PATENT DOCUMENT

Abstract:
A network of microcontrollers for monitoring and diagnosing the environmental conditions of a computer is disclosed. The network of microcontrollers provides a management system by which computer users can accurately gauge the health of their computer. The network of microcontrollers provides users the ability to detect system fan speeds, internal temperatures and voltage levels. The invention is designed to not only be resilient to faults, but also allows for the system maintenance, modification, and growth—without downtime. Additionally, the present invention allows users to replace failed components, and add new functionality, such as new network interfaces, disk interface cards and storage, without impacting existing users. One of the primary roles of the present invention is to manage the environment without outside involvement. This self-management allows the system to continue to operate even though components have failed.

Full Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 11/586,282, filed on Oct. 25, 2006, which is a divisional of U.S. application Ser. No. 10/675,917, filed on Sep. 29, 2003, now U.S. Pat. No. 7,552,364, issued on Jun. 23, 2009, which is a continuation of U.S. application Ser. No. 09/911,884, filed on Jul. 23, 2001, now U.S. Pat. No. 6,681,342, issued on Jan. 20, 2004, which is a continuation of U.S. application Ser. No. 08/942,402, filed on Oct. 1, 1997, now U.S. Pat. No. 6,338,150, issued on Jan. 8, 2002, which in turn claims priority to the following provisional patent applications, the entirety of which are hereby incorporated herein by reference: 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Title 
                 Appl. No. 
                 Filing Date 
               
               
                   
                   
               
             
             
               
                   
                 “Remote Access and Control of  
                 60/046,397 
                 May 13, 1997 
               
               
                   
                 Environmental Management  
                   
                   
               
               
                   
                 System” 
                   
                   
               
               
                   
                 “Hardware and Software  
                 60/047,016 
                 May 13, 1997 
               
               
                   
                 Architecture for Inter- 
                   
                   
               
               
                   
                 Connecting an  
                   
                   
               
               
                   
                 Environmental Management 
                   
                   
               
               
                   
                 System with a Remote Interface” 
                   
                   
               
               
                   
                 “Self Management Protocol for  
                 60/046,416 
                 May 13, 1997 
               
               
                   
                 a Fly-By-Wire 
                   
                   
               
               
                   
                 Service Processor” 
                   
                   
               
               
                   
                 “Computer System Hardware  
                 60/046,398 
                 May 13, 1997 
               
               
                   
                 Infrastructure for Hot Plugging 
                   
                   
               
               
                   
                 Single and Multi-Function PC 
                   
                   
               
               
                   
                 Cards Without Embedded Bridges” 
                   
                   
               
               
                   
                 “Computer System Hardware  
                 60/046,312 
                 May 13, 1997 
               
               
                   
                 Infrastructure for Hot Plugging 
                   
                   
               
               
                   
                 Multi-Function PCI Cards with 
                   
                   
               
               
                   
                 Embedded Bridges” 
               
               
                   
                   
               
             
          
         
       
     
         [0002]    This application is related to U.S. Pat. No. 6,249,885, entitled, “METHOD FOR MANAGING A DISTRIBUTED PROCESSOR SYSTEM”, Attorney Docket No. MTIPAT.119A; U.S. Pat. No. 6,122,758, entitled “SYSTEM FOR MAPPING ENVIRONMENTAL RESOURCES TO MEMORY FOR PROGRAM ACCESS”, Attorney Docket No. MTIPAT.120A; and U.S. Pat. No. 6,199,173, entitled “METHOD FOR MAPPING ENVIRONMENTAL RESOURCES TO MEMORY FOR PROGRAM ACCESS”, Attorney Docket No. MTIPTAT.121A, and each contains related subject matter and are each incorporated by reference in their entirety. 
     
