Patent Abstract:
A system and method for a software override capability for enforcing a predetermined state for an otherwise hardware-programmable device. Software that may think it knows what it is doing may try to control a hardware device, but may not know about a hardware issue, such as another feature or defect requiring that the device stay in a certain state. The technique programmatically maintains a persistent hardware state independent of any other control software. To other software, the software layer of the invention is indistinguishable and inseparable from hardware. Nothing can slip in between. Any insertion attempt will be detected and disallowed. Features of the processor or system chips actually weld the software to the hardware, which feature disallows any software intervention between the welded software layer and the hardware. Various uses for this method may include making hardware persistently behave in a given fashion, in spite of ongoing attempts from other software to reconfigure the hardware behavior. This may provide a software-only solution to a hardware defect. One may extend hardware capability without replacing hardware, and without concern for insertion of other software layers that would alter states impermissibly if allowed to obtain conventional access, such as I/O port commands, memory-mapped I/O commands. Monitoring capability of access and control of an underlying hardware interface is also available.

Full Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 09/571,969 filed May 16, 2000 and entitled SOFTWARE-HARDWARE WELDING SYSTEM. 
     
    
     
       BACKGROUND  
         [0002]    1. The Field of the Invention  
           [0003]    This invention relates to software programming for controlling behavior of hardware devices, and, more particularly, to novel systems and methods for inseparably welding a software layer to a hardware device interface, thus precluding insertion of any other software layer therebetween.  
           [0004]    2. Background of the Invention  
           [0005]    Computers are now used to perform functions and maintain data critical to many organizations. Businesses use computers to maintain essential financial and other business data. Computers are also used by government to monitor, regulate, and even activate, national defense systems. Maintaining the integrity of the stored data is essential to the proper functioning of these computer systems, and data corruption can have serious (even life threatening) consequences.  
           [0006]    Most computer systems include media drives, such as floppy diskette drives for storing and retrieving data. For example, an employee of a large financial institution may have a personal computer that is attached to the main system. In order to avoid processing delays on the mainframe, the employee may routinely transfer data files from a host system to a local personal computer and then back again, temporarily storing or backing up data on a local floppy diskette or other media. Similarly, an employee with a personal computer at home may occasionally decide to take work home, transporting data away from and back to the office on a floppy diskette.  
           [0007]    Data transfer to and from media, such as a floppy diskette, is controlled by a device called a Floppy Diskette Controller (“FDC”). The FDC is responsible for interfacing the computer&#39;s Central Processing Unit (“CPU”) with a physical media drive. Significantly, since the drive is spinning, it is necessary for the FDC to provide data to the drive at a specified data rate. Otherwise, the data will be written to a wrong location on the media.  
           [0008]    The design of an FDC accounts for situations occurring when a data rate is not adequate to support rotating media. Whenever this situation occurs, the FDC aborts the write operation and signals to the CPU that a data under run condition has occurred.  
           [0009]    Unfortunately, however, it has been found that a design flaw in many FDCs makes impossible the detection of certain data under run conditions. This flaw has, for example, been found in the NEC 765, INTEL 8272 and compatible Floppy Diskette Controllers. Specifically, data loss and/or data corruption may routinely occur during data transfers to or from diskettes (or tape drives and other media attached via the FDC), whenever the last data byte of a sector being transferred is delayed for more than a few microseconds. Furthermore, if the last byte of a sector write operation is delayed too long then the next (physically adjacent) sector of the media will be destroyed as well.  
           [0010]    For example, it has been found that these faulty FDCs cannot detect a data under run on the last byte of a diskette read or write operation. Consequently, if the FDC is preempted or otherwise suspended during a data transfer to the diskette (thereby delaying the transfer), and an under run occurs on the last byte of a sector, the following occur: (1) the under run flag does not get set, (2) the last byte written to the diskette is made equal to either the previous byte written or zero, and (3) a successful Cyclic Redundancy Check (“CRC”) is generated on the improperly altered data. The result is that incorrect data is written to the diskette and validated by the FDC. Herein, references to a floppy diskette may be read as “any media” and a floppy diskette drive is but a specific example of a media drive controllable by an FDC.  
           [0011]    Conditions under which this problem may occur have been identified in connection with the instant invention by identifying conditions that can delay data transfer to or from the diskette drive. In general, this requires that the computer system be engaged in “multi-tasking” operation or in overlapped input/output (“I/O”) operation. Multi-tasking is the ability of a computer operating system to simulate the concurrent execution of multiple tasks.  
           [0012]    Importantly, concurrent execution is only “simulated” because only one CPU exists in a typical personal computer. One CPU can only process one task at a time. Therefore, a system interrupt is used to rapidly switch between the multiple tasks, giving the overall appearance of concurrent execution.  
           [0013]    MS-DOS and PC-DOS, for example, are single-task operating systems. Therefore, one could argue that the problem described above would not occur. However, a number of standard MS-DOS and PC-DOS operating environments simulate multi-tasking and are susceptible to the problem.  
           [0014]    In connection with the instant invention, for example, the following environments have been found to be prime candidates for data loss and/or data corruption due to defective FDCs: local area networks, 327x host connections, high density diskettes, control print screen operations, terminate and stay resident (“TSR”) programs. The problem also occurs as a result of virtually any interrupt service routine. Thus, unless MS-DOS and PC-DOS operating systems disable all interrupts during diskette transfers, they are also highly susceptible to data loss and/or corruption.  
           [0015]    The UNIX operating system is a multi-tasking operating system. It has been found, in connection with the instant invention, how to create a situation that can cause the problem within UNIX. One example is to begin a large transfer to the diskette and place that transfer task in the background. After the transfer has begun then begin to process the contents of a very large file in a way that requires the use a Direct Memory Access (“DMA”) channel of a higher-priority than that of the floppy diskette controller&#39;s DMA channel. These might include, for example, video updates, multi-media activity, etc. Video access forces the video buffer memory refresh logic on DMA channel  1 , along with the video memory access, which preempts the FDC operations from occurring on DMA channel  2  (which is lower priority than DMA channel  1 ).  
           [0016]    This type of example creates an overlapped I/O environment and can force the FDC into an undetectable error condition. More rigorous examples include a concurrent transfer of data to or from a network or tape drive using a high priority DMA channel while the diskette transfer is active. Clearly, the number of possible error producing examples is infinite, yet each is highly probable in this environment.  
           [0017]    For all practical purposes the OS/2 and newer Windows operating systems can be regarded as UNIX derivatives. They suffer from the same problems that UNIX does. Two significant differences exist between these operating systems and UNIX.  
