, the activation model defines the interaction between a driver's hardware interrupt level and the family environment in which the main driver runs. Therefore, plug-ins conform to the activation model employed by its family. Single-Task Model One of the activation models that may be employed by a family is referred to herein as the single-task activation model. In the single-task activation model, the family runs as a single monolithic task which is fed from a request queue and from interrupts delivered by plug-ins. Requests are delivered from the FPI library to an accept function that enqueues the request for processing by the family's processing task and wakes the task if it is sleeping. Queuing, synchronization, and communication mechanism within the family follow a set of rules specified by the family. The interface between the FPI Server and a family implementation using the single-task model is asynchronous. Regardless of whether the family client called a function synchronously or asynchronously, the FPI server calls the family code asynchronously. The FPI server maintains a set 5 10 15 20 25 30 35 40 45 50 55 60 65 5,915,131 11 12 of kernel message IDs that correspond to messages to which the FPI server has not yet replied. The concept of maintaining kernel message IDs corresponding to pending I/O server request messages is well-known in the art; Consider as an example family 700, which uses the single-task activation model, shown in FIG. 7. Referring to FIG. 7, an application 710 is shown generating a service request to the family's APIs 711. APIs 711 contain at least one library in which service requests are mapped to FPl functions. The FPI functions are forwarded to the family's FPI server 701. FPI server 701 dispatches the FPI function to family implementation 703, which includes various protocols and a network device driver that operate as a single task. Each protocol layer provides a different level of serVIce. The FPI server 701 is an accept function that executes in response to the calling client via the FPI library (not shown). An accept function, unlike a message-receive-based kernel task, is able to access data within the user and kernel bands directly. The accept function messaging model requires that FPI server 701 be re-entrant because the calling client task may be preempted by another client task making service requests. When an I/O request completes within the family's environment, a completion notification is sent back to the FPI server 701, which converts the completion notification into the appropriate kernel message ID reply. The kernel message ID reply is then forwarded to the application that generated the service request. With a single-task model, the family implementation is insulated from the kernel in that the implementation does it not have kernel structures, IDs, or tasking knowledge. On the other hand, the relationship between FPI server 701 and family code 702 is asynchronous, and has internal knowledge of data structures and communication mechanisms of the family. The single-task model may be advantageously employed for families of devices that have one of several characteristics: (1) each I/O request requires little effort of the processing unit. This applies not only to keyboard or mouse devices but also to DMA devices to the extent that the processing unit need only set up the transfer, (2) no more than one I/O request is handled at once, such that, for instance, the family does not allow interleaving of I/O requests. This might apply to sound, for example, or to any device for which exclusive reservation is required (i.e., where only one client can use a device at a time). The opposite of a shared resource. Little effort for the processor exists where the processor initiates an I/O request and then is not involved until the request completes, or (3) the family to be implemented provides its own scheduling mechanisms independent of the underlying kernel scheduling. This applies to the Unix™ stream programming model. Task-Per-Plug-In Model For each plug-in instantiated by the family, the family creates a task that provides the context within which the plug-in operates. FIG. 8 illustrates the task-per-plug-in model. Referring to FIG. 8, an application 801 generates service requests for the family, which are sent to FPI 802. Using an FPI library, the FPI 802 generates a kernel message according to the family activation model 804 and a driver, such as plug-in driver 805. In one embodiment, the FPI server 803 is a simple task-based message-receive loop or an accept function. FPI server 803 receives requests from calling clients and passes those requests to the family code 804. The FPI server 803 is responsible for making the data associated with a request available to the family, which in turn makes it available to the plug-in that services the request. In some instances, this responsibility includes copying or mapping buffers associated with the original request message to move the data from user address space to the kernel level area. The family code 804 consists in part of one or more tasks, one for each family plug-in. The tasks act as a wrapper for the family plug-ins such that all tasking knowledge is located in the family code. A wrapper is a piece of code that insulates called code from the original calling code. The wrapper provides services to the called code that the called code is not aware of. When a plug-in's task receives a service request (by whatever mechanisms the family implementation uses), the task calls its plug-in's entry points, waits for the plug-in's response, and then responds to the service request. The plug-in performs the work to actually service the request. Each plug-in does not need to know about the tasking model used