WO1998029807A1

WO1998029807A1 - Real time services in backwardly compatible operating systems

Info

Publication number: WO1998029807A1
Application number: PCT/US1997/023907
Authority: WO
Inventors: Richard Tarquini
Original assignee: Cirrus Logic, Inc.
Priority date: 1996-12-30
Filing date: 1997-12-24
Publication date: 1998-07-09
Also published as: KR20000062377A; EP0948769A1; TW405091B; JP2001507835A

Abstract

The problems associated with CPU hoggin when running legacy applications, such as DOS applications, on a modern operating system, such as Windows 95, are overcome by creating a Virtual Device Driver VxD to manage needs for guaranteed CPU access by various processes and devices. The virtual device driver utilizes services of Virtual Machine Manager to guarantee CPU access by requesting processes and devices.

Description

REAL TIME SERVICES IN BACKWARDLY COMPATIBLE OPERATING SYSTEMS

FIELD OF THE INVENTION This invention relates to multitasking computer systems and methods, and, more particularly, to techniques for ensuring adequate CPU resources to a real time application serviced by an operating system which is backwardly compatible to permit the execution of DOS applications.

BACKGROUND OF THE INVENTION Newly designed microprocessors may include enlarged memory addressing facilities and revised architecture which result in enhanced capabilities. When such microprocessors are used in new computer systems, they often produce computers which are functionally superior to their predecessors due to these enhanced capabilities. Despite any functional advantages a new computer may have over its predecessors, a computer employing an improved microprocessor may not be a commercial success. Computer programs, sometimes referred to as "software," are microprocessor specific. Therefore, when a computer employing a new microprocessor is introduced into the marketplace, there is generally little or no software which can run on it. Existing software, written for previous microprocessors, is likely incompatible with the new computer. As a result, sales of such new computers will often be sluggish until consumers see that adequate software is available for the computer. Additionally, consumers with libraries of software for existing computers may be reluctant to purchase new computers which would require them to invest in all new software. This problem is often compounded by the fact that software writers and publishers are reluctant to produce software for a new microprocessor until sales of computers incorporating the microprocessor are sufficient to create a relatively large group of potential purchasers of the software. This "wait and see" attitude on the part of both consumers and software writers can jeopardize the success of a new microprocessor and computers using the microprocessor. Designers of new microprocessors sometimes attempt to solve this problem by designing a new microprocessor such that it will operate in multiple modes. In a first mode, for example, the microprocessor will emulate a prior microprocessor and run existing programs written for the prior microprocessor. In a second mode, the microprocessor will make full use of its enhanced capabilities. Such a design will enable manufacturers of computer systems using the microprocessor to advertise that the entire body of existing programs written for the prior microprocessor will run on their computer, thereby (in theory) stimulating computer sales to a point where software writers will begin to write programs designed to run in the new enhanced mode .

One such microprocessor is the Intel 80286, which ia manufactured by the Intel Corporation of Santa Clara, California. The design and operation of the Intel 80286 is described in detail in a publication entitled "iAPX286 Programmer's Reference Manual Including the iAPX286 Numeric Supplement," which is available from the Intel Corporation and is hereby incorporated by reference. The Intel 80286 (hereinafter "80286") operates in two modes. In a first mode, called the "real mode," the 80286 emulates the architecture of Intel's previous 8086, 8088 microprocessor family, which is used in the IBM PC and compatible computers, for example. Thus, computer which incorporate the 80286 microprocessor, such as the IBM PC/AT, can run existing 8086 programs written for the IBM PC and compatible computers.

In a second mode, called the "protected mode," the 80286 architecture provides enlarged memory addressing capability, enhanced multitasking support features, and a sophisticated protection scheme.

Another such microprocessor is the Intel 80386. The design and operation of the Intel 80386 is described in detail in a publication entitled "iAPX386 Programmer's Reference Manual Including the iAPX386 Numeric Supplement", which is available from the Intel Corporation and is hereby incorporated by reference.