           [0018]    First, they both semaphore video updates with diskette operations tending to avoid forcing the FDC problem to occur. However, any direct access to the video buffer, in either real or protected mode, during a diskette transfer will bypass this feature and result in the same faulty condition as UNIX.  
           [0019]    Second, OS/2 incorporates a unique command that tends to avoid the FDC problem by reading back every sector that is written to the floppy diskette in order to verify that the operation completed successfully. This command is an extension to the MODE command (MODE DSKT VER=ON). With these changes, data loss and/or data corruption should occur less frequently than otherwise. However, the FDC problem may still destroy data that is not related to the current sector operation.  
           [0020]    A host of other operating systems are susceptible to the FDC problem just as DOS, Windows, Windows 95, Windows 98, Windows NT, OS/2, and UNIX. However, these systems may not have an installed base as large as DOS, Windows, OS/2 or UNIX, and may, therefore, receive less motivation to address the problem. Significantly, as long as the operating systems utilize the FDC and service system interrupts, the problem can manifest itself. This can occur in computer systems that use virtually any operating system.  
           [0021]    Some in the computer industry have suggested that data corruption by the FDC is extremely rare and difficult to reproduce. This is similar to the argument presented during the highly publicized 1994 defective INTEL Pentium scenario. Error rate frequencies for the defective Pentium ranged from microseconds to tens-of-thousands of years! The FDC problem is often very difficult to detect during normal operation because of its random characteristics. The only way to visibly detect this problem is to have the FDC corrupt data that is critical to the operation at hand. However, many locations on the diskette may be corrupted, yet not accessed. In connection with the instant invention, the FDC problem has been routinely reproduced and may be more common than heretofore believed.  
           [0022]    Computer users may, in fact, experience this problem frequently and not even know about it. After formatting a diskette, for example, the system may inform the user that the diskette is bad, although the user finds that if the operation is performed again on the same diskette everything is fine. Similarly, a copied file may be unusable, and the computer user concludes that he or she just did something wrong. For many in this high-tech world, it is very difficult to believe that the machine is in error and not themselves. It remains typical, however, that full diskette back-ups are seldom restored, that all instructions in programs are seldom, if ever, executed, that diskette files seldom utilize all of the allocated space, and that less complex systems are less likely to exhibit the problem.  
           [0023]    Additionally, the first of these faulty FDCs was shipped in the late 1970&#39;s. The devices were primarily used at that time in special-purpose operations in which the FDC problem would not normally be manifest. Today, on the other hand, the FDCs are incorporated into general-purpose computer systems that are capable of concurrent operation (multi-tasking or overlapped I/O). Thus, it is within today&#39;s environments that the problem is most likely to occur by having another operation delay a data transfer to a diskette. The more complex a computer system, the more likely it is that one activity will delay another, thereby creating an FDC error condition.  
           [0024]    In short, the potential for data loss and/or data corruption is present in all computer systems that utilize the defective version of this type of FDC, presently estimated at about 50 million personal computers. The design flaw in the FDC causes data corruption to occur and manifest itself in the same manner as a destructive computer virus. Furthermore, because of its nature, this problem has the potential of rendering even secure databases absolutely useless.  
           [0025]    Moreover, more recent FDC devices may be affected by the use of first-in-first-out (FIFO) devices that alter the usual operation. Whenever the FIFO is enabled, detection of the defective controller may be well nigh impossible. Nevertheless, when the FIFO is not enabled, due to the vagaries of some particular operating system or device driver, the defect may appear and cause data corruption.  
           [0026]    Various conventional ways of addressing the FDC problem, such as a hardware recall, have significant associated costs, risks and/or disadvantages. In addition to a solution to the FDC problem, an apparatus and method are needed to accurately, rapidly, reliably, and correctly, identify any defective FDC. The identification of defective FDCs is the first step in attempting to solve the problem of defective FDCs. A solution method and apparatus for repairing a defective FDC are disclosed in U.S. Pat. No. 5,379,414 incorporated herein by reference.  
         BRIEF SUMMARY AND OBJECTS OF THE INVENTION  
         [0027]    In view of the foregoing, it is a primary object of the present invention to provide a method and apparatus for detecting defective Floppy Diskette Controllers (“FDCs”).  
           [0028]    It is another object of the present invention to provide a software (programmatic) solution that may be implemented in a general purpose digital computer, which eliminates the need for visual inspection and identification of the defective FDCs as well as the need for any hardware recall and replacement.  
           [0029]    Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, an apparatus and method are disclosed in one embodiment of the present invention as including data structures, executable modules, and hardware, implementing a detection method capable of immediately, repeatedly, correctly, and accurately detecting defective FDCs.  
           [0030]    The apparatus and method may rely on 1) determining whether or not the FDC under test is a new model FDC (potentially non-defective), and 2) if the FDC under test is not a new model FDC, installing an interposer routine to force the FDC to delay a transfer of a last data byte of a sector either to or from the floppy diskette whose controller is tested. A test condition is thus created in the hardware to cause defective FDCs to corrupt the last data byte of the sector. A second portion of an apparatus and method may confirm a diagnosis. Thus the apparatus and method may ensure that old-model non-defective FDCs are not wrongly identified as defective.  
           [0031]    Chips manufactured in recent years may have the data corrupting defect originally identified. Nevertheless, the defect may manifest itself in other ways. Meanwhile, the three needs remain. The failure of the chip needs to be detected, including navigation of the masking features that may limit an ability to detect FIFO-enabled chips. Second, correction of the defect in hardware, by using a software solution is needed. Finally, detection of corruption resulting from previous failures of a FIFO-enabled chip to detect errors will be required.  
           [0032]    A system and method in accordance with the invention may be implemented to provide a software override capability for enforcing a predetermined state for an otherwise hardware-programmable device. Software that may think it knows what it is doing may try to control a hardware device, but may not know about a hardware issue, such as another process or a defect requiring that the device remain in a certain state.  
           [0033]    The technique programmatically maintains a persistent hardware state independent of any other control software. To other software, the software layer of the invention is indistinguishable and inseparable from hardware. Nothing can slip in between. Anything insertion attempt will be detected and disallowed. Features of the processor or system chips actually weld the software to the hardware, which disallows any software intervention between the welded software layer and the hardware.  
           [0034]    Various uses for this method may include making hardware persistently behave in a given fashion, in spite of ongoing requests from other software to reconfigure the underlying hardware behavior. This may provide a software-only solution to a hardware defect. One may extend hardware capability without replacing hardware, and without concern for insertion of other software layers that would program performance impermissibly if allowed to obtain conventional access, such as I/O port commands, memory-mapped I/O commands. Monitoring capability of access and control of an underlying hardware interface is also available.  