    
     APPENDICES 
       [0003]    Appendix A, which forms a part of this disclosure, is a list of commonly owned copending U.S. patent applications. Each one of the applications listed in Appendix A is hereby incorporated herein in its entirety by reference thereto. 
         [0004]    Appendix B, which forms part of this disclosure, is a copy of the U.S. provisional patent application filed May 13, 1997, entitled “SELF MANAGEMENT PROTOCOL FOR A FLY-BY-WIRE SERVICE PROCESSOR” and assigned Application No. 60/046,416. Page 1, line 7 of the provisional application has been changed from the original to positively recite that the entire provisional application, including the attached documents, forms part of this disclosure. 
         [0005]    Appendix C, which forms part of this disclosure, is a copy of the U.S. provisional patent application filed May 13, 1997, entitled “HARDWARE AND SOFTWARE ARCHITECTURE FOR INTER-CONNECTING AN ENVIRONMENTAL MANAGEMENT SYSTEM WITH A REMOTE INTERFACE” and assigned Application No. 60/047,016. In view of common pages between the foregoing two applications, a copy of only the first three pages of U.S. provisional patent Application No. 60/047,016 are attached hereto. Page 1, line 7 of the provisional application has been changed from the original to positively recite that the entire provisional application, including the attached documents, forms part of this disclosure. 
       Copyright Rights 
       [0006]    A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. 
       BACKGROUND OF THE INVENTION 
       [0007]    1. Field of the Invention 
         [0008]    The invention relates to the field of fault tolerant computer systems. More particularly, the invention relates to a managing and diagnostic system for evaluating and controlling the environmental conditions of a fault tolerant computer system. 
         [0009]    2. Description of the Related Technology 
         [0010]    As enterprise-class servers become more powerful and more capable, they are also becoming ever more sophisticated and complex. For many companies, these changes lead to concerns over server reliability and manageability, particularly in light of the increasingly critical role of server-based applications. While in the past many systems administrators were comfortable with all of the various components that made up a standards-based network server, today&#39;s generation of servers can appear as an incomprehensible, unmanageable black box. Without visibility into the underlying behavior of the system, the administrator must “fly blind.” Too often, the only indicators the network manager has on the relative health of a particular server is whether or not it is running. 
         [0011]    It is well-acknowledged that there is a lack of reliability and availability of most standards-based servers. Server downtime, resulting either from hardware or software faults or from regular maintenance, continues to be a significant problem. By one estimate, the cost of downtime in mission critical environments has risen to an annual total of $4.0 billion for U.S. businesses, with the average downtime event resulting in a $140 thousand loss in the retail industry and a $450 thousand loss in the securities industry. It has been reported that companies lose as much as $250 thousand in employee productivity for every 1% of computer downtime. With emerging Internet, intranet and collaborative applications taking on more essential business roles every day, the cost of network server downtime will continue to spiral upward. Another major cost is of system downtime administrators to diagnose and fix the system. Corporations are looking for systems which do not require real time service upon a system component failure. 
         [0012]    While hardware fault tolerance is an important element of an overall high availability architecture, it is only one piece of the puzzle. Studies show that a significant percentage of network server downtime is caused by transient faults in the I/O subsystem. Transient failures are those which make a server unusable, but which disappear when the server is restarted, leaving no information which points to a failing component. These faults may be due, for example, to the device driver, the adapter card firmware, or hardware which does not properly handle concurrent errors, and often causes servers to crash or hang. The result is hours of downtime per failure, while a system administrator discovers the failure, takes some action and manually reboots the server. In many cases, data volumes on hard disk drives become corrupt and must be repaired when the volume is mounted. A dismount-and-mount cycle may result from the lack of hot pluggability in current standards-based servers. Diagnosing intermittent errors can be a frustrating and time-consuming process. For a system to deliver consistently high availability, it should be resilient to these types of faults. 
         [0013]    Modern fault tolerant systems have the functionality monitor the ambient temperature of a storage device enclosure and the operational status of other components such the cooling fans and power supply. However, a limitation of these server systems is that they do not contain self-managing processes to correct malfunctions. Thus, if a malfunction occurs in a typical server, the one corrective measure taken by the server is to give notification of the error causing event via a computer monitor to the system administrator. If the system error caused the system to stop running, the system administrator might never know the source of the error. Traditional systems are lacking in detail and sophistication when notifying system administrators of system malfunctions. System administrators are in need of a graphical user interface for monitoring the health of a network of servers. Administrators need a simple point-and-click interface to evaluate the health of each server in the network. In addition, existing fault tolerant servers rely upon operating system maintained logs for error recording. These systems are not capable of maintaining information when the operating system is inoperable due to a system malfunction. 
         [0014]    Existing systems also do not have an interface to control the changing or addition of an adapter. Since any user on a network could be using a particular device on the server, system administrators need a software application that will control the flow of communications to a device before, during, and after a hot plug operation on an adapter. 
         [0015]    Also, in the typical fault tolerant computer system, the control logic for the diagnostic system is associated with a particular processor. Thus, if the environmental control processor malfunctioned, then all diagnostic activity on the computer would cease. In traditional systems, there is no monitoring of fans, and no means to make up cooling capacity lost when a fan fails. Some systems provide a processor located on a plug-in PCI card which can monitor some internal systems, and control turning power on and off. If this card fails, obtaining information about the system, and controlling it remotely, is no longer possible. Further, these systems are not able to affect fan speed or cooling capacity. 
         [0016]    Therefore, a need exists for improvements in server management which will result in greater reliability and dependability of operation. Server users are in need of a management system by which the users can accurately gauge the health of their system. Users need a high availability system that should not only be resilient to faults, but should allow for maintenance, modification, and growth—without downtime. System users should be able to replace failed components, and add new functionality, such as new network interfaces, disk interface cards and storage, without impacting existing users. As system demands grow, organizations must frequently expand, or scale, their computing infrastructure, adding new processing power, memory, storage and I/O capacity. With demand for 24-hour access to critical, server-based information resources, planned system downtime for system service or expansion has become unacceptable. 
       SUMMARY OF THE INVENTION 
       [0017]    Embodiments of the inventive monitoring and management system provide system administrators with new levels of client/server system availability and management. It gives system administrators and network managers a comprehensive view into the underlying health of the server—in real time, whether on-site or off-site. In the event of a failure, the invention enables the administrator to learn why the system failed, why the system was unable to boot, and to control certain functions of the server. 
         [0018]    One embodiment of the invention is a computer monitoring and diagnostic system, comprising: a computer; a plurality of sensors capable of sensing conditions of the computer; and a microcontroller network, comprising a plurality of interconnected microcontrollers, connected to the sensors and the computer, wherein the microcontroller network processes requests for conditions from the computer and responsively provides sensed conditions to the computer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is one embodiment of a top-level block diagram showing a fault tolerant computer system of the invention, including mass storage and network connections. 
           [0020]      FIG. 2  is one embodiment of a block diagram showing a first embodiment of a multiple bus configuration connecting I/O adapters and a network of microcontrollers to the clustered CPUs of the fault tolerant computer system shown in  FIG. 1 . 
           [0021]      FIG. 3  is one embodiment of a block diagram showing a second embodiment of a multiple bus configuration connecting canisters containing I/O adapters and a network of microcontrollers to the clustered CPUs of the fault tolerant system shown in  FIG. 1 . 
           [0022]      FIG. 4  is one embodiment of a top-level block diagram illustrating the microcontroller network shown in  FIGS. 2 and 3 . 
           [0023]      FIGS. 5A ,  5 B, and  5 C are detailed block diagrams showing one embodiment of the microcontroller network shown in  FIG. 4  illustrating the signals and values monitored by each microcontroller, and the control signals generated by the microcontrollers. 
           [0024]      FIG. 6  is one embodiment of a flowchart showing the process by which a remote user can access diagnostic and managing services of the microcontroller network shown in  FIGS. 5A ,  5 B, and  5 C. 
           [0025]      FIG. 7  is one embodiment of a block diagram showing the connection of an industry standard architecture (ISA) bus to the microcontroller network shown in  FIGS. 4 ,  5 A,  5 B, and  5 C. 
           [0026]      FIG. 8  is one embodiment of a flowchart showing the master to slave communications of the microcontrollers shown in  FIGS. 4 ,  5 A,  5 B, and  5 C. 
           [0027]      FIG. 9  is one embodiment of a flowchart showing the slave to master communications of the microcontrollers shown in  FIGS. 4 ,  5 A,  5 B, and  5 C. 
           [0028]      FIGS. 10A and 10B  are flowcharts showing one process by which the System Interface, shown in  FIGS. 4 ,  5 A,  5 B, and  5 C, gets commands and relays commands from the ISA bus to the network of microcontrollers. 
           [0029]      FIGS. 11A and 11B  are flowcharts showing one process by which a Chassis microcontroller, shown in  FIGS. 4 ,  5 A,  5 B, and  5 C, manages and diagnoses the power supply to the computer system. 
           [0030]      FIG. 12  is a flowchart showing one process by which the Chassis controller, shown in  FIGS. 4 ,  5 A,  5 B, and  5 C, monitors the addition and removal of a power supply from the fault tolerant computer system. 
           [0031]      FIG. 13  is a flowchart showing one process by which the Chassis controller, shown in  FIGS. 4 ,  5 A,  5 B, and  5 C, monitors temperature. 
           [0032]      FIGS. 14A and 14B  are flowcharts showing one embodiment of the activities undertaken by CPU A controller, shown in  FIGS. 4 ,  5 A,  5 B, and  5 C. 
           [0033]      FIG. 15  is a detailed flowchart showing one process by which the CPU A controller, show in  FIGS. 4 ,  5 A,  5 B, and  5 C, monitors the fan speed for the system board of the computer. 
           [0034]      FIG. 16  is a flowchart showing one process by which activities of the CPU B controller, shown in  FIGS. 4 ,  5 A,  5 B, and  5 C, scans for system faults. 
           [0035]      FIG. 17  is a flowchart showing one process by which activities of a Canister controller, shown in  FIGS. 4 ,  5 A,  5 B, and  5 C, monitors the speed of the canister fan of the fault tolerant computer system. 
           [0036]      FIG. 18  is a flowchart showing one process by which activities of the System Recorder, shown in  FIGS. 4 ,  5 A,  5 B, and  5 C, resets the NVRAM located on the backplane of the fault tolerant computer system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    The following detailed description presents a description of certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways as defined and covered by the claims. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. 
         [0038]      FIG. 1  is one embodiment of a block diagram showing a fault tolerant computer system of the invention. Typically the computer system is one server in a network of servers and communicating with client computers. Such a configuration of computers is often referred to as a client-server architecture. A fault tolerant server is useful for mission critical applications such as the securities business where any computer down time can result in catastrophic financial consequences. A fault tolerant computer will allow for a fault to be isolated and not propagate through the system thus providing complete or minimal disruption to continuing operation. Fault tolerant systems also provide redundant components such as adapters so service can continue even when one component fails. 
         [0039]    The system includes a fault tolerant computer system  100  connecting to external peripheral devices through high speed I/O channels  102  and  104 . The peripheral devices communicate and are connected to the high speed I/O channels  102  and  104  by mass storage buses  106  and  107 . In different embodiments of the invention, the bus system  106 ,  107  could be Peripheral Component Interconnect (PCI), Microchannel, Industrial Standard Architecture (ISA) and Extended ISA (EISA) architectures. In one embodiment of the invention, the buses  106 ,  107  are PCI. Various kinds of peripheral controllers  108 ,  112 ,  116 , and  128 , may be connected to the buses  106  and  107  including mass storage controllers, network adapters and communications adapters. Mass storage controllers attach to data storage devices such as magnetic disk, tape, optical disk, CD-ROM. These data storage devices connect to the mass storage controllers using one of a number of industry standard interconnects, such as small computer storage interface (SCSI), IDE, EIDE, SMD. Peripheral controllers and I/O devices are generally off-the-shelf products. For instance, sample vendors for a magnetic disk controller  108  and magnetic disks  110  include Qlogic, and Quantum (respectively). Each magnetic disk may hold multiple Gigabytes of data. 
         [0040]    A client server computer system typically includes one or more network interface controllers (NICs)  112  and  128 . The network interface controllers  112  and  128  allow digital communication between the fault tolerant computer system  100  and other computers (not shown) such as a network of servers via a connection  130 . For LAN embodiments of the network adapter, the network media used may be, for example, Ethernet (IEEE 802.3), Token Ring (IEEE 802.5), Fiber Distributed Datalink Interface (FDDI) or Asynchronous Transfer Mode (ATM). 
         [0041]    In the computer system  100 , the high speed I/O channels, buses and controllers ( 102 - 128 ) may, for instance, be provided in pairs. In this example, if one of these should fail, another independent channel, bus or controller is available for use until the failed one is repaired. 
         [0042]    In one embodiment of the invention, a remote computer  130  is connected to the fault tolerant computer system  100 . The remote computer  130  provides some control over the fault tolerant computer system  100 , such as requesting system status. 
         [0043]      FIG. 2  shows one embodiment of the bus structure of the fault tolerant computer system  100 . A number ‘n’ of central processing units (CPUs)  200  are connected through a host bus  202  to a memory controller  204 , which allows for access to semiconductor memory by the other system components. In one embodiment of the invention, there are four CPUs  200 , each being an Intel Pentium® Pro microprocessor. A number of bridges  206 ,  208  and  209  connect the host bus to three additional bus systems  212 ,  214 , and  216 . These bridges correspond to high speed I/O channels  102  and  104  shown in  FIG. 1 . The buses  212 ,  214  and  216  correspond to the buses  106  and  107  shown in  FIG. 1 . The bus systems  212 ,  214  and  216 , referred to as PC buses, may be any standards-based bus system such as PCI, ISA, EISA and Microchannel. In one embodiment of the invention, the bus systems  212 ,  214 ,  216  are PCI. In another embodiment of the invention a proprietary bus is used. 
         [0044]    An ISA Bridge  218  is connected to the bus system  212  to support legacy devices such as a keyboard, one or more floppy disk drives and a mouse. A network of microcontrollers  225  is also interfaced to the ISA bus  226  to monitor and diagnose the environmental health of the fault tolerant system. Further discussion of the network will be provided below. 
         [0045]    A bridge  230  and a bridge  232  connects PC buses  214  and  216  with PC buses  234  and  236  to provide expansion slots for peripheral devices or adapters. Separating the devices  238  and  240  on PC buses  234  and  236  reduces the potential that a device or other transient I/O error will bring the entire system down or stop the system administrator from communicating with the system. 
         [0046]      FIG. 3  shows an alternative bus structure embodiment of the fault tolerant computer system  100 . The two PC buses  214  and  216  contain bridges  242 ,  244 ,  246  and  248  to PC bus systems  250 ,  252 ,  254 , and  256 . As with the PC buses  214  and  216 , the PC buses  250 ,  252 ,  254  and  256  can be designed according to any type of bus architecture including PCI, ISA, EISA, and Microchannel. The PC buses  250 ,  252 ,  254 , and  256  are connected, respectively, to a canister  258 ,  260 ,  262  and  264 . The canisters  258 ,  260 ,  262 , and  264  are casings for a detachable bus system and provide multiple slots for adapters. In the illustrated canister, there are four adapter slots. 
         [0047]    Referring now to  FIG. 4 , the present invention for monitoring and diagnosing environmental conditions may be implemented by using a network of microcontrollers  225  located on the fault tolerant computer system  100 . In one embodiment some of the microcontrollers are placed on a system board or motherboard  302  while other microcontrollers are placed on a backplane  304 . Furthermore, in the embodiment of  FIG. 3 , some of the microcontrollers such as Canister controller A  324  may reside on a removable canister. 
         [0048]      FIG. 4  illustrates that the network of microcontrollers  225  is connected to one of the CPUs  200  by an ISA bus  308 . The ISA  308  bus interfaces the network of microcontrollers  225  which are connected on the microcontroller bus  310  through a System Interface  312 . In one embodiment of the invention, the microcontrollers communicate through an I 2 C serial bus, also referred to as a microcontroller bus  310 . The document “The I 2 C Bus and How to Use It” (Philips Semiconductor, 1992) is hereby incorporated by reference. The I 2 C bus is a bi-directional two-wire bus and operates at a 400 kbps rate in the present embodiment. However, other bus structures and protocols could be employed in connection with this invention. In other embodiments, IEEE 1394 (Firewire), IEEE 422, IEEE 488 (GPIB), RS-185, Apple ADB, Universal Serial Bus (USB), or Controller Area Network (CAN) could be utilized as the microcontroller bus. Control on the microcontroller bus is distributed. Each microcontroller can be a sender (a master) or a receiver (a slave) and each is interconnected by this bus. A microcontroller directly controls its own resources, and indirectly controls resources of other microcontrollers on the bus. 
         [0049]    Here are some of the features of the I 2 C-bus:
       Only two bus line are required: a serial data line (SDA) and a serial clock line (SCL).   Each device connected to the bus is software addressable by a unique address and simple master/slave relationships exist at all times; masters can operate as master-transmitters or as master-receivers.   The bus is a true multi-master bus including collision detection and arbitration to prevent data corruption if two or more masters simultaneously initiate data transfer.   Serial, 8-bit oriented, bi-directional data transfers can be made at up to 400 Kbit/second in the fast mode.       
 