The 80386, in addition to a real and protected mode as described above for the 80286, has a third mode, called virtual-8086 mode. In virtual 8086 the 80386 emulates the 8086 processor in a manner similar to the real mode. The distinction between real and virtual-8086 mode is that in virtual-8086 mode the 80386 provides memory-management, protection, and multitasking support. The virtual-8086 mode allows 8086 programs to execute as a task on the 80386. Each task in virtual-8086 mode has the illusion that it is executing on a 8086.

A virtual machine monitor (VMM) , which is special operating-system software, coordinates the multitasking of several 8086 programs. The VMM executes in protected mode. There are two standard techniques for transferring control from a task to a VMM so that another task can be started. First, the VMM configures to 80386 so that all interrupts, software and hardware, that are executed by an 8086 program cause control to be transferred to the VMM. Second, the VMM sets a timer interrupt. When interrupted after the specified interval, the A/MM receives control.

These techniques can be used to support the transfer from 8086 program that are designed to execute under a disk operating system (DOS) . A typical personal computer DOS, such as MS-DOS Version 3.X offered by Microsoft Corporation of Redmond, Washington, is a single-threaded operating system; that is, DOS is not designed to support a multitasking environment. When DOS is executed in a multitasking environment, problems can occur when DOS is interrupted. If DOS is randomly interrupted during the execution of a function, such as during execution of an interval timer, then the transfer to another task can cause the DOS data structures to be corrupted. Consequently, a A/MM will allow DOS to complete a function before another task is started. Upon exit from a DOS system call, the DOS data structures are in an appropriate state.

Unfortunately, a A/MM that allows all functions calls to complete before transferring tasks will result in poor system performance. Several system calls of DOS may take an indefinite amount of time to complete. For example, a call to retrieve a character from the keyboard will not complete until a key is actually entered. Similarly, if a program issues a system call to read from a communication port, the system call will not complete until a character is actually received. The DOS loops through a section of code checking the port to see if the character has been received. Consequently, no other task can be scheduled for this indefinite period of time.

A timer interrupt of system calls of indefinite duration is insufficient because the A/MM does not know whether the DOS was in a state where the data structures were non-corruptible.

U.S. Patent No. 4,974,159 to Hargrove et al . which issued on November 27, 1990 addresses the problem of DOS routines failing to transfer control to a virtual machine manager (A/MM) by writing a virtual machine breakpoint instruction into the executable code to ensure that control will transfer to the virtual machine manager periodically so the system will not lock up by virtue of the DOS application. In Hargrove's approach, certain points in program execution are detected where a task switch can occur without corrupting the DOS data structures. Certain of these points are selected for the insertion of a virtual machine breakpoint . When the breakpoint is reached in execution, the virtual machine manager is then free to start another task or perform other functions without corrupting the DOS data structures. The breakpoint locations used for insertion of a virtual machine breakpoint by Hargrove are located in DOS system calls of indefinite duration, such calls to read a keyboard call. If no key is pressed, then the application will hold until a key is pressed. Hargrove provides no examples of placing virtual machine breakpoints at any other type of location.

The implementation of Hargrove's technique requires that a copy of the selected routine be separately stored to recover portions of the code overwritten by the one byte virtual machine breakpoint instruction in the executable code. This is complicated and requires unnecessary process steps and storage.

The Windows95 operating system is an operating system of the type described above which is subject to CPU hogging by a DOS application running in a virtual machine environment . The Intel Architecture Signal Processing

Operating System (IASPOX) introduce the concept of native signal processing (NSP) and was developed by Intel and Spectron Microsystems.

The IASPOX operating system brings along with it significant overhead in regard to system memory and CPU usage and utilization. IASPOX must be purchased and installed separately on the host computer. IASPOX takes over the PC's scheduling of tasks and only runs windows applications/drivers when IASPOX applications are idle. IASPOX reprograms the real-time clock to approximately 900 microsecond granularity, incurring significant interrupt (15 μSec per interrupt on 486/66Mhz in protected mode) overhead even if no IASPOX tasks are running. Rounded down to 1000 interrupts per/second or once every millisecond and the interrupt latency alone would consume 1.5% of CPU without executing any code.