           [0035]    One application of a method in accordance with the invention may provide a complete software implementation of overriding a detection process that is capable of detecting defective Floppy Diskette Controllers (“FDCs”) without visual hardware inspection or identification. The approach taken includes a multi-phase strategy incorporating programmatic FDC identification, software DMA shadowing, defect inducement, and use of a software decoding network, all of which allows the implementation of the invention to adjust to a wide range of computer system performance levels.  
           [0036]    A method and apparatus for detecting and preventing floppy diskette controller data transfer errors in computer systems is also provided. The approach taken may involve software DMA shadowing and the use of a software decoding network.  
           [0037]    In certain embodiments, an apparatus for detecting a defective floppy diskette controller may comprise a computer readable medium storing executable and operational data structures. The data structures may include a determination module for identifying a hardware resource associated with a computer system, a welding module for inseparably connecting a persistent software layer to the hardware resource, and a defense module for resisting attempts by other software to unweld the persistent software layer from the hardware resource.  
           [0038]    The apparatus may store data structures including a function module for performing a desired function whenever the hardware resource is accessed by the computer system. The function module may be configured to control the hardware resource to provide a function otherwise unavailable from the hardware resource as manufactured. The data structures may include an unweld module for disconnecting the persistent software layer from the hardware resource. The unweld module may be configured to be embedded in the welding module.  
           [0039]    In at least one embodiment, a computer readable medium storing data structures may embody steps for effecting a method providing a computer system comprising a processor operably connected to a first hardware resource. It may include installing a driver corresponding to the first hardware resource, and including a resource identifier for identifying available hardware resources. Further the method may include identification of the processor, by the resource identifier, the first hardware resource and executing, on the processor, a welder to inseparably connect a persistent software layer.  
           [0040]    The method may include accessing, by the processor, a first hardware interface and automatically engaging the persistent software layer upon accessing, by the processor, to the hardware interface. The method may provide a defense module for responding to attempts to unweld the persistent software layer from the first hardware interface, and provide a controller for controlling the first hardware resource.  
           [0041]    The persistent software layer may have a function module, executable to perform an extension function, the extension function being beyond the inherent functionality of the controller. The extension function may have a function lock for overriding requests from other software to reconfigure the functionality of the first hardware resource. The function module may be configured to perform a function selected from detection and correction of a hardware defect in the controller.  
           [0042]    The function module may be configured to extend the functional capability of at least one of the first hardware resource and the controller, without replacement thereof. The function module may be configured to monitor at least one of access and control of at least one of the first hardware device and the controller.  
           [0043]    In one embodiment, a method for welding a software layer to a hardware layer in a computer system having hardware interfaces may include providing a computer system comprising a processor operably connected to a first hardware resource., with a first hardware interface corresponding to the first hardware resource. Then, the method may install a driver corresponding to the first hardware resource, and including a resource identifier for identifying available hardware resources. After identifying the first hardware resource, the method may execute on the processor a welder for inseparably connecting a persistent software layer.  
           [0044]    The method may include accessing, by the processor, the first hardware interface; and automatically engaging the persistent software layer upon accessing, by the processor, the hardware interface. The persistent software layer may have included a function module configured to monitor at least one of access and control of at least one of the first hardware device and the controller. Inseparably connecting may result in rendering the connection unbreakable by other than the welder. Typically it will render substantially impossible an insertion of an executable between the first hardware resource and the persistent software layer.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0045]    The foregoing and other objects and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which:  
         [0046]    [0046]FIG. 1 is a schematic block diagram of an apparatus illustrating the architecture of a computer system for testing a floppy diskette controller (“FDC”)in accordance with the invention;  
         [0047]    [0047]FIG. 2 is a schematic block diagram illustrating software modules executing on the processor and stored in the memory device of FIG. 1, including application programs, operating systems, device drivers and computer system hardware such as a floppy diskette;  
         [0048]    [0048]FIG. 3 is a schematic block diagram of a flow chart depicting one presently preferred embodiment of certain modifications that may be applied to a diskette device driver in order to force an otherwise undetected error condition to occur in a defective FDC, thus enabling the defective FDC detection apparatus and method of the present invention to be activated;  
         [0049]    [0049]FIG. 4 is a schematic block diagram of a flow chart depicting one presently preferred embodiment of certain modifications that may be made to a timer Interrupt Service Routine (“ISR”) to allow timing of a transfer byte&#39;s DMA request and DMA acknowledge (DREQ/DACK) cycle in order to ensure that proper conditions exist to create data corruption associated with defective FDCs in accordance with the present invention;  
         [0050]    [0050]FIG. 5 is a schematic block diagram of a flow chart depicting one presently preferred embodiment of a software decoding network (software vector-table) for use in connection with a defective FDC detection apparatus and method in accordance with the present invention, the software decoding network having one code point/entry for each possible transfer byte in a sector;  
         [0051]    [0051]FIG. 6 is a schematic block diagram of a flow chart depicting one presently preferred embodiment of an application implementation of the apparatus and method of FIGS. 3 and 4, wherein a main “driver” portion of an application forces an undetected error condition in a defective FDC enabling activation of a the defective FDC detection system in accordance with the invention;  
         [0052]    [0052]FIG. 7 is a schematic block diagram of a flow chart depicting one presently preferred embodiment of certain modifications that may be made to a timer Interrupt Service Routine embedded within the application of FIG. 6 to allow timing of a last byte&#39;s DREQ/DACK cycle, ensuring that proper conditions exist to create data corruption associated with defective FDCs in accordance with the present invention.  
         [0053]    [0053]FIG. 8 is a schematic block diagram of a method for welding a software layer to a hardware layer in accordance with the invention;  
         [0054]    [0054]FIGS. 9A and 9B are schematic block diagrams of details corresponding to an instruction not to install, as resulting from the process of FIG. 8;  
         [0055]    [0055]FIG. 10 is a schematic block diagram of a method for a shadowing hardware layer interface access;  
         [0056]    [0056]FIG. 11 is a schematic block diagram of a method for eliminating attempts by other software to unweld the connection between a persistent software module and the hardware;  
         [0057]    [0057]FIG. 12 is a schematic block diagram of a method for performing a desired persistent function in accordance with the invention;  
         [0058]    [0058]FIG. 13 is a schematic block diagram of the details of a check command in accordance with the invention;  
         [0059]    [0059]FIG. 14 is a schematic block diagram of more command bytes that may be provided in accordance with the embodiment of FIG. 1;  
         [0060]    [0060]FIG. 15 is a schematic block diagram of a method for unwelding the persistent software layer from the hardware layer upon completion of the need for the functionality thereof; and  
         [0061]    [0061]FIG. 16 is a schematic block diagram of a process for ordering the reading of the least and most significant bytes in a critical region. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0062]    It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system apparatus and method of the present invention, as represented in FIGS. 1 through 15, is not intended to limit the scope of the invention, as claimed, but it is merely representative of the presently preferred embodiments of the invention.  