by the family or how to respond to event queues and other family mechanisms; it only needs to know how to perform its particular function. For concurrent drivers, all queuing and state information describing an I/O request is contained within the plug-in code and data and within any queued requests. The FPI library forwards all requests regardless of the status of outstanding I/O requests to the plug-in. When the client makes a synchronous service request, the FPI library sends a synchronous kernel message. This blocks the requesting client, but the plug-in's task continues to run within its own task context. This permits clients to make requests of this plug-in even while another client's synchronous request is being processed. In some cases of a family, a driver (e.g., 805) can be either concurrent or nonconcurrent. Nevertheless, clients of the family may make synchronous and asynchronous requests, even though the nonconcurrent drivers can handle only one request at a time. The device manager FPI server 803 knows that concurrent drivers cannot handle multiple requests concurrently. Therefore, FPI server 803 provides a mechanism to queue client requests and makes no subsequent requests to a task until the task signals completion of an earlier I/O request. When a client calls a family function asynchronously, the FPI library sends an asynchronous kernel message to the FPI server and returns to the caller. When a client calls a family function synchronously, the FPI library sends a synchronous kernel message to the FPI server and does not return to the caller until the FPI server replies to the message, thus blocking the caller's execution until the I/O request is complete. In either case, the behaviors of the device manager FPI server 803 is exactly the same: for all incoming requests, it either queues the request or passes it to the family task, depending on whether the target plug-in is busy. When the plug-in signals that the I/O operation is complete, the FPI server 803 replies to the kernel message. When the FPI library receives the reply, it either returns to the synchronous client, unblocking its execution or it notifies the asynchronous client about the I/O completion. The task-per-plug-in model is intermediate between the single-task and task-per-request models in terms of the number of tasks it typically uses. The task-per-plug-in model is advantageously used where the processing of I/O requests varies widely among the plug-ins. Task-Per-Request Model The task-per-request model shares the following characteristics with the two activation models already discussed: 5 10 15 20 25 30 35 40 45 50 55 60 65 5,915,131 13 14 (1) the FPI library to FPI server communication provides the sented by the entry and that contain a reference to the driver in control of the device. synchronous or asynchronous calling behavior requested by Multiple low-level experts are used, where each such family clients, and (2) the FPI library and FPI server use expert is aware of the connection scheme of p~ysical d~vic~s kernel messages to communicate I/O requests between to the system and installs and removes that mformatIOn m themselves. However, in the task-per-request model, the FPI server's interface to the family implementation is com- 5 the device tree portion of the device registry. For example a low-level expert, referred to herein as a bus expert or a pletely synchronous. motherboard expert, has specific knowledge of a piece of In one embodiment, one or more internal family request hardware such as a bus or a motherboard. Also, a SCSI bus server tasks, and, optionally, an accept function, wait for expert scans a SCSI bus for devices, and installs an entry messages on the family message port. An arriving message containing information describing an I/O request awakens 10 into the device tree for each device that it finds. The SCSI bus expert knows nothing about a particular device for one of the request server tasks, which calls a family function which it installs an entry. As part of the installation, a driver to service the request. All state information necessary to handle the request is maintained in local variables. The gets associated with the entry by the SCSI bus expert. The request server task is blocked until the I/O request driver knows the capabilities of the device and specifies that completes, at which time it replies to the kernel mess.age 15 the device belongs to a given family. This information is from the FPI library to indicate the result of the operatIOn. provided as part of the driver or plug-in descriptive structure After replying, the request server task waits for more mesrequired of all plug-ins as part of their PPI implementation. sages from the FPI library. Low-level experts and family experts use a device registry As a consequence of the synchronous nature of the notification mechanism to recognize changes in the system interface between the FPI server and the family 20 configuration and to take family-specific action in response implementation, code calling through this interface remains to those changes. running as a blockable task. This calling code is either the An example of how family experts, low-level experts, and request server task provided by the family to service the I/O the device registry service operate together to stay aware of (for asynchronous I/O requests) or the task of the requester dynamic changes in system configuration follows: Suppose of the I/O (for certain optimized synchronous requests). a motherboard expert notices that a new bus, a new network The task-per-request model is advantageously employed 25 interface and new video device have appeared within the for a family where an I/O request can require continuous system. The motherboard expert adds a