         [0054]    Two wires, serial data (SDA) and serial clock (SCL), carry information between the devices connected to the I 2 C bus. Each device is recognized by a unique address and can operate as either a transmitter or receiver, depending on the function of the device. Further, each device can operate from time to time as both a transmitter and a receiver. For example, a memory device connected to the I 2  C bus could both receive and transmit data. In addition to transmitters and receivers, devices can also be considered as masters or slaves when performing data transfers (see Table 1). A master is the device which initiates a data transfer on the bus and generates the clock signals to permit that transfer. At that time, any device addressed is considered a slave. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Definition of I 2 C-bus terminology 
               
             
          
           
               
                 Term 
                 Description 
               
               
                   
               
               
                 Transmitter 
                 The device which sends the data to the bus 
               
               
                 Receiver 
                 The device which receives the data from the bus 
               
               
                 Master 
                 The device which initiates a transfer, generates  
               
               
                   
                 clock signals and terminates a transfer 
               
               
                 Slave 
                 The device addressed by a master 
               
               
                 Multi-master 
                 More than one master can attempt to control the  
               
               
                   
                 bus at the same time without corrupting the message.  
               
               
                   
                 Each device at separate times may act as a master. 
               
               
                 Arbitration 
                 Procedure to ensure that, if more than one master 
               
               
                   
                 simultaneously tries to control the bus, only one is  
               
               
                   
                 allowed to do so and the message is not corrupted 
               
               
                 Synchronization 
                 Procedure to synchronize the clock signal of  
               
               
                   
                 two or more devices 
               
               
                   
               
             
          
         
       
     
         [0055]    The I 2 C-bus is a multi-master bus. This means that more than one device capable of controlling the bus can be connected to it. As masters are usually microcontrollers, consider the case of a data transfer between two microcontrollers connected to the I 2 C-bus. This highlights the master-slave and receiver-transmitter relationships to be found on the I 2 C-bus. It should be noted that these relationships are not permanent, but only depend on the direction of data transfer at that time. The transfer of data between microcontrollers is further described in  FIG. 8 . 
         [0056]    The possibility of connecting more than one microcontroller to the I 2 C-bus means that more than one master could try to initiate a data transfer at the same time. To avoid the conflict that might ensue from such an event, an arbitration procedure has been developed. This procedure relies on the wired-AND connection of all I 2 C interfaces to the I 2 C-bus. 
         [0057]    If two or more masters try to put information onto the bus, as long as they put the same information onto the bus, there is no problem. Each monitors the state of the SDL. If a microcontroller expects to find that the SDL is high, but finds that it is low, the microcontroller assumes it lost the arbitration and stops sending data. The clock signals during arbitration are a synchronized combination of the clocks generated by the masters using the wired-AND connection to the SCL line. 
         [0058]    Generation of clock signal on the I 2 C-bus is always the responsibility of master devices. Each master microcontroller generates its own clock signals when transferring data on the bus. 
         [0059]    In one embodiment, the command, diagnostic, monitoring and history functions of the microcontroller network  102  are accessed using a global network memory and a protocol has been defined so that applications can access system resources without intimate knowledge of the underlying network of microcontrollers. That is, any function may be queried simply by generating a network “read” request targeted at the function&#39;s known global network address. In the same fashion, a function may be exercised simply by “writing” to its global network address. Any microcontroller may initiate read/write activity by sending a message on the I 2 C bus to the microcontroller responsible for the function (which can be determined from the known global address of the function). The network memory model includes typing information as part of the memory addressing information. 
         [0060]    Referring to  FIG. 4 , in one embodiment of the invention, the network of microcontrollers  310  includes ten processors. One of the purposes of the microcontroller network  225  is to transfer messages to the other components of the server system  100 . The processors or microcontrollers include: a System Interface  312 , a CPU A controller  314 , a CPU B controller  316 , a System Recorder  320 , a Chassis controller  318 , a Canister A controller  324 , a Canister B controller  326 , a Canister C controller  328 , a Canister D controller  330  and a Remote Interface controller  332 . The System Interface controller  312 , the CPU A controller  314  and the CPU B controller  316  are located on a system board  302  in the fault tolerant computer system  100 . Also located on the system board are one or more central processing units (CPUs) or microprocessors  164  and the Industry Standard Architecture (ISA) bus  296  that connects to the System Interface Controller  312 . The CPUs  200  may be any conventional general purpose single-chip or multi-chip microprocessor such as a Pentium7, Pentium® Pro or Pentium® II processor available from Intel Corporation, A MIPS® processor available from Silicon Graphics, Inc., a SPARC processor from Sun Microsystems, Inc., a Power PC® processor available from Motorola, or an ALPHA® processor available from Digital Equipment Corporation. In addition, the CPUs  200  may be any conventional special purpose microprocessor such as a digital signal processor or a graphics processor. 
         [0061]    The System Recorder  320  and Chassis controller  318 , along with a data string such as a random access non-volatile access memory (NVRAM)  322  that connects to the System Recorder  320 , are located on a backplane  304  of the fault tolerant computer system  100 . The data storage  322  may be independently powered and may retain its contents when power is unavailable. The data storage  322  is used to log system status, so that when a failure of the computer  100  occurs, maintenance personnel can access the storage  322  and search for information about what component failed. An NVRAM is used for the data storage  322  in one embodiment but other embodiments may use other types and sizes of storage devices. 
         [0062]    The System Recorder  320  and Chassis controller  318  are the first microcontrollers to power up when server power is applied. The System Recorder  320 , the Chassis controller  318  and the Remote Interface microcontroller  332  are the three microcontrollers that have an independent bias 5 Volt power supplied to them if main server power is off. This independent bias 5 Volt power is provided by a Remote Interface Board (not shown). The Canister controllers  324 - 330  are not considered to be part of the backplane  304  because each is mounted on a card attached to the canister. 
         [0063]      FIGS. 5A ,  5 B, and  5 C are one embodiment of a block diagram that illustrates some of the signal lines that are used by the different microcontrollers. Some of the signal lines connect to actuators and other signal lines connect to sensors. In one embodiment of the invention the microcontrollers in the network are commercially available microcontrollers. Examples of off-the-shelf microcontrollers are the PIC16c65 and the PIC16c74 available from Microchip Technology Inc, the 8051 from Intel Corporation, the 8751 available from Atmel, and a P80CL580 microprocessor available from Philips, could be utilized. 
         [0064]    The Chassis controller  318  is connected to a set of temperature detectors  502 ,  504 , and  506  which read the temperature on the backplane  304  and the system board  302 .  FIG. 5  also illustrates the signal lines that connect the System Recorder  320  to the NVRAM  322  and a timer chip  520 . In one embodiment of the invention, the System Recorder  320  is the only microcontroller that can access the NVRAM  322 . The Canister controller  324  is connected to a Fan Tachometer Signal Mux  508  which is used to detect the speed of the fans. The CPU A controller  314  also is connected to a fan mux  508  which gathers the fan speed of system fans. The CPU A controller  314  displays errors to a user by writing to an LCD display  512 . Any microcontroller can request the CPU A controller  314  to write a message to the LCD display  512 . The System Interface  312  is connected to a response buffer  514  which queues outgoing response signals in the order that they are received. Similarly, a request signal buffer  516  is connected to the System Interface  312  and stores, or queues request signals in the order that they are received. 
         [0065]    Software applications can access the network of microcontrollers  225  by using the software program header file that is listed at the end of the specification in the section titled “Header File for Global Memory Addresses”. This header file provides a global memory address for each function of the microcontroller network  225 . By using the definitions provided by this header file, applications can request and send information to the microcontroller network  225  without needing to know where a particular sensor or activator resides in the microcontroller network. 
         [0066]      FIG. 6  is one embodiment of a flowchart illustrating the process by which under one implementation of the present invention, a remote application connected, say, through the connection of  FIG. 1 , can access the network of microcontrollers  225 . Starting at state  600 , a remote software application, such as a generic system management application like Hewlett-Packard Open View, or an application specific to this computer system, retrieves a management information block (MIB) object by reading and interpreting a MIB file, or by an application&#39;s implicit knowledge of the MIB object&#39;s structure. This retrieval could be the result of an operator using a graphical user interface (GUI), or as the result of some automatic system management process. The MIB is a description of objects, which have a standard structure, and contain information specific to the MIB object ID associated with a particular MIB object. At a block  602 , the remote application builds a request for information by creating a request which references a particular MIB object by its object ID, sends the request to the target computer using a protocol called SNMP (simple network management protocol). SNMP is a type of TCP/IP protocol. Moving to state  604 , the remote software sends the SNMP packet to a local agent Microsoft WinSNMP, for example, which is running on the fault tolerant computer system  100 , which includes the network of microcontrollers  225  ( FIG. 4 ). The agent is a specialized program which can interpret MIB object Ids and objects. The local agent software runs on one of the CPUs  200  of  FIGS. 2 and 3 . 
         [0067]    The local agent examines the SNMP request packet (state  606 ). If the local agent does not recognize the request, the local agent passes the SNMP packet to an extension SNMP agent. Proceeding to state  608 , the extension SNMP agent dissects the object ID. The extension SNMP agent is coded to recognize from the object ID, which memory mapped resources managed by the network of microcontrollers need to be accessed (state  608 ). The agent then builds the required requests for the memory mapped information in the command protocol format understood by the network of microcontrollers  225 . The agent then forwards the request to a microcontroller network device driver (state  610 ). 
         [0068]    The device driver then sends the information to the network of microcontrollers  225  at state  612 . The network of microcontrollers  225  provides a result to the device driver in state  614 . The result is returned to the extension agent, which uses the information to build the MIB object, and return it to the extension SNMP agent (state  616 ). The local SNMP agent forwards the MIB object via SNMP to the remote agent (state  616 ). Finally, in state  620 , the remote agent forwards the result to the remote application software. 
         [0069]    For example, if a remote application needs to know the speed of a fan, the remote application reads a file to find the object ID for fan speed. The object ID for the fan speed request may be “837.2.3.6.2”. Each set of numbers in the object ID represent hierarchical groups of data. For example the number “3” of the object ID represents the cooling system. The “3.6” portion of the object ID represents the fans in the cooling. All three numbers “3.6.2” indicate speed for a particular fan in a particular cooling group. 
         [0070]    In this example, the remote application creates a SNMP packet containing the object ID to get the fan speed on the computer  100 . The remote application then sends the SNMP packet to the local agent. Since the local agent does not recognize the fan speed object ID, the local agent forwards the SNMP packet to the extension agent. The extension agent parses the object ID to identify which specific memory mapped resources of the network of microcontrollers  225  are needed to build the MIB object whose object ID was just parsed. The extension agent then creates a message in the command protocol required by the network of microcontrollers  225 . A device driver which knows how to communicate requests to the network of microcontrollers  225  takes this message and relays the command to the network of microcontrollers  225 . Once the network of microcontrollers  225  finds the fan speed, it relays the results to the device driver. The device driver passes the information to the extension agent. The agent takes the information supplied by the microcontroller network device driver and creates a new SNMP packet. The local agent forwards this packet to the remote agent, which then relays the fan speed which is contained in the packet to the remote application program. 
         [0071]      FIG. 7  is one embodiment of a block diagram of the interface between the network of microcontrollers  225  and the ISA bus  308  of  FIGS. 2 and 3 . The interface to the network of microcontrollers  225  includes a System Interface processor  312  which receives event and request signals, processes these signals, and transmits command, status and response signals to the operating system of the CPUs  200 . In one embodiment, the System Interface processor  312  is a PIC16C65 controller chip, available from Microchip, Technology Inc., which includes an event memory (not shown) organized as a bit vector, having at least sixteen bits. Each bit in the bit vector represents a particular type of event. Writing an event to the System Interface processor  312  sets a bit in the bit vector that represents the event. Upon receiving an event signal from another microcontroller, the System Interface  312  interrupts CPUs  200 . Upon receiving the interrupt, the CPUs  200  will check the status of the System Interface  312  to ascertain that an event is pending. Alternatively, the CPUs  200  may periodically poll the status of the System Interface  312  to ascertain whether an event is pending. The CPUs  200  may then read the bit vector in the System Interface  312  to ascertain the type of event that occurred and thereafter notify a system operator of the event by displaying an event message on a monitor connected to the fault tolerant computer  100  or another computer in the server network. After the system operator has been notified of the event, as described above, she may then obtain further information about the system failure which generated the event signal by accessing the NVRAM  322 . 
         [0072]    The System Interface  312  communicates with the CPUs  200  by receiving request signals from the CPUs  200  and sending response signals back to the CPUs  200 . Furthermore, the System Interface  312  can send and receive status and command signals to and from the CPUs  200 . For example, a request signal may be sent from a software application inquiring as to whether the System Interface  312  has received any event signals, or inquiring as to the status of a particular processor, subsystem, operating parameter. The following discussion explains how in further detail at the state  612 , the device driver sends the request to the network on microcontrollers, and then, how the network on microcontrollers returns the result (state  614 ). A request signal buffer  516  is connected to the System Interface  312  and stores, or queues, request signals in the order that they are received, first in-first out (FIFO). Similarly, a response buffer  514  is connected to the System Interface  312  and queues outgoing response signals in the order that they are received (FIFO). These queues are one byte wide, (messages on the I 2 C bus are sequences of 8-bit bytes, transmitted bit serially on the SDL). 
         [0073]    A message data register (MDR)  707  is connected to the request and response buffers  516  and  514  and controls the arbitration of messages to and from the System Interface  312  via the request and response buffers  516  and  514 . In one embodiment, the MDR  707  is eight bits wide and has a fixed address which may be accessed by the server&#39;s operating system via the ISA bus  226  connected to the MDR  707 . As shown in  FIG. 7 , the MDR  707  has an I/O address of OCC0 h. When software application running on one of the CPUs  200  desires to send a request signal to the System Interface  312 , it does so by writing a message one byte at a time to the MDR  707 . The application then indicates to the system interface processor  312  that the command has been completely written, and may be processed. 
         [0074]    The system interface processor  312  writes the response one byte at a time to the response queue, then indicates to the CPU (via an interrupt or a bit in the status register) that the response is complete, and ready to be read. The CPU  200  then reads the response queue one byte at a time by reading the MDR  707  until all bytes of the response are read. 
         [0075]    The following is one embodiment of the command protocol used to communicate with the network of microcontrollers  225 . 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Command Protocol Format 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 READ REQUEST FORMAT 
                 WRITE REQUEST FORMAT 
               