         [0063]    The presently preferred embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.  
         [0064]    The architecture of an apparatus  10 , including a computer system implementing one embodiment of the invention, is illustrated in FIG. 1. A Central Processing Unit (“CPU”)  12  and main memory  14  may be connected by a bus  15  inside a computer system unit. Instructions (executables) and data structures used by the CPU  12  are kept in main memory  14  during computer work sessions. Main memory  14  is, however, not a permanent storage place for information; it is active only when the apparatus  10  (computer system) is powered up (on). Thus, to avoid losing data, data must be saved on some type of non-volatile storage device. For example, the apparatus may use a “hard disk” storage device permanently installed in the computer system. A computer system  10  may have at least one floppy diskette drive  16  that receives a removable floppy diskette (magnetic storage medium). The floppy diskette likewise may be used for “permanent” (non-volatile) storage of data or software (executables) outside of the computer system  10  flexible (floppy) diskettes are especially useful for transferring data and information between separate computer systems  10 .  
         [0065]    In transferring data to a floppy diskette, the CPU  12  may program a Direct Memory Access (“DMA”) controller  18  for an input/output (“I/O”) transfer. The CPU  12  issues a command to a Floppy Diskette Controller (“FDC”)  20  to begin the I/O transfer, and then waits for the FDC  20  to interrupt the CPU  12  with a completion interrupt signal. It is also possible to perform Programmed I/O (“PIO”) directly between the CPU  10  and the FDC  20  without involving the DMA controller  18 . This latter approach is seldom used; the majority of computer systems  10  employ DMA for I/O transfers to and from the floppy diskette drive  16 . The invention will thus be described below with particular reference to the DMA controller  18 . If PIO is employed, however, then an I/O transfer is totally controlled by the CPU  12  because the CPU  12  is required to pass each and every data byte to the FDC  16 . As a result, the “DMA shadowing” system and method in accordance with the invention may be directly applied to a PIO data stream. This is readily tractable because the CPU  12  already is controlling the I/O transfer, as will become more readily apparent.  
         [0066]    A computer system  10  may have a system clock  22 . The system clock  22  is beneficial when initiating an I/O transfer to the diskette drive  16  because one must not only control the data transfer, but also a drive motor. In this regard, it is important to know when the diskette drive motor has brought a diskette&#39;s spin rate up to a nominal RPM required for a data transfer to be successful.  
         [0067]    For example, in IBM Personal Computers and “compatibles,” the system clock  22  interrupts the CPU  12  at a rate of 18.2 times per second (roughly once every 54.9 milliseconds). This interrupt is used to determine such things as diskette drive motor start and stop time. There are also a host of other time-dependent operations in the computer system  10  that require this granularity of timing.  
         [0068]    One presently preferred embodiment of an association between application programs  24  (executables), operating systems  26 , device drivers and hardware is depicted in FIG. 2. The example presented corresponds to a floppy diskette having a controller  16 .  
         [0069]    A system suitable for implementing the invention may include an application program  24  including both executable code  25   a  and associated data  25   b . The application  24  may interface with the hardware apparatus  10  through an operating system  26 . The operating system may include a file system  27   a  as well as selected buffers  27   b.  The file system  27   a  may include an executable for file system management as well as operating system interfacing. The file system  27   a  may issue commands to drivers  28 .  
         [0070]    The drivers  28  may include a timer device driver  29   a,  including a timer ISR, interfacing to the system clock  22 . Likewise, a media drive driver  29   b,  alternatively referred to as a media driver  29   b  may be included. The media driver may interface with a floppy diskette drive or other media drive  16  to maintain persistent storage on media  17 . Although a media drive  16  may typically relate to floppy diskettes, tape drives and other magnetic media may also be used in an apparatus and method in accordance with the invention.  
         [0071]    The media driver  29   b  may be responsible for sending instructions and control signals to the media drive controller  20 , which is typically embodied as a floppy diskette controller  20 . Similarly, the media driver  29   b  may instruct and control the DMA controller  18 . The DMA controller manages data transfers between the floppy diskette controller (FDC  20 ) and the main memory device  14 . A DMA request (DRQ; DREQ  21   a ) may pass from FDC controller  20  to the direct memory access controller  18  (DMA controller  18 ). Likewise, a DMA acknowledge  21   b  or acknowledgment  21   b,  alternatively referred to as a (DACK  21   b ) may be returned from the DMA controller  18  to the FDC  20 .  
         [0072]    Referring now to FIGS.  3 - 5 , and more particularly FIGS. 3 and 4, a method in accordance with the present invention include a module  32 , one of several interposer routines  34 , which is placed between an application&#39;s  24  request  36  for floppy service and a floppy device driver  29   b.  The interposer routine  32  is actually a new or modified device driver that forces certain undetected FDC data corruption conditions to exist. As shown, the interposer  32  first tests  40  whether an operation requested  36  is a floppy diskette write operation. Read operations are equally susceptible to the problem and may be used in the detection process, if desired. If so, the major function of the interposer  32  is to insert itself between the application request  36  for floppy service and the floppy device driver  29   b  that will service the request. In a PC/MS-DOS environment, this can be accomplished by “hooking” the INT 0×13 interrupt vector and directing it to the FDD prefix  32  or interposer routine  32 . Reprogramming  44  the timer  22  to interrupt faster (e.g., every 4-7 milliseconds) than normal (e.g. 54.9 milliseconds).  
         [0073]    As will become more fully apparent from the following discussion, once a floppy write operation is detected, in a test  40  a software decoding network call vector of the timer interrupt  54  (see FIGS.  4 - 5 ) is preferably installed. The current byte count is read  56 , and DMA shadowing  58  begins. When a test  58  shows that a current DMA transfer count (countdown) has reached 0, then the interposer routine  54  delays  60  the DMA transfer of the last byte of the sector transfer. The delay continues until a test  62  determines that the elapsed time is greater than the maximum time required for a data byte to be transferred to the medium  17  (e.g. a low-density diskette; &gt;32 uSec).  
         [0074]    This delay  60  forces defective FDCs  20  into an undetected data corruption condition. This condition can be tested  120  by reading back  118  the written data to see whether the last byte or the next-to-the-last byte was actually written to the last byte location of the sector.  
         [0075]    Referring again to FIG. 3, the system clock  22  may be reprogrammed  50  in a suffix routine  46  appended to the floppy device driver  29   b.  The system clock  22  may then interrupt normally (e.g., every 54.9 milliseconds). The timer interrupt  54  is “unhooked”  50  until the test  40  reports the next floppy write operation.  