Currently IASPOX is not endorsed by Microsoft since it does not follow the VxD programming model and undermines the Window 95 kernel. Approximately 80% of the current IASPOX code is already in Windows95, leading to redundant interfaces and needless memory consumption. It also requires programmers to lean a new kernel and associated primitives, tools and development environment (15MB of disk space) .

In addition, IASPOX apparently runs as a super operating system with Windows95 operating as a task thereunder. In this way, IASPOX maintains control over access to the processor, regardless of the Windows95 state.

SUMMARY OF THE INVENTION

In accordance with the invention, real time applications can be guaranteed CPU access regardless of the state of any applications, including DOS applications concurrently running. In accordance with the invention, nested execution/priority event mechanisms provided by a virtual machine manager are utilized to provide that access. The invention is implemented as a process, called Real Time Services or RTS . RTS is implemented as a Virtual Device Driver (VxD) which schedules a priority call back function to be run, regardless of which application or virtual machine is executing. The invention relates to methods and apparatus for scheduling a repetitive process in a computer by running a scheduling process which interacts with the operating system and at least one process or device to ensure CPU access regardless of the state of any application running on the computer.

Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a representation of an exemplary prior art operating system useful for carrying on the invention.

Figure 2 is a block diagram of components of an exemplary device driver for the operating system shown in Figure 1.

Figure 3 is a block diagram illustrating how real time services (RTS) are implemented as a virtual device driver in accordance with the invention. Figure 4 is a block diagram of a host based modem using real time services in accordance with the invention to ensure adequate CPU access from modem functions .

Figure 5 is a timing representation illustrating interprocess communications between RTS and the modem VxD and operating systems services supported by the virtual machine manager and a virtual device driver for a timing device (VTD) .

Figure 6 is a timing representation of interprocess communications used periodically to activate a modem's BACKGROUND function.

Figure 7 is a timing representation of interprocess communications used to act as a heartbeat for the modem. Figure 8 is a timing representation of inter process communication used to permit an application to initiate a transfer at a time which will not interfere with other processes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 is a representation of an exemplary prior art operating system useful for carrying out the invention.

The application layer 100 includes a variety of applications including 32 bit applications as well as 16 bit applications and DOS applications. Shell 110 acts an interface to operating system core features.

It also includes a plurality of user interface tools.

The core is composed of three comments - a user area, a kernel area, and a graphical device interface. The User component manages input from the keyboard, mouse, and other input devices and output to the user interface (windows, icons, menus, and so on) . It also manages interaction with sound driver, timer, and communications ports. The Operating System described in Figure 1, preferably Windows95, uses an asynchronous input model for all input to the system and applications. As the various input devices generate interrupts, the interrupt handler converts these interrupts to messages and sends the messages to a raw input thread area, which in turn passes each message to the appropriate message queue. Although each 32 bit -based thread can have its own message queue, all 16 bit- based applications share a common message queue. The Graphical Device Interface (GDI) is the graphical system that manages what appears on the screen. It also provides graphics support for printers and other output devices. It draws graphic primitives, manipulates bitmaps, and interacts with device-independent graphic drivers, including those for display and printer output device drivers.

The Kernel provides base operating system functionality including file I/O services, virtual memory management and task scheduling. Exception handling is another service of the

Kernel. The Kernel also allocates virtual memory, resolves import references, and supports demand paging for the application. The Kernel provides services to both 16-bit and 32-bit applications. The central information database in the operating system is called the Registry. This hierarchical database both simplifies the operating system and makes it more adaptable.

A primary role of the Registry in the operating system is to serve as a central repository for hardware-specific information for use by the hardware detection and Plug and Play system components. The operating system maintains information about hardware components and devices that have been identified through an enumeration process in the hierarchical structure of the Registry. When new devices are installed, the system checks the existing configuration in the Registry to determine the hardware resources (for example, IRQs, I/O addressees, DMA channels, and so on) that re not being used, so the new device can be properly configured without conflicting with a device already installed in the system.