               
                   
               
             
          
           
               
                 Offset 
                   
                   
                 Offset 
                   
                   
               
               
                 Byte 0 
                 Slave Add 
                 0 
                 Byte 0 
                 Slave Add 
                 0 
               
               
                   
                 (7 bits) 
                 LSBit 
                   
                 (7 bits) 
                 LSBit 
               
               
                 Byte 1 
                 MSBit (1) 
                 Type 
                 Byte 1 
                 MSBit (0) 
                 Type 
               
             
          
           
               
                 Byte 2 
                 Command ID (LSB) 
                 Byte 2 
                 Command ID (LSB) 
               
               
                 Byte 3 
                 Command ID (MSB) 
                 Byte 3 
                 Command ID (MSB) 
               
               
                 Byte 4 
                 Read Request Length ( 
                 Byte 4 
                 Write Request Length (I 
               
               
                 Byte 5 
                 Check Sum 
                 Byte 5 
                 Data Byte 1 
               
               
                   
                   
                 : 
                 : 
               
             
          
           
               
                   
                 Byte N + 4 
                 Data Byte N 
               
             
          
           
               
                   
                   
                   
                 Byte N + 5 
                 Check Sum 
               
               
                   
               
             
          
           
               
                 READ RESPONSE FORMAT 
                 WRITE RESPONSE FORMAT 
               
               
                   
               
             
          
           
               
                 Offset 
                   
                 Offset 
                   
               
             
          
           
               
                 Byte 0 
                 Slave Add 
                 1 
                 Byte 0 
                 Slave Add 
                 1 
               
               
                   
                   
                 (7 bits) 
                 LSBit 
                 (7 bits) 
                 LSBit 
               
             
          
           
               
                 Byte 1 
                 Read Response Lengt 
                 Byte 1 
                 Write 
                   
               
               
                   
                 (N) 
                   
                 Response 
                   
               
               
                 Byte 2 
                 Data Byte 1 
                   
                 Length (0) 
                   
               
               
                 : 
                 : 
                 Byte 2 
                 Status 
                   
               
               
                 Byte N + 1 
                 Data Byte N 
                 Byte 3 
                 Check Sum 
                   
               
               
                 Byte N + 2 
                 Status 
                 Byte 4 
                 Inverted Slave Addr 
                   
               
             
          
           
               
                 Byte N + 3 
                 Check Sum 
                   
               
               
                 Byte N + 4 
                 Inverted Slave Addr 
               
               
                   
               
             
          
         
       
     
         [0076]    The following is a description of each of the fields in the command protocol. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Description of Command Protocol Fields 
               
             
          
           
               
                 FIELD 
                 DESCRIPTION 
               
               
                   
               
               
                 Slave Addr 
                 Specifies the processor identification code.  
               
               
                   
                 This field is 7 bits 
               
               
                   
                 wide. Bit [7 . . . 1].  
               
               
                 LSBit 
                 Specifies what type of activity is taking place.  
               
               
                   
                 If LSBit is clear 
               
               
                   
                 (0), the master is writing to a slave. If LSBit  
               
               
                   
                 is set (1), the 
               
               
                   
                 master is reading from a slave. 
               
               
                 MSBit 
                 Specifies the type of command. It is bit 7  
               
               
                   
                 of byte 1 of a request. If this bit is clear (0),  
               
               
                   
                 this is a write command. If it is 
               
               
                   
                 set (1), this is a read command. 
               
               
                 Type 
                 Specifies the data type of this command,  
               
               
                   
                 such as bit or string. 
               
               
                 Command ID (LSB) 
                 Specifies the least significant byte of the  
               
               
                   
                 address of the processor. 
               
               
                 Command ID (MSB) 
                 Specifies the most significant byte of the  
               
               
                   
                 address of the processor. 
               