         [0076]    One could allow the timer  22  (clock  22 ) to always interrupt at the accelerated rate. Then, a check the timer Interrupt Service Routine (“ISR”)  29   c  (see FIG. 4), within the timer device driver  29   a,  may then determine whether a media (e.g. diskette) write operation is active. Likewise, it is possible to randomly check to see if the last byte of a floppy sector write operation is in progress. However, the foregoing method has superior efficiency and accuracy in creating the condition required for the detection of defective FDCs.  
         [0077]    As used herein, “DMA shadowing” may be thought of as programmatic CPU  12  monitoring of data (byte) transfers and timing the last byte of a sector&#39;s DREQ  21   a  to DACK  21   b  signals. Importantly, there are, of course, a number of ways of determining when the DREQ  21   a  is present and when the DACK  21   b  is present. The present invention may include the use of any “DMA shadowing” whether the DREQ  21   a  and DACK  21   b  signals are detected at the DMA controller  18 , CPU  12 , system bus  15  or FDC  20 . This includes both explicit means, and implicit means.  
         [0078]    For example, inferring the state of the DREQ/DACK cycle is possible from various components in the system that are triggered or reset from transitions of such signals  21   a,    21   b.  In one embodiment the DACK  21   b  may cause a Terminal Count (“TC”) signal to be asserted by the DMA controller  18 . Therefore, one may imply from the detection of the TC that a DACK  21   b  has occurred.  
         [0079]    Whenever an application  24  requests a write operation of the media drive  16 , the system clock  22  may be reprogrammed to interrupt, for example, every 4 to 7 milliseconds. Referring again to FIGS.  4 - 5 , each time the system clock  22  interrupts, the current byte count in the transfer register (countdown register) DMA controller  18  is read  56 . Once the test  58  indicates that the byte counter has reached the last byte, the signal transition from DREQ  21   a  to DACK  21   b  may be timed and accordingly delayed  60 . This transition may be forced to be greater than the maximum time required to transfer one data byte as indicated in the test  62 .  
         [0080]    Therefore, defective FDCs  20  are forced into an undetected data corruption state. This state may be detected by writing known data patterns to the next-to-the-last and the last data bytes. Reading the data back will reveal which of the two data bytes was stored in the last byte of the sector. Finally, it is possible to also detect defective FDCs  20  by significantly increasing the delay time during the transfer of the last byte of a sector. This forces the next physically adjacent sector to be zeroed out except for the first byte of that sector.  
         [0081]    For the system to maintain proper operation, an interposer routine  34  should save the original INT 0×13 (Hex 13th interrupt vector) contents (address of the original INT 0×13 Interrupt Service Routine) and invoke the original when necessary. Additional aspects of the interposer function  34  are discussed below in connection with other features of the device driver  29   b.    
         [0082]    This implementation of the apparatus and method of the present invention is contemplated for use on an IBM Personal Computer running the PC/MS-DOS operating system. Versions have, however, been developed to operate in the Windows, OS/2 and UNIX environments and maybe embodied for other operating systems. The invention is not limited to use with any particular operating system, and adaptations and changes which may be required for use with other operating systems will be readily apparent to those of ordinary skill in the art.  
         [0083]    As depicted graphically in FIG. 4 below, a timer ISR routine  29   c  is used for servicing the accelerated interrupt rate of the system clock  22 . The reason that the system clock interrupt rate is accelerated is that during a normal 512 byte data transfer (the typical sector size) 16 microseconds are required for each data byte to be transferred to the FDC (High Density Diskette Mode). Therefore, a typical sector transfer requires 512 times 16 microseconds, or 8,192 microseconds. If the diskette is a low density diskette then the sector transfer time is doubled to 16,384 microseconds (512 times 32 microseconds) because the FDC has half of the amount of data to store in the same rotational time frame (typically 360 RPM).  
         [0084]    Referring to FIG. 5, the timer ISR routine  29   c  within the timer device driver  29   a  with its prefix  54  performs checks on the system  10  to determine if the system  10  is actually transferring data to the FDC  20 . If a sector transfer is not in progress then the timer ISR prefix  54  exits immediately. However, if a sector transfer is in progress then the timer ISR prefix  54  obtains the remaining byte count of the sector transfer  70  and vectors (jumps) through the software decoding network  72  (DMA count table  72 ) to an appropriate processing routine  84 ,  86 ,  88 .  
         [0085]    Although the steps  56 ,  58  of the module  54  may be implemented with the timer  22  continually interrupting every 8, 16, or 32 microseconds. This level of interrupts may totally consume a PC&#39;s processing power, and on most PCs could not be sustained. Thus, in order to perform DMA shadowing without affecting the total system performance it is important to allow normal operations to continue as usual. It is desirable to have an interrupt (the system clock  22 ) that will interrupt close to the end of the sector transfer so that the DREQ  21   a  to DACK  21   b  timing may be determined on the last byte of the sector transfer.  
         [0086]    Thus, it is possible to DMA shadow  58  all 512 bytes during a sector transfer, but that would cause the CPU to be totally consumed during the entire sector transfer time. The potential of losing processing activities elsewhere in the system are greatly increased, as in serial communications. Therefore, the clock interrupt routine  29   c  or method  29   c  of FIG. 5 may reduce the CPU involvement to a bare minimum during those floppy write operations with DMA Shadowing. Significantly, the timing may be adjusted to any number of bytes of a sector transfer, from a few bytes to the entire sector count.  
         [0087]    One operation performed in the timer ISR routine  29   c  is to vector through the software decoding network  72  to the appropriate processing routine  84 ,  86 ,  88 . This process is illustrated graphically in FIG. 5. The software decoding network  72  (software vector-table  72 ) has one code point/entry  74 ,  80 ,  82  for each possible transfer byte in the sector.  
         [0088]    The timer interrupt rate can now be in terms of 10&#39;s or 100&#39;s of byte transfer times. The vector table  72  may cause the program execution of the CPU  12  to enter a cascade  86  of DREQ  21   a /DACK  21   b  checks only when the transfer (sector) will complete prior to the next timer interrupt. In short, the first entries  74  in the vector table  72  will return  84 , since another timer interrupt will occur before the sector transfer completes. The latter entries  80 , within the desired range, will cascade  86  from one DREQ  21   a /DACK  21   b  detection to another (shadowing  58  the DMA transfers) until the last byte is transferred.  
         [0089]    On the last byte being transferred, the data byte may be delayed by either activating a higher priority DMA  18  channel or masking the DMA channel of the FDC  20 . Although these two techniques are the simplest to program, numerous alternatives may be used to delay  60  data transfers on the DMA  18  channel of the FDC  20 , in accordance with the invention.  