bus node, a network attention from the processor and multiple I/O requests can node, and a video node to the device tree portion of the be in progress simultaneously. A family that supports dumb, device registry. The device registry service notifies all high bandwidth devices is a good candidate for this model. software that registered to receive notifications of these In one embodiment, the file manager family uses the task- 30 events. per-request model. This programming model requires the Once notified that changes have occurred in the device family plug-in code to have tasking knowledge and to use registry, the networking and video family experts scan the kernel facilities to synchronize multiple threads of execution device registry and notice the new entry belonging to their contending for family and system resources. family type. Each of the experts adds an entry in the family Unless there are multiple task switches within a family, 35 subtree portion of the device registry. the tasking overhead is identical within all of the activation The SCSI bus expert notices an additional bus, and probes models. The shortest task path from application to I/O is for SCSI devices. It adds a node to the device registry for completely synchronous because all code runs on the calleach SCSI device that it finds. New SCSI devices in the er's task thread. device registry result in perusal of the device registry by the Providing at least one level of asynchronous call between 40 block storage family expert. The block storage expert an application and an I/O request results in better latency notices the new SCSI devices and loads the appropriate results from the user perspective. Within the file system, a drivers, and creates the appropriate device registry entries, to task switch at a file manager API level allows a user-visible make these volumes available to the file manager. The file application, such as the Finder™, to continue. The file manager receives notification of changes to the block stormanager creates an I/O tasks to handle the I/O request, and age family portion of the device registry, and notifies the that task is used via synchronous calls by the block storage 45 FinderTM that volumes are available. These volumes then and SCSI families to complete their part in I/O transaction appear on the user's desktop. processing. Whereas, many alterations and modifications of the The Device Registry of the Present Invention present invention will no doubt become apparent to a person The device registry of the present invention comprises an of ordinary skill in the art after having read the foregoing operating system naming service that stores system infor- 50 description, it is to be understood that the particular embodimation. In one embodiment, the device registry is responment shown and described by way of illustration are in no sible for driver replacement and overloading capability so way to be considered limiting. Therefore, reference to the that drivers may be updated, as well as for supporting details of the various embodiments are not intended to limit dynamic driver loading and unloading. the scope of the claims which themselves recite only those In one embodiment, the device registry of the present 55 features regarded as essential to the invention. invention is a tree-structured collection of entries, each of Thus, a method and apparatus for handling I/O requests in which can contain an arbitrary number of name-value pairs a computer system has been described. called properties. Family experts examine the device regisWe claim: try to locate devices or plug-ins available to the family. 1. A computer system comprising: Low-level experts, discussed below, describe platform harda bus; ware by populating the device registry with device nodes for 60 at least one memory coupled to the bus for storing data insertion of devices that will be available for use by appliand programming instructions that include applications cations. and an operating system; and In one embodiment, the device registry contains a device a processing unit coupled to the bus and running the subtree pertinent to the I/O architecture of the present operating system and applications by executing proinvention. The device tree describes the configuration and 65 gramming instructions, wherein an application has a connectivity of the hardware in the system. Each entry in the first plurality of tailored distinct programming interdevice tree has properties that describe the hardware repre- 5,915,131 15 16 faces available to access a plurality of separate sets of 10. The computer system defined in claim 9 wherein the first programming interface is responsive to request from computer system services provided through the operapplications and from other program structures. ating system of the computer system via service 11. The computer system defined in claim 9 wherein the requests. 2. The computer system defined in claim 3 wherein each 5 first programming interface comprises at least one library for converting functions into messages. of the first plurality of tailored distinct programming inter12. The computer system defined in claim 9 wherein the faces are tailored to a type of I/O service provided by each first server receives a message corresponding a service set of I/O services. request from the first programming interface, maps the 3. A computer system comprising: 10 message into a function called by the client, and then calls a bus; the function. at least one memory coupled to the bus for storing data 13. The computer system defined in claim 9 wherein the and programming instructions that include applications message comprises a kernel message. and an operating system, wherein the operating system 14. A computer system comprising: comprises a plurality of servers, and each of the first a bus; plurality of programming interfaces transfer service 15 at least one memory coupled to the bus for storing data requests to one of the plurality of servers, wherein each and programming instructions that comprise applicaof the plurality of servers responds to service requests tions and an operating system; from clients of the separate sets of I/O services; and a processing unit coupled to the bus and running the operating system and applications by executing proa processing unit coupled to the bus and running the operating system and applications by executing pro- 20 gramming instructions, wherein the operation system provides input/output (I/O) services through a tailored graming instructions, wherein an application has a first distinct one of plurality of program structures, each plurality of tailored distinct programming interfaces available to access a plurality of separate sets of I/O tailored distinct program structure comprising: a first programming interface for receiving service services provided through the operating system via 25 service requests. requests for a set of I/O services of a first type, 4. The computer system defined in claim 3 wherein a first server coupled to receive service requests and to service requests are transferred as messages in a messaging dispatch service requests to the I/O services, system. an activation model to define operating environment in 5. The computer system defined in claim 4 wherein each which a service request is to be serviced by the set of of the plurality of servers supports a message port. 30 I/O services, and 6. The computer system defined in claim 3 wherein at at least one specific instance of the set of I/O services least one of the plurality of servers is responsive to service that operate within the activation model, wherein one requests from applications and from at least one other set of of the said at least one specific instances comprises I/O services. a service that accesses another program structure, 7. The computer system defined in claim 3 wherein the 35 and further wherein said one of said at least one operating system further comprises a plurality of activation specific instances communicates to said another promodels, wherein each of the plurality of activation models is gram structure of a second type using a message associated with one of the plurality of servers to provide a created using a library sent to the server of said runtime environment for the set of I/O services to which another program structure. access is provided by said one of the plurality of servers. 15. The computer system defined in claim 9 wherein two 8. The computer system defined in claim 7 wherein at 40 or more I/O services share code or data. least one instance of a service is called by one of the plurality 16. The computer system defined in claim 15 wherein said of servers for execution in an environment set forth by one two or more I/O services are different types. of the plurality of activation models. 17. The computer system defined in claim 9 wherein the 9. A computer system comprising: 45 program structure further comprises a storage mechanism to a bus; maintain identification of available services to which access at least one memory coupled to the bus for storing data is provided via the first server. and programming instructions that comprise applica18. A computer implemented method of accessing I/O tions and an operating system; services of a first type, said computer implemented method a processing unit coupled to the bus and running the comprising the steps of: operating system and applications by executing pro- 50 generating a service request for a first type of I/O services; gramming instructions, wherein the operating system a tailored distinct family server, operating in an operating provides computer system services through a tailored system environment and dedicated to providing access distinct one of a plurality of program structures, each to service requests for the first type of I/O service, tailored distinct program structure comprising: receiving and responding to the service request based a first programming interface for receiving service 55 on an activation model specific to the first type of I/O requests for a set of computer system I/O services of services; and a first type, a processor running an instance of the first type of I/O a first server coupled to receive service requests and to services that is interfaces to the file server to satisfy the dispatch service requests to the computer system I/O service request. 60 services, 19. The method defined in claim 18 wherein the service an activation model to define an operating environment request is generated by an application. in which a service request is to be serviced by the set 20. The method defined in claim 18 wherein the service of computer system I/O services, and request is generated by an instance of an I/O service running at least one specific instance of the set of computer in the operating system environment. system I/O services that operate within the activation 65 model. * * * * * UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO.5, 915,131 DATED June 22, 1999 INVENTOR(S) : Knight, et ale It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below: In column 15 at line 14 delete ''the'' and insert -- a __ In column 15 at line 54 delete ":" and insert -- ; -In column 16 at line 20 delete "operation" and insert -- operating -In column 16 at line 58 delete "interfaces" and insert -- interfaced -- Signed and Sealed this Eighteenth Day of January, 2000 Attest: ~~ Q. TODD DICKINSON Attesting Officer Commissioner of Patents and Trademarks

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