               
                 Length (N) 
                   
               
               
                 Read Request 
                 Specifies the length of the data that the master  
               
               
                   
                 expects to get back from a read response. 
               
               
                   
                 The length, which is in bytes, 
               
               
                   
                 does not include the Status, Check  
               
               
                   
                 Sum, and Inverted Slave 
               
               
                   
                 Addr fields. 
               
               
                 Read Response 
                 Specifies the length of the data immediately  
               
               
                   
                 following this byte, that is byte 2  
               
               
                   
                 through byte N+1. 
               
               
                   
                 The length, which is in bytes, does not include  
               
               
                   
                 the Status, Check Sum, and Inverted Slave 
               
               
                   
                 Addr fields. 
               
               
                 Write Request 
                 Specifies the length of the data immediately  
               
               
                   
                 following this byte, that is  
               
               
                   
                 byte 2 through byte N+1. 
               
               
                   
                 The length, which is in bytes, does  
               
               
                   
                 not include the 
               
               
                   
                 Status, Check Sum, and Inverted Slave 
               
               
                   
                 Addr fields. 
               
               
                 Write Response 
                 Always specified as 0. 
               
               
                 Data Byte 1 
                 Specifies the data in a read request  
               
               
                   
                 and response, and a write 
               
               
                   
                 request. 
               
               
                 Data Byte N 
                   
               
               
                 Status 
                 Specifies whether or not this command  
               
               
                   
                 executes successfully. 
               
               
                   
                 A non-zero entry indicates a failure. 
               
               
                 Check Sum 
                 Specifies a direction control byte to ensure  
               
               
                   
                 the integrity of a 
               
               
                   
                 message on the wire. 
               
               
                 Inverted Slave Addr 
                 Specifies the Slave Addr, which is inverted. 
               
               
                   
               
             
          
         
       
     