         [0090]    This software decoding network process  54  is the fastest known software technique for decoding and executing time-dependent situations. Space in the memory space  14  (e.g. the software decoding network vector table  72 ) is traded for processing time, the amount of time it would take for one routine to subsume all functionality encoded in each of the routines  84 ,  86 ,  88  vectored to through the software decoding network vector table  72 .  
         [0091]    As indicated above, the entire software decoding network table  72  may be initially set to the address of an “exiting routine  84 .” Then depending upon how slow or fast the system clock  22  interrupts, a certain number of the lower-indexed entries  80  of the table  72  may be set to the address of a processing routine  86 . These processing routines  86  may be identical and sequentially located in the routine  54 . Thus, the software decoding network vector table  72  may simply vector the timer ISR routine  29   c  within the driver  29   a  to the first of n sequentially executed processing routines. Here, n represents the number of bytes remaining in the sector transfer. In this way the last few bytes of the sector transfer can be accurately monitored (DMA Shadowing  58 ) without significantly affecting overall system performance.  
         [0092]    Each of the processing routines  86 , except the last one  88 , may perform exactly the same function. It is not necessary to be concerned with the timing between the DREQ  21   a  and DACK  21   b  signals until the very last data byte of a transfer. Therefore, the routines  86 ,  88  above “shadow”  58  the operation of the DMA until the last byte (e.g. corresponding to entry  82  of the vector  72 ) at which time the DMA channel of the FDC  20  is delayed as previously described.  
         [0093]    Thus, through software DMA shadowing, it is possible to reliably determine when the last byte of the transfer is about to be transferred. Therefore, it is possible to force the last databyte&#39;s transfer to be delayed. An alternative approach may include a specialized application program  24  to control all aspects of the operation of the media drive  16 , e.g. floppy diskette drive  16 . This may include a transfer delay of a last byte, as indicated in FIGS.  6  (main application) and  7  (timer interrupt service routine). All aspects of the previous approach may be present. However, here they may be collected into a single application program  24  performing the required functions. The application program  24  may reprogram the system clock to interrupt at an accelerated rate and services the interrupt itself. The application program may then begin a repeated set of diskette write operations using the BIOS interface interrupt (Ox13) and then read the written sectors back. Once the sector has been written and read back the data is compared to determine whether or not an undetected error has occurred. A running total of both detected and undetected errors may be output to a display.  
         [0094]    Referring now to FIG. 6, an application  24  may include steps  110 - 117 . Alternatively, preprocessing may begin at an entry point  100  leading to an initial command  102 . Command  102  is effective to request of a floppy diskette controller (FDC)  20  an identification. A status return of 0×90 (hexadecimal 90) should indicate that a FDC  20  is not of the type that is per se defective. However, faulty programming has now falsified the response fed to the test  104  in certain chips. Therefore, the command  102  may give rise to a false status return of 0×90 hexadecimal 90. This return does not guarantee that an FDC  20  is not defective.  
         [0095]    Thus, a test  104  does not actually determine whether or not the status of an FDC  20  is defective. A negative response instead may be saved  105  to establish false negative responses programmed in by manufacturers. The display step  106  may include selected post processing to output results of the application  24 . Results may include, for example, an indication of whether the FDC  20  being tested is defective or not and whether a false negative response was given to test  104 , in view of the results of the test  112 . Accordingly, a status not equal to a hex 80 would ordinarily result in the test  104  signifying that an FDC  20  is not defective. The steps  105 ,  106  thereafter verify defectiveness and improper circumvention of the test  104 .  
         [0096]    After to the test  104 , the application  24  advances to a hook  110 . The hook  110  is effective to interpose a timer prefix  124  (see FIG. 7) corresponding the prefix  34  of FIG. 3, to be installed to operate at the beginning of a timer ISR  29   c  within the timer device driver  29   a.    
         [0097]    A test pattern  112  may format the last few (for example, 10) bytes of a sector write buffer  27   b.  Any known pattern may suffice, for example, a sequential list of all digits from zero to nine may be used. Importantly, the last two digits in such a sequence should be distinct. Thus, a string “0123456789” may provide a test pattern to be written in the last ten bytes of a sector. The test pattern may then be written from a buffer  27   b  to a medium  17  using the BIOS interface for the medium  17  and medium drive  16 .  
         [0098]    Following the test pattern  11   2 , a test  114  may determine whether or not a write error has occurred in writing the buffer  27   b  to the medium  17 . A positive response to the test  114  results in an increment step  116 . The increment  116  tracks the number of successful detections of errors. Thus, the increment  116  indicates that another write error was successfully detected by the FDC  20 . Accordingly, the application  24  may advance from the increment  116  to a test  117 . A test  117  may determine the number of sectors to which the FDC  20  has attempted to write. If the response to the comparison of the test  117  is positive, then all tests are completed and the display step  106  follows. On the contrary, a negative response to this test  117  returns the application  24  to the test pattern  112 , initiating another test cycle.  
         [0099]    A negative response to the test  114  indicates that a write error, known to exist, was undetected by the FDC  20 . Accordingly, a negative response to the test  114  advances the application  24  to a read  118 . The read  118  reads back the last previously written sector, using the BIOS diskette interface, such as the driver  29   b.  The step  118  may then increment the number corresponding to sectors that the FDC  20  has attempted to write.  
         [0100]    The application  24  may next advance to the test  120  to determine whether the last byte that the read step  118  has read back from the written sector to a buffer  27   b  is the last, or the next-to-last element of the test pattern from the test pattern step  112 . That is, for example, in the example above, the test  120  determines whether or not the last byte read back to the buffer  27   b  from this sector being tested is correct (e.g. 9, a value other than 9 indicates that the FDC has failed to write the tenth element of the test pattern into the last byte location of the sector). This indicates that the FDC has not indicated a write error in the test  114 , and yet has produced the error detected by the test  120 . Thus, the last sector written is corrupted.  
         [0101]    A negative response to the test  120  indicates that the last byte was not incorrectly written. Accordingly, the application  24  may advance to the test  117  to determine whether or not the testing is completed. A positive response to the test  120  results in an increment step  122 . The increment step  122  advances the count of undetected errors found during the operation of the FDC  20  during the testing in question. Thus, a step  122  results in a corruption count for sectors attempted to be written by the FDC  20 .  