Just as the Configuration Manager provides for all resources needed by each device on the computer, another component, the Virtual Machine Manager, provides for resources needed for each application and system process running on the computer. The Virtual Machine Manager creates and maintains the virtual machine environments in which applications and system processes run.

A virtual machine (VM) is an environment in memory that, from the application's perspective, looks as if it is a separate computer, complete with all of the resources Machine Manager provides each application with the system resources it needs.

The operating system has a single A/M called the

System A/M, in which all system processes run. In addition, all 32 bit-based and 16 bit-based applications run in this A/M. Each MS-DOS-based application runs in its own AM.

The Process Scheduler is the component responsible for providing system resources to the applications and other processes you run, and for scheduling processes to allow multiple applications to run concurrently.

The Process Scheduler also schedules processes in a way that allows multiple applications and other processes to run concurrently. The operating system uses two methods for concurrent process scheduling - cooperative multitasking and preemptive multitasking.

In earlier operating systems such as Windows 3.1, applications run concurrently through a method known as coopera tive mul ti tasking. Using this method, the operating system required an application to check a message queue periodically and to relinquish control of the system to other running applications. Applications that did not check the message queue frequently would effectively "hog" CPU time and prevent the user from switching to another application. For compatibility reasons, the operating system cooperatively multitasks 16 bit-based applications.

The operating system uses preemptive mul ti tasking for 32 bit-based applications. This means that the operating system takes control away from or gives control to another running task, depending on the needs of the system.

Unlike 16 bit-based applications, 32 bit-based applications do not need to yield to other running tasks to multitask properly. 32 bit-based applications can take advantage of mul ti threading, a mechanism that the operating system provides to facilitate the ability to run applications concurrently. A 32 bit -based application running in the system is called a process in terms of the operating system. Each process consists of at least a single thread of execution that identifies the code path flow as it is run by the operating system. A thread is a unit of code that can get a time slice from the operating system to run concurrently with other units of code, and must be associated with a process. However, a 32 bit-based application can initiate multiple threads for a given process to enhance the application for the user by improving throughput, enhancing responsiveness, and aiding background processing. Because of the preemptive multitasking nature of the operating system, threads of execution allow code to be smoothly processed in the background.

The IFS Manager arbitrates access to file system devices, and other file system device components. To support Plug and Play functionality, the operating system architecture includes a Configuration Manager, which orchestrates the configuration process . This process might involve many bus and device architectures coexisting on a single system, with more than one device type using the same bus architecture, yet with each device having a separate set of configuration requirements. (A bus is the mechanism that allows information to be transferred between the computer and the device.) For example, a mouse and a keyboard can both use the same keyboard controller bus; a CD-ROM drive and a hard disk drive might both use the same SCSI bus.

Configuration Manager works with a number of subcomponents to identify each bus and each device on the system, and to identify the configuration settings for each device. Configuration Manager ensures that each device on the computer can use an IRQ, I/O port addresses, and other resources without conflict with other devices .

Configuration Manager also helps monitor the computer for changes in the number and type of devices present and manages the reconfiguration of the devices, as needed, when changes take place. As these events occur, Configuration Manager communicates the information to applications.

To perform its role, Configuration Manager calls on the bus enumerators to identify all the devices on their specific buses and their respective resource requirements .

The operating system provides improved support for hardware devices and peripherals including disk devices, display adapters, mice and other pointing devices, modems, fax machines, and printers.

In previous operating systems, such as Windows 3.1, device drivers were, for the most part, monolithic and complex to develop. The operating system being described uses a universal driver/mini- driver architecture that makes it easier for hardware vendors to provide device-specific code for their hardware .