         [0077]    The System Interface  312  further includes a command and status register (CSR)  709  which initiates operations and reports on status. The operation and functionality of CSR  709  is described in further detail below. Both synchronous and asynchronous I/O modes are provided by the System Interface  312 . During a synchronous mode of operation, the device driver waits for a request to be completed. During an asynchronous mode of operation the device driver sends the request, and asks to be interrupted when the request completes. To support asynchronous operations, an interrupt line  711  is connected between the System Interface  312  and the ISA bus  226  and provides the ability to request an interrupt when asynchronous I/O is complete, or when an event occurs while the interrupt is enabled. As shown in  FIG. 7 , in one embodiment, the address of the interrupt line  711  is fixed and indicated as IRQ  15  which is an interrupt address number used specifically for the ISA bus  226 . 
         [0078]    The MDR  707  and the request and response buffers  516  and  514 , respectively, transfer messages between a software application running on the CPUs  200  and the failure reporting system of the invention. The buffers  516  and  514  have two functions: (1) they store data in situations where one bus is running faster than the other, i.e., the different clock rates, between the ISA bus  226  and the microcontroller bus  310 ; and (2) they serve as interim buffers for the transfer of messages—this relieves the System Interface  312  of having to provide this buffer. 
         [0079]    When the MDR  707  is written to by the ISA bus  226 , it loads a byte into the request buffer  516 . When the MDR  707  is read from the ISA bus  516 , it unloads a byte from the response buffer  514 . The System Interface  312  reads and executes messages from buffer  516  when a message command is received in the CSR  709 . A response message is written to the response buffer  514  when the System Interface  312  completes executing the command. The system operator receives a completed message over the microcontroller bus  310 . A software application can read and write message data to and from the buffers  516  and  514  by executing read and write instructions through the MDR  707 . 
         [0080]    The CSR  709  has two functions. The first is to initiate commands, and the second is to report status. The System Interface commands are usually executed synchronously. That is, after issuing a command, the microcontroller network device driver should continue to poll the CSR  709  status to confirm command completion. In addition to synchronous I/O mode, the microcontroller network device driver can also request an asynchronous I/O mode for each command by setting a “Asyn Req” bit in the command. In this mode, an interrupt is generated and sent to the ISA bus  226 , via the interrupt line  711 , after the command has completed executing. 
         [0081]    In the described embodiment, the interrupt is asserted through IRQ 15  of the ISA programmable interrupt controller (PIC). The ISA PIC interrupts the CPU  200   s  when a signal transitioning from high to low, or from low to high, is detected at the proper input pin (edge triggered). Alternatively, the interrupt line  711  may utilize connect to a level-triggered input. A level-triggered interrupt request is recognized by keeping the signal at the same level, or changing the level of a signal, to send an interrupt. The microcontroller network device driver can either enable or disable interrupts by sending “Enable Ints” and “Disable Ints” commands to the CSR  701 . If the interrupt  711  line is enabled, the System Interface  312  asserts the interrupt signal IRQ 15  of the PIC to the ISA bus  226 , either when an asynchronous I/O is complete or when an event has been detected. 
         [0082]    In the embodiment shown in  FIG. 2 , the System Interface  312  may be a single-threaded interface. Since messages are first stored in the queue, then retrieved from the queue by the other side of the interface, a device driver should write one message, containing a sequence of bytes, at a time. Thus, only one message should be in progress at a time using the System Interface  312 . Therefore, a program or application must allocate the System Interface  312  for its use before using it, and then de-allocate the interface  514  when its operation is complete. The CSR  709  indicates which operator is allocated access to the System Interface  312 . 
         [0083]    Referring to  FIGS. 2 and 7 , an example of how messages are communicated between the System Interface  312  and CPUs  200  in one embodiment of the invention is as follows (all byte values are provided in hexadecimal numbering). A system management program (not shown) sends a command to the network of microcontrollers  225  to check temperature and fan speed. To read the temperature from CPU A controller  314  the program builds a message for the device driver to forward to the network of microcontrollers  225 . First, the device driver on CPUs  200  allocates the interface by writing the byte “01” to the CSR  709 . If another request was received, the requestor would have to wait until the previous request was completed. To read the temperature from Chassis controller  318  the device driver would write into the request queue  516  through the MDR  707  the bytes “02 83 03 00 FF”. The first byte “02” would signify to the System Interface  312  that a command is intended for the Chassis controller  318 . The first bits of the second byte “83” indicates that a master is writing to a slave. The last or least significant three bits of the byte “83” indicate the data type of the request. The third and fourth bytes “03 00” indicate that the read request temperature function of the Chassis controller  318  is being requested. The final byte “FF” is the checksum. 
         [0084]    After writing the bytes to the MDR  707 , a “13” (message command) is written by the device driver to the CSR  709 , indicating the command is ready to be executed. The System Interface processor  312  passes the message bytes to the microcontroller bus  310 , receives a response, and puts the bytes into the response FIFO  514 . Since there is only one system interface processor  312 , there is no chance that message bytes will get intermingled. 
         [0085]    After all bytes are written to the response FIFO, the System Interface processor  312  sets a bit in the CSR  709  indicating message completion. If directed to do so by the device driver, the system interface  312  asserts an interrupt on IRQ  15  upon completion of the task. 
         [0086]    The CPUs  200  would then read from the response buffer  516  through the MDR  707  the bytes “02 05 27 3C 27 26 27 00”. The first byte in the string is the slave address shown as Byte 0 in the Read Response Format. The first byte 02 indicates that the CPU A Chassis controller  318  was the originator of the message. The second byte “05” indicates the number of temperature readings that follow. The second Byte “05” maps to Byte 1 of the Read Response Format. In this example, the Chassis controller  318  returned five temperatures. The second reading, byte “3C” (60 decimal) is above normal operational values. The last byte “00” is a check sum which is used to ensure the integrity of a message. 
         [0087]    The CPUs  200  agent and device driver requests the fan speed by writing the bytes “03 83 04 00 FF” to the network of microcontroller  225 . Each byte follows the read request format specified in Table 2. The first byte “03” indicates that the command is for the CPU A Controller  314 . The second byte “83” indicates that the command is a read request of a string data type. 
         [0088]    A response of “03 06 41 43 41 42 41 40 00” would be read from MDR  707  by the device driver. The first byte “03” indicates to the device driver that the command is from the CPU A controller  314 . The speed bytes “41 43 41 42 41 40” indicate the revolutions per second of a fan in hexadecimal. The last byte read from the MDR  707  “00” is the checksum. 
         [0089]    Since one of the temperatures is higher than the warning threshold, 55□C, and fan speed is within normal (low) range, a system administrator or system management software may set the fan speed to high with the command bytes “03 01 01 00 01 01 FF”. The command byte “03” indicates that the command is for the CPU A  314 . The first byte indicates that a write command is requested. The third and fourth bytes, which correspond to byte 2 and 3 of the write request format, indicate a request to increase the fan speed. The fifth byte, which corresponds to byte 4 of the write request format indicates to the System Interface  312  that one byte is being sent. The sixth byte contains the data that is being sent. The last byte “FF” is the checksum. 
         [0090]      FIG. 8  is one embodiment of a flowchart describing the process by which a master microcontroller communicates with a slave microcontroller. Messages between microcontrollers can be initiated by any microcontroller on the microcontroller bus  310  ( FIG. 4 ). A master microcontroller starts out in state  800 . 
         [0091]    In state  802 , the microcontroller arbitrates for the start bit. If a microcontroller sees a start bit on the microcontroller bus  310 , it cannot gain control of the microcontroller bus  310 . The master microcontroller proceeds to state  804 . In the state  804 , the microcontroller increments a counter every millisecond. The microcontroller then returns to state  800  to arbitrate again for the start bit. If at state  806  the count reaches 50 ms, the master has failed to gain the bus (states  808  and  810 ). The microcontroller then returns to the state  800  to retry the arbitration process. 
         [0092]    If in the state  802 , no start bit is seen on the microcontroller bus  310 , the microcontroller bus  310  is assumed to be free (i.e., the microcontroller has successfully arbitrated won arbitration for the microcontroller bus  310 ). The microcontroller sends a byte at a time on the microcontroller bus  310  (state  812 ). After the microcontroller has sent each byte, the microcontroller queries the microcontroller bus  310  to insure that the microcontroller bus  310  is still functional. If the SDA and SCL lines of the microcontroller bus  310  are not low, the microcontroller is sure that the microcontroller bus  310  is functional and proceeds to state  816 . If the SDA and SCL lines are not drawn high, then the microcontroller starts to poll the microcontroller bus  310  to see if it is functional. Moving to state  819 , the microcontroller increments a counter Y and waits every 22 microseconds. If the counter Y is less than five milliseconds (state  820 ), the state  814  is reentered and the microcontroller bus  310  is checked again. If the SDA and SCL lines are low for 5 milliseconds (indicated when, at state  820 , the counter Y exceeds 5 milliseconds), the microcontroller enters state  822  and assumes there is a microcontroller bus error. The microcontroller then terminates its control of the microcontroller bus  310  (state  824 ). 
         [0093]    If in the state  814 , the SDA/SCL lines do not stay low (state  816 ), the master microcontroller waits for a response from a slave microcontroller (state  816 ). If the master microcontroller has not received a response, the microcontroller enters state  826 . The microcontroller starts a counter which is incremented every one millisecond. Moving to state  828 , if the counter reaches fifty milliseconds, the microcontroller enters state  830  indicating a microcontroller bus error. The microcontroller then resets the microcontroller bus  310  (state  832 ). 
         [0094]    Returning to state  816 , if the master microcontroller does receive a response in state  816 , the microcontroller enters state  818  and receives the data from the slave microcontroller. At state  820 , the master microcontroller is finished communicating with the slave microcontroller. 
         [0095]      FIG. 9  is one embodiment of a block diagram illustrating the process by which a slave microcontroller communicates with a master microcontroller. Starting in state  900 , the slave microcontroller receives a byte from a master microcontroller. The first byte of an incoming message always contains the slave address. This slave address is checked by all of the microcontrollers on the microcontroller bus  310 . Whichever microcontroller matches the slave address to its own address handles the request. 
         [0096]    At a decision state  902 , an interrupt is generated on the slave microcontroller. The microcontroller checks if the byte received is the first received from the master microcontroller (state  904 ). If the current byte received is the first byte received, the slave microcontroller sets a bus time-out flag (state  906 ). Otherwise, the slave microcontroller proceeds to check if the message is complete (state  908 ). If the message is incomplete, the microcontroller proceeds to the state  900  to receive the remainder of bytes from the master microcontroller. If at state  908 , the slave microcontroller determines that the complete message has been received, the microcontroller proceeds to state  909 . 
         [0097]    Once the microcontroller has received the first byte, the microcontroller will continue to check if there is an interrupt on the microcontroller bus  310 . If no interrupt is posted on the microcontroller bus  310 , the slave microcontroller will check to see if the bus time-out flag is set. The bus time-out flag is set once a byte has been received from a master microcontroller. If in the decision state  910  the microcontroller determines that the bus time-out flag is set, the slave microcontroller will proceed to check for an interrupt every 10 milliseconds up to 500 milliseconds. For this purpose, the slave microcontroller increments the counter every 10 milliseconds (state  912 ). In state  914 , the microcontroller checks to see if the microcontroller bus  310  has timed out. If the slave microcontroller has not received additional bytes from the master microcontroller, the slave microcontroller assumes that the microcontroller bus  310  is hung and resets the microcontroller bus  310  (state  916 ). Next, the slave microcontroller aborts the request and awaits further requests from other master microcontrollers (state  918 ). 
         [0098]    Referring to the state  909 , the bus timeout bit is cleared, and the request is processed and the response is formulated. Moving to state  920 , the response is sent a byte at a time. At state  922 , the same bus check is made as was described for the state  814 . States  922 ,  923  and  928  form the same bus check and timeout as states  814 ,  819  and  820 . If in state  928  this check times out, a bus error exists, and this transaction is aborted (states  930  and  932 ). 