         [0102]    Referring now to FIG. 7, and also cross-referencing to FIG. 6, the hook step  110  may install a prefix  54  to a timer ISR  29   c  within the timer device driver  29   a  (see FIG. 4). The hook  110  interposes the prefix  124  corresponding to the prefix  54  of FIG. 4, after a call  125  or entry point  125  to the timer ISR  29   c  within the timer device driver  29   a.  Accordingly, whenever the timer ISR  29   c  within the timer device driver  29   a  is called, the prefix  124  will be run before any executables in the timer ISR  29   c  within the timer device driver  29   a.    
         [0103]    The prefix  124  may begin with a read  126  effective to determine a count corresponding to the number of bytes, or a countdown of the remaining bytes, being transferred by the DMA controller  18  from the main memory  14 , through the buffer  27   b  to the FDC  20 . The read  126  may also include a reading of a count (a tick count) of a timer  22  or system clock  22 .  
         [0104]    Following the read  126 , a test  128  may determine whether or not an operation is in process affecting the FDC  20 . The FDC  20  is in operation if a count kept by the DMA controller  18  has decremented (changed) within an elapsed time corresponding to the maximum time required for a byte to be transferred. If no change has occurred during that elapsed time, then one may deduce that no activity is occurring. Accordingly, a negative response to the test  128  results in reexecution of the test  128 . Reexecution of the test  128  may continue until a positive response is obtained. Inasmuch as the application  24  is executing a write during the test pattern  112 , an eventual positive response to the test  128  is assured. In one embodiment of an apparatus and method in accordance with the invention, the first byte transferred may typically be detected.  
         [0105]    A positive response to the test  128  advances the prefix routine  124  to a test  130  to test the countdown or count of the DMA controller  18 . The test  128  corresponds to detection of activity, whereas the test  130  corresponds to iteration of a shadowing process.  
         [0106]    The test  130 , whenever a negative response is received, may advance the prefix routine  124  to the exit  138 .  
         [0107]    On the other hand, a positive response to the test  130  advances the prefix routine  124  to a test  132  effective to evaluate whether or not the countdown is within some selected range at the end of a sector. A negative response to the test  132  indicates that the countdown is not within some desired end-of-sector range, so the prefix routine  124  should exit  138  without waiting longer. That is, interrupts will continue to occur with a frequency that will detect the desired range at the end of the sector being tested.  
         [0108]    A positive response to the test  132  advances the prefix routine  124  to a test  134  for detecting the last byte to be transferred in a sector. If the DMA controller  18  is not counting the last byte to be transferred, then the test  134  may simply continue to test. When the countdown of the DMA controller  18  reaches a value of zero, a positive response to the test  134  advances to a delay step  136 .  
         [0109]    The delay step  136  corresponds to the delay  60  illustrated in FIGS.  4 - 5 . The delay  136  may be implemented by preempting a channel over which the DMA controller  18  is communicating with the FDC  20 . For example, a first channel may be made active by some process, thus, overwriting communication over some channel having lesser priority, and corresponding to the FDC  20 . Likewise, the channel corresponding to the DMA communication with the FDC  20  may be masked (suspended) until the time elapsed for the transfer of the data to the sector has exceeded the maximum time permitted for such transfer. Thus, any and all opportunities for writing the last byte to the sector had expired. Thus, an error condition has been assured. Once the delay  136  has assured an error condition the exit  138  returns control of the processor  12  to the non-interrupted processing state.  
         [0110]    Referring to FIG. 8 specifically and FIGS.  8 - 15  generally, an overview at a high level of abstraction shows an overarching process for implementing a welding process. A process  150  may include a determination  151  of available hardware and support in a computer system. Accordingly a welding process  153  may weld a software layer to a hardware lay such that other software cannot defeat the connection therebetween. In FIGS.  9 A- 9 B,exit messages  182 ,  186  result from failures of tests  156 ,  162 .  
         [0111]    Meanwhile, referring to FIG. 10, a shadowing process  155  may be one form of ISR in the method of FIG. 8, while FIG. 11 illustrates a defense process  157  for eliminating, defeating, or otherwise defending against attempts by other software to unweld a persistent software function  159  (See FIG. 12) from an underlying hardware device or resource. FIGS.  13 - 14  illustrate a check and other command bytes that may result from the method of FIG. 8. FIG. 15 illustrates a method  161  for unwelding the persistent software function, but only by the module responsible for effecting the welding process.  
         [0112]    Referring to FIG. 8 to review in more detail a specific embodiment for implementing a software correction of a hardware state, a process  150  in accordance with the invention may address FDC controllers that are configured to operate with a first-in-first-out (FIFO) architecture. In such an embodiment, a process  152  for loading  152  a driver for a hardware resource (e.g. peripheral device) leads to identifying  154  the processor executing the instructions. Thereafter, a test  156  determines whether or not the processor is a Pentium (P5) type or equivalent, or not. If the device is not, then a do-not-install step  158  is initiated. The step  158  is one of two similar actions.  
         [0113]    By contrast, if the test  156  results in a device that is at least as current, or more current than a P5 architecture, then identifying  160  the floppy diskette controller is useful. The identifying step  160  corresponds to a floppy diskette controller, which may control more than floppy diskette types of media. After identifying  160  the nature of the floppy diskette controller (FDC), a test  162  determines whether or not the FDC operates with FIFO enablement. If not, then a do-not-install step  164  follows.  
         [0114]    Otherwise, for FIFO-enabled FDCs, a save step  166  saves the content from a control register no. 4  (CR 4 ). Next, the bit assigned to the CR 4 .DE location is set  168 . By the setting  168 , the save step  166  is effectively required. Otherwise, the setting step  168  destroys irretrievably the contents of the CR 4 , control register no.  4 , contents.  
         [0115]    A saving step  170  saves to another location the contents of the debug register no.  7  (DR 7 ). The saving step  170  may also save debug register no.  3  (DR 3 ). Saving  172  an original interrupt service routine, associated with a first interrupt, then provides installation  174  of a new or alternative interrupt service routine (ISR).  
         [0116]    In the installing step  174 , a setting step  176  may set the FIFO to an “on” state if executing a solution to the read/write defect of an FDC. The solution represents a curing of the hardware defect of the chip by operating the software solution as described above. Alternatively, setting  178  the FIFO to an “off” state is used for the detection process. The detection process is the determination of whether or not the subject chip has the hardware defect detected and solved by the instant invention.  
         [0117]    Following installation  174 , a setting step  180  sets values of various debug registers in sequence. For example, a global protect may be set, followed by a global use of a Break Point Register no. 3  (BP 3 ). Thereafter, a binary value of 10 may be set for purposes of controlling input and output. Then, a single byte may be set for a length (LEN 3 ). Finally, an input and output port may be set using the debug register (DR 3 ). Thereafter, the process  150  may return  181 .  