As shown in Figure 2, a universal driver (210) includes most of the code necessary for devices in a particular class of devices (such as printers or modems) to communicate with the appropriate operating system components (such as the printing or communications subsystems) . A mini-driver (220) is the relatively small and simple driver than contains any additional instructions needed by a specific device. In many cases, however, the universal driver for a particular category of devices also includes the code needed to operate devices designed to the most common standard for that category. (For example, the Unimodem driver works with all modems supporting AT commands . )

A v i r t u a l d e v i c e d r i v e r

(VxD) is a 32-bit, protected-mode driver that manages a system resource, such as a hardware device or installed software, so that more than one application can use the resource at the same time. VxD refers to a general virtual device driver - the x represents the type of device driver. For example, a virtual device driver for a display device is known as a VDD, a virtual device driver for a timer device is a VTD, a virtual device driver for a printer device is a VPD, and so forth.

In previous operating systems, such as Windows 3.1, VxDs were statically loaded and took up a lot of memory space. However, the operating system being described dynamically loads VxDs - that is, only those that are needed at any given time are loaded into memory. In addition, the new VxDs don't require all of their memory to be page-locked, thereby further increasing the available memory in the system.

VxDs support all hardware devices for a typical computer, including disk controllers, serial and parallel ports, keyboard and display devices, and so on. If the state of the hardware device can be disrupted by switching between multiple applications, the device must have a corresponding virtual device for each application which ensures that the device is in the correct state whenever an application continues .

Although most virtual devices manage hardware, some manage only installed software, such as an MS-DOS device driver or a TSR program. Such virtual devices contain code to emulate the software or ensure that the software uses data that applies only to the currently running application. Also, VxDs are often used to improve software performance . Figure 3 is a block diagram illustrating how real time services (RTS) are implemented as a virtual device driver in accordance with the invention. As shown in Figure 3, at the ring three level, the system virtual machine runs a plurality of 32 bit applications in a separate address space. However, 16 bit applications are run in a single address space. In addition, DOS applications run as separate virtual machines as indicated. The virtual machine manager subsystem is shown at ring zero. In addition to other functions, it manages virtual device drivers including the real time services of the invention. Real time services, being implemented as a virtual device driver, has access to certain virtual memory managers subsystem capabilities necessary to ensure CPU access to real time services when that is needed. This is explained more hereinafter.

Figure 4 is a block diagram of a host based modem using real time services in accordance with the invention to ensure adequate CPU access for modem functions. The software architecture of the application being described is partitioned into a plurality of layers for convenience of description. At the application layer 400, 32 bit applications such as Window application 401 and DOS applications, such as application 402 may be running simultaneously. In layer 410, the virtual machine manager 413 is illustrated together with the configuration manager 412. These were discussed. VCOMM block 411 is a communications device driver that provides the protected mode services that allow windows based applications and drivers to use ports and modems. To conserve system resources, communications drivers are loaded into memory only when in use by applications. Also, VCOMM uses Plug and Play services in the operating system to assist with configuration and installation of communications devices. Real time services block 414 is shown partially within layer 410 and partially within layer 420. The heavy line 480 is designed to symbolize the boundary between the operating system and the software for the host based modem of this particular example. The boundary line is not meant to represent a fixed boundary but rather to indicate that from application to application, more or less of the code may be implemented either in the operating system side or the modem side of the software stack. The fact that RTS crosses the boundary 480 is merely indicative of the fact that RTS serves as an interface to the virtual machine manager 413 for modem services.

As shown in Figure 3, 16 bit applications run in a single address space. They are cooperatively scheduled, rather than preemptively scheduled. The 32 bit applications shown as operating in a single separate address space are preemptively scheduled and therefore get CPU attention when needed. However, the 16 bit applications perform scheduling using a message board. Thus, when a 16 bit application has control of the processor, it retains control until its posts a message for relinquishing control. If such an application is uncooperative, it can hog the CPU to the exclusion of other processes that need attention. In the past, a modem has utilized a microcontroller and a data pump. It would be desirable to eliminate the micro controller and have the processing that would otherwise have been done by the microcontroller be done by the host. However, such a host based modem would need guaranteed access to the CPU in order to meet sometimes stringent requirements for events and responses. The ability of a 16 bit application to be uncooperative or of other applications to require dedicated access to the CPU in derogation of other claims creates a possibility that it would be impossible to create a host based modem unless one could guarantee access to the CPU within the required specified intervals. In accordance with the invention, the services of the VxD architecture are utilized to allow modem to get a slice of CPU time regardless of what other applications or drivers might be running.