         [0099]      FIGS. 10A and 10B  are flow diagrams showing one process by which the System Interface  312  handles requests from other microcontrollers in the microcontroller network and the ISA bus  226  ( FIGS. 4 and 5 ). The System Interface  312  relays messages from the ISA bus  226  to other microcontrollers in the network of microcontrollers  225 . The System Interface  312  also relays messages from the network of microcontrollers to the ISA bus  226 . 
         [0100]    Referring to  FIGS. 10A and 10B , the System Interface  312  initializes all variables and the stack pointer (state  1000 ). Moving to state  1002 , the System Interface  312  starts its main loop in which it performs various functions. The System Interface  312  next checks the bus timeout bit to see if the microcontroller bus  310  has timed-out (decision state  1004 ). If the microcontroller bus  310  has timed-out, the System Interface  312  resets the microcontroller bus  310  in state  1006 . 
         [0101]    Proceeding to a decision state  1008 , the System Interface  312  checks to see if any event messages have been received. An event occurs when the System Interface  312  receives information from another microcontroller regarding a change to the state of the system. At state  1010 , the System Interface  312  sets the event bit in the CSR  709  to one. The System Interface  312  also sends an interrupt to the operating system if the CSR  709  has requested interrupt notification. 
         [0102]    Proceeding to a decision state  1012 , the System Interface  312  checks to see if a device driver for the operating system has input a command to the CSR. If the System Interface  312  does not find a command, the System Interface  312  returns to state  1002 . If the System Interface does find a command from the operating system, the System Interface parses the command. For the “allocate command”, the System Interface  312  resets the queue to the ISA bus  226  resets the done bit in the CSR  709  (state  1016 ) and sets the CSR Interface Owner ID (state  1016 ). The Owner ID bits identify which device driver owns control of the System Interface  312 . 
         [0103]    For the “de-allocate command”, the System Interface  312  resets the queue to the ISA bus  226 , resets the done bit in the CSR  709 , and clears the Owner ID bits (state  1018 ). 
         [0104]    For the “clear done bit command” the System Interface  312  clears the done bit in the CSR  709  (state  1020 ). For the “enable interrupt command” the System Interface  312  sets the interrupt enable bit in the CSR  709  (state  1022 ). For the “disable interrupt command”, the System Interface  312  sets the interrupt enable bit in the CSR  709  (state  1024 ). For the “clear interrupt request command”, the System Interface  312  clears the interrupt enable bit in the CSR  709  (state  1026 ). 
         [0105]    If the request from the operating system was not meant for the System Interface  312 , the command is intended for another microcontroller in the network  225 . The only valid command remaining is the “message command”. Proceeding to state  1028 , the System Interface  312  reads message bytes from the request buffer  516 . From the state  1028 , the System Interface  312  proceeds to a decision state  1030  in which the System Interface  312  checks whether the command was for itself. If the command was for the System Interface  312 , moving to state  1032 , the System Interface  312  processes the command. If the ID did not match an internal command address, the System Interface  312  relays the command the appropriate microcontroller (state  1034 ) by sending the message bytes out over the microcontroller bus  310 . 
         [0106]      FIGS. 11A and 11B  are flowcharts showing an embodiment of the functions performed by the Chassis controller  318 . Starting in the state  1100 , the Chassis controller  318  initializes its variables and stack pointer. 
         [0107]    Proceeding to state  1102 , the Chassis controller  318  reads the serial numbers of the microcontrollers contained on the system board  302  and the backplane  304 . The Chassis controller  318  also reads the serial numbers for the Canister controllers  324 ,  326 ,  328  and  330 . The Chassis controller  318  stores all of these serial numbers in the NVRAM  322 . 
         [0108]    Next, the Chassis controller  318  start its main loop in which it performs various diagnostics (state  1104 ). The Chassis controller  318  checks to see if the microcontroller bus  310  has timed-out (state  1106 ). If the bus has timed-out, the Chassis controller  318  resets the microcontroller bus  310  (state  1008 ). If the microcontroller bus  310  has not timed out the Chassis controller proceeds to a decision state  1110  in which the Chassis controller  318  checks to see if a user has pressed a power switch. 
         [0109]    If the Chassis controller  318  determines a user has pressed a power switch, the Chassis controller changes the state of the power to either on or off (state  1112 ). Additionally, the Chassis controller logs the new power state into the NVRAM  322 . 
         [0110]    The Chassis controller  318  proceeds to handle any power requests from the Remote Interface  332  (state  1114 ). As shown in  FIG. 9 , a power request message to this microcontroller is received when the arriving message interrupts the microcontroller. The message is processed and a bit is set indicating request has been made to toggle power. At state  1114 , the Chassis controller  318  checks this bit. If the bit is set, the Chassis controller  318  toggles the system, i.e., off-to-on or on-to-off, power and logs a message into the NVRAM  322  that the system power has changed state (state  1116 ). 
         [0111]    Proceeding to state  1118 , the Chassis controller  318  checks the operating system watch dog counter for a time out. If the Chassis controller  318  finds that the operating system has failed to update the timer, the Chassis controller  318  proceeds to log a message with the NVRAM  322  (state  1120 ). Additionally, the Chassis controller  318  sends an event to the System Interface  312  and the Remote Interface  332 . 
         [0112]    Since it takes some time for the power supplies to settle and produce stable DC power, the Chassis controller delays before proceeding to check DC (state  1122 ). 
         [0113]    The Chassis controller  318  then checks for changes in the canisters  258 - 264  (state  1124 ), such as a canister being inserted or removed. If a change is detected, the Chassis controller  318  logs a message to the NVRAM  322  (state  1126 ). Additionally, the Chassis controller  318  sends an event to the System Interface  312  and the Remote Interface  332 . 
         [0114]    The Chassis controller  318  proceeds to check the power supply for a change in status (state  1128 ). The process by which the Chassis controller  318  checks the power supply is described in further detail in the discussion for  FIG. 12 . 
         [0115]    The Chassis controller then checks the temperature of the system (state  1132 ). The process by which the Chassis controller  318  checks the temperature is described in further detail in the discussion for  FIG. 13 . 
         [0116]    At state  1136 , the Chassis controller  318  reads all of the voltage level signals. The Chassis controller  318  saves these voltage levels values in an internal register for reference by other microcontrollers. 
         [0117]    Next, the Chassis controller  318  checks the power supply signals for AC/DC changes (state  1138 ). If the Chassis controller  318  detects a change in the Chassis controller  318 , the Chassis controller  318  logs a message to the NVRAM  322  (state  1140 ). Additionally, the Chassis controller  318  sends an event to the System Interface  312  and the Remote Interface  332  that a AC/DC signal has changed. The Chassis controller  318  then returns to state  1104  to repeat the monitoring process. 
         [0118]      FIG. 12  is a flowchart showing one process by which the Chassis controller  318  checks the state of the redundant power supplies termed number  1  and  2 . These power supplies are monitored and controlled by the chassis controller  318  through the signal lines shown in  FIG. 5A . When a power supply fails or requires maintenance, the other supply maintains power to the computer  100 . To determine whether a power supply is operating properly or not, its status of inserted or removed (by maintenance personnel) should be ascertained. Furthermore, a change in status should be recorded in the NVRAM  322 .  FIG. 12  describes in greater detail the state  1128  shown in  FIG. 11B . 
         [0119]    Starting in state  1202 , the Chassis controller  318  checks the power supply bit. If the power supply bit indicates that a power supply should be present, the Chassis controller checks whether power supply “number  1 ” has been removed (state  1204 ). If power supply number  1  has been removed, the chassis microcontroller  318  checks whether its internal state indicates power supply number one should be present. If the internal state was determined to be present, then the slot is checked to see whether power supply number  1  is still physically present (state  1204 ). If power supply number  1  has been removed, the PS_PRESENT# 1  bit is changed to not present (state  1208 ). The Chassis controller  318  then logs a message in the NVRAM  322 . 
         [0120]    Referring to state  1206 , if the PS_PRESENT# 1  bit indicates that power supply number  1  is not present, the Chassis controller  318  checks whether power supply number  1  has been inserted (i.e., checks to see if it is now physically present) (state  1206 ). If it has been inserted, the Chassis controller  318  then logs a message into the NVRAM  322  that the power supply number  1  has been inserted (state  1210 ) and changes the value of PS_PRESENT# 1  to present. 
         [0121]    After completion, states  1204 ,  1206 ,  1208 , and  1210  proceed to state  1212  to monitor power supply number  2 . The Chassis controller  318  checks whether the PS_PRESENT# 2  bit is set to present. If the PS_PRESENT# 2  bit indicates that power supply “number  2 ” should be there, the Chassis controller  318  proceeds to state  1224 . Otherwise, the Chassis controller  318  proceeds to state  1226 . At state  1224 , the Chassis controller  318  checks if power supply number  2  is still present. If power supply number  2  has been removed, the Chassis controller  318  logs in the NVRAM  322  that power supply number  2  has been removed (state  1228 ). The chassis controller also changes the value of PS_PRESENT# 2  bit to not present. 
         [0122]    Referring to decision state  1226 , if the PS_PRESENT# 2  bit indicates that no power supply number  2  is present, the Chassis controller  318  checks if power supply number  2  has been inserted. If so, the Chassis controller  318  then logs a message into the NVRAM  322  that power supply number  2  has been inserted and changes the value of PS_PRESENT# 2  to present (state  1230 ). After completion of states  1224 ,  1226 ,  1228 , and  1230 , the chassis controller  318  proceeds to state  1232  to monitor the AC/DC power supply changed signal. 
         [0123]    If in decision state  1234  the Chassis controller  318  finds that the AC/DC power supply changed signal from the power supplies is asserted, the change in status is recorded in state  1236 . The Chassis controller  318  continues the monitoring process by proceeding to the state  1132  in  FIG. 11B . 
         [0124]      FIG. 13  is a flowchart showing one process by which the Chassis controller  318  monitors the temperature of the system. As shown in  FIG. 5A , the Chassis controller  318  receives temperature detector signal lines from five temperature detectors located on the backplane and the motherboard. If either component indicates it is overheating, preventative action may be taken manually, by a technician, or automatically by the network of microcontrollers  225 .  FIG. 13  describes in greater detail the state  1132  shown in  FIG. 11B . 
         [0125]    To read the temperature of the Chassis, the Chassis controller  318  reads the temperature detectors  502 ,  504 , and  506  (state  1300 ). In the embodiment of the invention shown in  FIG. 13  there are five temperature detectors (two temperature detectors not shown). Another embodiment includes three temperature detectors as shown. 
         [0126]    The Chassis controller  318  checks the temperature detector  502  to see if the temperature is less than −25□C or if the temperature is greater than or equal to 55□C (state  1308 ). Temperatures in this range are considered normal operating temperatures. Of course, other embodiments may use other temperature ranges. If the temperature is operating inside normal operating boundaries, the Chassis controller  318  proceeds to state  1310 . If the temperature is outside normal operating boundaries, the Chassis controller  318  proceeds to state  1312 . At state  1312 , the Chassis controller  318  evaluates the temperature a second time to check if the temperature is greater than or equal to 70□C or less than or equal to −25□C. If the temperature falls below or above outside of these threshold values, the Chassis controller proceeds to state  1316 . Temperatures in this range are considered so far out of normal operating temperatures, that the computer  100  should be shutdown. Of course, other temperature ranges may be used in other embodiments. 
         [0127]    Referring to state  1316 , if the temperature level reading is critical, the Chassis controller  318  logs a message in the NVRAM  322  that the system was shut down due to excessive temperature. The Chassis controller  318  then proceeds to turn off power to the system in state  1320 , but may continue to operate from a bias or power supply. 
         [0128]    Otherwise, if the temperature is outside normal operating temperatures, but only slightly deviant, the Chassis controller  318  sets a bit in the temperature warning status register (state  1314 ). Additionally, the Chassis controller  318  logs a message in the NVRAM  322  that the temperature is reaching dangerous levels (state  1318 ). 
         [0129]    The Chassis controller  318  follows the aforementioned process for each temperature detector on the system. Referring back to state  1310 , which was entered after determining a normal temperature from one of the temperature detectors, the Chassis controller  318  checks a looping variable “N” to see if all the sensors were read. If all sensors were not read, the Chassis controller  318  returns to state  1300  to read another temperature detector. Otherwise, if all temperature detectors were read, the Chassis controller  318  proceeds to state  1322 . At state  1322 , the Chassis controller  318  checks a warning status register (not shown). If no bit is set in the temperature warning status register, the Chassis controller  318  returns to the state  1136  in  FIG. 11B . If the Chassis controller  318  determines that a bit in the warning status register was set for one of the sensors, the Chassis controller  318  proceeds to recheck all of the sensors (state  1324 ). If the temperature of the sensors are still at a dangerous level, the Chassis Controller  318  maintains the warning bits in the warning status register. The Chassis controller  318  then proceeds to the state  1136  ( FIG. 11B ). At state  1324 , if the temperatures of the sensors are now at normal operating values, the Chassis controller  318  proceeds to clear all of the bits in the warning status register (state  1326 ). After clearing the register, the Chassis controller  318  proceeds to state  1328  to log a message in the NVRAM  322  that the temperature has returned to normal operational values, and the Chassis controller  318  proceeds to the state  11136  ( FIG. 11B ). 