         [0118]    Referring to FIG. 9A (e.g. see FIGS. 9A and 9B), the details of the do-not-install step  158  are straightforward. An output step  182  provides a message or indication that the processor does not support the current driver. A lack of support causes an exit. Accordingly, the process  150  is not completed otherwise.  
         [0119]    Referring to FIG. 9B, the do-not-install step  164  provides a different output  186 . The output includes a message, warning, signal, or the like indicating that the subject FDC does not support a FIFO architecture. Accordingly, the driver must exit  188 . Thus, the process  150  terminates.  
         [0120]    Referring to FIG. 10, an interrupt service routine (ISR)  190  may be thought of as a breakpoint ISR  190 . Accordingly, a test  192  determines whether the debug register  6  has bit BD set. If so, then debug register access  194  occurs. Otherwise, a test  196  determines whether the debug register  6  has bit B 3  set. If so, then an FDC command  198  occurs. Otherwise, then the invocation  199  follows, for invoking  200  the original interrupt service routine.  
         [0121]    Referring to FIG. 11, the details of the debug routine access  194  begin with obtaining  202  a next instruction to be executed by the processor. The address for the instruction is located in the CS:EIP register pair.  
         [0122]    Thereafter, a test  204  determines whether the next instruction contains a first byte value designated by the test  204 . For example, the testing value may be 0×0F. This value corresponds to 00001111 in binary. If the test  204  is negative, then invocation  199  occurs. Otherwise, the test  206  determines whether or not the second byte has a test value. In one embodiment, the test value is 0×23. This corresponds to a binary value of 00100011, which indicated an attempt to write to one of the debug registers.  
         [0123]    Again, if a test  206  results in a negative response, then invocation  199  is appropriate. Otherwise, a test  208  directed to the third byte anded with 0×38 determines whether the value is 0×18. This process effectively takes the form of 11 ee errr indicating that debug register  3  is the target register. If the response to the test  208  is positive, then the incrementing step  210  follows. The incrementing step  210  increments past the next instruction, thus, repelling an attempt to modify DR 3  (unweld). The value of the register EIP plus 3 is loaded into the register EIP because the instruction is three bytes long.  
         [0124]    If the results of the test  208  are negative, then a test  212  determines whether or not the third byte anded with 0×38 has a value of 0×38. If not, then the invocation  199  occurs again. However, a positive result to the test  212  means that a debug register  7  (DR 7 ) is the target register. Thereafter, the incrementing step  210  proceeds as described above. Following the incrementing step  210 , a return  214  from the interrupt returns the processing to its previous state.  
         [0125]    Referring to FIG. 12, an FDC command  198  proceeds with a test to determine whether this is a new FDC command. If not, then more command bytes  218  may follow. Otherwise, a positive response engages another test  220  determining whether a configure command flag is set. If not, then an analysis of the command  222  follows.  
         [0126]    Otherwise, a positive response leads to an issuing step  224  to issue a configure command. This configure command turns on or enables the FIFO. The issuing step  224  may include turning  226  or activating  226  the FIFO to a state of “on” if the solution process is the subject of interest. If, on the other hand, detection of the presence of the error solved by the invention is the issue, then the FIFO maybe turned off  228 . Turning the FIFO off  228  is important for providing the timing required in order to properly detect the presence of the design flaw in the hardware.  
         [0127]    Thereafter, a resetting step  230  resets the configure command flag, after which a return  232  returns control of the system from the interrupt.  
         [0128]    Referring to FIG. 14, a check command step  222 , may begin with a test  234  to determine whether the command flag is set to configure. If not, a return  232  may return control from the interrupt. If, on the other hand, the test  234  returns a positive result, then setting  236  the configure command flag may precede a return  232  from the interrupt. Referring to FIG. 14, if more command bytes  218  are indicated as a result of the test  216  of FIG. 12, then a return  232  from the interrupt occurs directly.  
         [0129]    Referring to FIG. 15, unloading  238  a driver, begins by restoring  240  the original interrupt service routine (ISR). Then, the values are restored  242  into the debug register  3  (DR 3 ), the debug register  7  (DR 7 ) returning these registers to their original state. Thereafter, restoring the original values to the control register  4  (CR 4 ) completes the restoration of the state of the machine. Accordingly, a return  246  can follow immediately.  
         [0130]    The invention described heretofore provides a detection solution that may be completely implemented in software as a device driver  29   b  that is capable of detecting defective FDCs  20  without visual inspection and identification of the FDCs. Furthermore, the unique and innovative approach taken, allows the implementation of the invention to accurately and correctly detect defective FDCs even when non-defective old-model FDCs are involved. Simply stated, it is not sufficient to determine whether the FDC under test is an old or new model FDC. Various vendors manufactured old-model FDCs that are not defective. Therefore, a two-phase detection process may correctly determine whether or not the FDC under test is defective.  
         [0131]    The number of FDCs installed in computer systems today is well over 100 million. In order to identify defective FDCs, vendors and consumers that have defective FDCs  20  installed have very few alternatives (e.g. recalls; replacement), of which most are extremely costly, for determining whether or not their systems are susceptible to the data corruption presented by defective FDCs  20 . Therefore, an apparatus and method that may be implemented as a software-only solution to this problem is a significant advance in the computer industry. Moreover, the robust design allows the apparatus and method of the present invention to address processor speeds that encompass the original IBM Personal Computers executing at 4.77 MHZ to the latest workstations that execute at well over 1 GHZ.  
         [0132]    The function of transfer of data to devices controlled by the FDC is described above in one embodiment as occurring through direct memory access (DMA). Nevertheless, this function may be accomplished with any suitable memory controller or other manner of data transfer. For example, one manner disclosed above involving a memory controller other than a DMA includes programmed input and output (I/O) accomplished directly by the microprocessor. Thus, in this instance, one skilled in the art will understand that in the discussion above, where a DMA is used, programmed I/O or other types of memory controllers may be readily substituted.  
         [0133]    A further aspect of the present invention involves specific implementations of a method for detecting and preventing floppy diskette controller data transfer errors in computer systems. One embodiment of the method has been included by incorporating by reference U.S. Pat. No. 5,379,414 issued to Phillip M. Adams on Jan. 3, 1995. Another embodiment of the method has been included by incoprorating by reference U.S. Pat. No. 5,983,002  
         [0134]    One such specific implementation involves substituting a magnetic tape back-up device or an optical device, or other such peripheral, non-volatile memory device for the floppy drive previously described in the specific embodiment of the method. In so doing, the method substantially as disclosed is employed, substituting the use of the alternate peripheral, non-volatile memory device for the floppy drive. Appropriate commands are also substituted, as would be readily apparent to one skilled in the pertinent art.  
         [0135]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Technology Classification (CPC): 6