         [0130]      FIGS. 14A and 14B  are flowcharts showing the functions performed by one embodiment of the CPU A controller  314 . The CPU A controller  314  is located on the system board  302  and conducts diagnostic checks for: a microcontroller bus timeout, a manual system board reset, a low system fan speed, a software reset command, general faults, a request to write to flash memory, checks system flag status, and a system fault. 
         [0131]    The CPU A controller  314 , starting in state  1400 , initializes its variables and stack pointer. Next, in state  1402  the CPU A controller  314  starts its main loop in which it performs various diagnostics which are described below. At state  1404 , the CPU A controller  314  checks the microcontroller bus  310  for a time out. If the microcontroller bus  310  has timed out, the CPU A controller  314  resets the microcontroller bus  310  (state  1406 ). From either state  1404  or  1406 , the CPU A controller  314  proceeds to check whether the manual reset switch (not shown) is pressed on the system board  302  (decision state  1408 ). If the CPU A controller  314  determines that the manual reset switch is pressed, the CPU A controller resets system board by asserting a reset signal (state  1410 ). 
         [0132]    From either state  1408  or  1410 , the CPU A controller  314  proceeds to check the fan speed (decision state  1412 ). If any of a number of fans speed is low (see  FIG. 15  and discussion below), the CPU A controller  314  logs a message to NVRAM  322  (state  1414 ). Additionally, the CPU A controller  314  sends an event to the Remote Interface  334  and the System Interface  312 . The CPU A controller  314  next proceeds to check whether a software reset command was issued by either the computer  100  or the remote computer  132  (state  1416 ). If such a command was sent, the CPU A controller  314  logs a message in NVRAM  322  that system software requested the reset command (state  1418 ). Additionally, the CPU A controller  314  also resets the system bus  202 . 
         [0133]    From either state  1416  or  1418 , the CPU A controller  314  checks the flags bits (not shown) to determine if a user defined system fault occurred (state  1420 ). If the CPU A controller  314  determines that a user defined system fault occurred, the CPU A controller  314  proceeds to display the fault on an LCD display  512  ( FIG. 5B ) (state  1422 ). 
         [0134]    From either state  1420  or  1422  the CPU A controller  314  proceeds to a state  1424  (if flash bit was not enabled) to check the flash enable bit maintained in memory on the CPU B controller  316 . If the flash enable bit is set, the CPU A controller  314  displays a code for flash enabled on the LCD display  512 . The purpose of the flash enable bit is further described in the description for the CPU B controller  316  ( FIG. 16 ). 
         [0135]    From either state  1424  or  1426  (if the flash bit was not enabled), the CPU A controller  314  proceeds to state  1428  and checks for system faults. If the CPU A controller  314  determines that a fault occurred, the CPU A controller  314  displays the fault on the LCD display  512  (state  1430 ). From state  1428  if no fault occurred, or from state  1430 , the CPU A controller  314  proceeds to the checks the system status flag located in the CPU A controller&#39;s memory (decision state  1432 ). If the status flag indicates an error, the CPU A controller  314  proceeds to state  1434  and displays error information on the LCD display  512 . 
         [0136]    From either state  1432  or  1434 , the CPU controller proceeds to state  1402  to repeat the monitoring process. 
         [0137]      FIG. 15  is a flowchart showing one process by which the CPU A controller  314  monitors the fan speed.  FIG. 15  is a more detailed description of the function of state  1412  in  FIG. 14A . Starting in state  1502 , the CPU A controller  314  reads the speed of each of the fans  1506 ,  1508 , and  1510 . The fan speed is processed by a Fan Tachometer Signal Mux  508  (also shown in  FIG. 5B ) which updates the CPU A controller  314 . The CPU A controller  314  then checks to see if a fan speed is above a specified threshold (state  1512 ). If the fan speed is above the threshold, the CPU A controller  314  proceeds to state  1514 . Otherwise, if the fan speed is operating below a specified low speed limit, the CPU A controller  314  proceeds to state  1522 . 
         [0138]    On the other hand, when the fan is operating above the low speed limit at state  1514 , the CPU A controller  314  checks the hot_swap_fan register (not shown) if the particular fan was hot swapped. If the fan was hot swapped, the CPU A controller  314  proceeds to clear the fan&#39;s bit in both the fan_fault register (not shown) and the hot_swap_fan register (state  1516 ). After clearing these bits, the CPU A controller  314  checks the fan fault register (state  1518 ). If the fan fault register is all clear, the CPU A controller  314  proceeds to set the fan to low speed (state  1520 ) and logs a message to the NVRAM  322 . The CPU A controller  314  then proceeds to state  1536  to check for a temperature warning. 
         [0139]    Now, referring back to state  1522 , if a fan speed is below a specified threshold limit, the CPU A controller  314  checks to see if the fan&#39;s speed is zero. If the fan&#39;s speed is zero, the CPU A controller  314  sets the bit in the hot_swap_fan register in state  1524  to indicate that the fan has a fault and should be replaced. If the fan&#39;s speed is not zero, the CPU A controller  314  will proceed to set a bit in the fan_fault register (state  1526 ). Moving to state  1528 , the speed of any fans still operating is increased to high, and a message is written to the NVRAM  322 . 
         [0140]    In one alternative embodiment, the system self-manages temperature as follows: from either state  1520  or  1528 , the CPU A controller  314  moves to state  1536  and checks whether a message was received from the Chassis controller  318  indicating temperature warning. If a temperature warning is indicated, and if there are no fan faults involving fans in the cooling group associated with the warning, the speed of fans in that cooling group is increased to provide more cooling capacity (state  1538 ). 
         [0141]    Proceeding to state  1530  from either state  1536  or  1538 , the CPU A controller  314  increments a fan counter stored inside of microcontroller memory. If at state  1531 , there are more fans to check, the CPU A controller  314  returns to state  1502  to monitor the speed of the other fans. Otherwise, the CPU controller  314  returns to state  1416  ( FIG. 14 ). 
         [0142]      FIG. 16  is one embodiment of a flow diagram showing the functions performed by the CPU B controller  316 . The CPU B controller  316  scans for system faults, scans the microcontroller bus  310 , and provides flash enable. The CPU B controller  316 , starting at state  1600 , initializes its variables and stack pointer. 
         [0143]    After initializing its internal state, the CPU B controller  316  enters a diagnostic loop at state  1602 . The CPU B controller  316  then checks the microcontroller bus  310  for a time out (decision state  1604 ). If the microcontroller bus  310  has timed out, the CPU B controller  316  resets the microcontroller bus  310  in state  1606 . If the microcontroller bus  310  has not timed out (state  1604 ) or after state  1606 , the CPU B controller  316  proceeds to check the system fault register (not shown) (decision state  1608 ). 
         [0144]    If the CPU B controller  316  finds a system fault, the CPU B controller  316  proceeds to log a message into the NVRAM  322  stating that a system fault occurred (state  1610 ). The CPU B controller  316  then sends an event to the System Interface  312  and the Remote Interface  332 . Additionally, the CPU B controller  316  turns on one of a number of LED indicators  518  ( FIG. 5B ). 
         [0145]    If no system fault occurred, or from state  1610 , the CPU B controller  316  scans the microcontroller bus  310  (decision state  1612 ). If the microcontroller bus  310  is hung then the CPU B controller  316  proceeds to flash an LED display  512  that the microcontroller bus  310  is hung (state  1614 ). Otherwise, if the bus is not hung the CPU B controller  316  then proceeds to state  1624 . 
         [0146]    The CPU B controller  316  proceeds to check for a bus stop bit time out (decision state  1624 ). If the stop bit has timed out, the CPU B controller  316  generates a stop bit on the microcontroller bus for error recovery in case the stop bit is inadvertently being held low by another microcontroller (state  1626 ). 
         [0147]    From either state  1624  or  1626 , the CPU B controller  316  proceeds to check the flash enable bit to determine if the flash enable bit (not shown) is set (state  1628 ). If the CPU B controller  316  determines that the flash enable bit is set (by previously having received a message requesting it), the CPU B controller  316  proceeds to log a message to the NVRAM  322  (state  1630 ). A flash update is performed by the BIOS if the system boot disk includes code to update a flash memory (not shown). The BIOS writes new code into the flash memory only if the flash memory is enabled for writing. A software application running on the CPUs  200  can send messages requesting that BIOS flash be enabled. At state  1630 , the 12 Volts needed to write the flash memory is turned on or left turned on. If the flash enable bit is not on, control passes to state  1629 , where the 12 Volts is turned off, disabling writing of the flash memory. 
         [0148]    From either state  1629  or  1630 , the CPU B controller  316  proceeds to repeat the aforementioned process of monitoring for system faults (state  1602 ). 
         [0149]      FIG. 17  is one embodiment of a flowchart showing the functions performed by the Canister controllers  324 ,  326 ,  328  and  330  shown in  FIGS. 4 and 5 . The Canister controllers  324 ,  326 ,  328  and  330  examine canister fan speeds, control power to the canister, and determine which canister slots contain cards. The Canister controllers  324 - 330 , starting in state  1700 , initialize their variables and stack pointers. 
         [0150]    Next, in state  1702  the Canister controllers  324 - 330  start their main loop in which they performs various diagnostics, which are further described below. The Canister controllers  324 - 330  check the microcontroller bus  310  for a time out (state  1704 ). If the microcontroller bus  310  has timed out, the Canister controllers  324 - 330  reset the microcontroller bus  310  in state  1706 . After the Canister controller  324 - 330  reset the microcontroller bus  310 , or if the microcontroller bus  310  has not timed out, the Canister controllers  324 - 330  proceed to examine the speed of the fans (decision state  1708 ). As determined by tachometer signal lines connected through a fan multiplexer  508  ( FIG. 5 ), if either of two canister fans is below the lower threshold, the event is logged, an event is sent to the System Interface  312  and, speed, in a self-management embodiment, the fan speed is set to high. The Canister controllers  324 - 330  check the fan speed again, and if they are still low the canister controlling  324 - 330  signal a fan fault and register an error message in the NVRAM  322  (state  1710 ). 
         [0151]    If the Canister controller received a request message to turn on or off canister power, a bit would have been previously set. If the Canister controllers  324 - 330  find this bit set (state  1712 ), they turn the power to the canister on, and light the canister&#39;s LED. If the bit is cleared, power to the canister is turned off, as is the LED (state  1714 ). 
         [0152]    Next, the Canister controllers  324 - 330  read a signal for each slot which indicates whether the slot contains an adapter (state  1716 ). The Canister controllers  324 - 330  then returns to the state  1702 , to repeat the aforementioned monitoring process. 
         [0153]      FIG. 18  is one embodiment of a flowchart showing the functions performed by the System Recorder controller  320 . The System Recorder controller  320  maintains a system log in the NVRAM  322 . The System Recorder  320  starting in state  1800  initializes its variables and stack pointer. 
         [0154]    Next, at state  1802  the System Recorder  320  starts its main loop in which the System Recorder  320  performs various functions, which are further described below. First, the System Recorder  320  checks the microcontroller bus  310  for a time out (state  1804 ). If the microcontroller bus  310  has timed out, the System Recorder  320  resets the microcontroller bus  310  in state  1806 . After the System Recorder  320  resets the bus, or if the microcontroller bus  310  has not timed out, the System Recorder  320  checks to see if another microcontroller had requested the System Recorder  320  to reset the NVRAM  322  (state  1808 ). If requested, the System Recorder  320  proceeds to reset all the memory in the NVRAM  322  to zero (decision state  1810 ). After resetting the NVRAM  322 , or if no microcontroller had requested such a reset, the System Recorder  320  proceeds to a get the real time clock every second from a timer chip  520  ( FIG. 5A ) (decision state  1812 ). 
         [0155]    From time to time, the System Recorder  320  will be interrupted by the receipt of messages. When these messages are for storing data in the NVRAM  322 , they are carried out as they are received and the messages are stored in the NVRAM  322 . Thus, there is no state in the flow of  FIG. 18  to explicitly store messages. The System Recorder then returns to the state  1802  to repeat the aforementioned monitoring process. 
         [0156]    While the above detailed description has shown, described, and pointed out the fundamental novel features of the invention as applied to various embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the system illustrated by be made by those skilled in the art, without departing from the intent of the invention.