The ACU background process or function is roughly analogous to a main routine and calls a plurality of subordinate routines sequentially. In a microcontroller environment, the ACU background loop would run continuously and be handled by the microcontroller. With the microcontroller functionality being handled by the host, in a host based modem environment, one needs to ensure that sufficient CPU access and time exist to permit modem functions to reliably occur without, for example, dropping any connections or characters.

The windows interface layer 420 includes port driver interface 421, DOS COMM port virtualization 422 and plug and play interface 423. These modules permit the applications of layer 400 to access, through the operating system, the main code for the modem. Each of the interfaces of the windows interface layer, communicate with a universally synchronous receiver transmitter (UART) emulation module 431. This, too, permits each of the interface modules of the interface layer to have a standard interface to the code below. The module layer, 440, includes a fax module 441, a data module 442 (V.42) a voice module (VCE) (443) and a DTE module 445. Modules 441 - 443 handle the data for the respective types of services. ACU, referred to above, stands for Automatic Control Unit and serves to configure the modem. ACU operates as a background process which repetitively calls all subordinate routines sequentially. If a particular module 442 has work to do, it will hold the background process while its work is completed before passing control to the next module listed in the loop. As discussed above, if the ACU module does not get activated frequently enough, characters or connections may be lost for the various services . The DTE module 445 of layer 440 manages moves of I/O buffer information to the respective modules. Module I/O layer 450 contains respective interfaces for the various types of service modules 441 - 443 together with a modem task 454. Modem task 454 provides a standardized interface to the modules within its layer and above insulating them from the peculiarities of the data pump 472. The interrupt layer includes a data transmit/receive module 461 which moves characters from the data pump through the PCI/0 interface 471 to the service I/O modules 451 - 453 and then to corresponding modules 441 and 443. It is particularly important that the interrupt layer timely service the data pump to ensure that no characters are lost as result of buffer overflow or the like. Timer 462 helps do that. The timer is periodically activated by RTS 414 to ensure a sufficiently frequent heartbeat to the modem. Figure 5 is a timing representation illustrating interprocess communications between RTS and the modem VxD and operating system services supported by the virtual machine manager and a virtual device driver for a timing device (VTD) . This particular drawing includes several services running simultaneously. To facilitate explanation of each of the types of services running, portions of this drawing will be extracted and displayed in subsequent figures. Three principal services are being illustrated simultaneously in Figure 5. The first is the background call back which activates the ACU in the modem in a timely fashion to ensure adequacy of modem functions. The second service is one designed to ensure a frequent heartbeat for the modem. The third service permits an application process to initiate a transfer at a time which will not interfere with other processes. These are shown respectively in Figures 6 - 8. In Figure 6, the process begins with a request from the modem device driver to RTS to register a background call back. In response thereto, RTS invokes the set_global_timeout command to the virtual machine manager. RTS also sends a VTD_begin_min_int Period to set the granularity of the timer. Typically, the timer is set at a default of 54 milliseconds. However, it may be reduced, using this command, to as small as the granularity of a programmable interrupt timer (PIT) allows, such as an Intel 8253 timer. The modem VxD then sets a background timeout interval . Typically, this is a hundred milliseconds or less. In response to the global timeout set previously, the global timeout occurs and the VMM module notifies RTS. RTS then sends a schedule_global_event command to the VMM and receives a global event scheduled response . When that response comes in, a background call to ACU is executed and another set global_timeout command is sent to the A/MM. The last four interchanges between the RTS and the A/MM constitute a repetitive set which occur periodically, resulting in execution of the ACU background process periodically.

Figure 7 is a timing representation of interprocess communications used to act as a heartbeat for the modem. The modem VxD registers a timer call back with RTS and sets the timer time out interval. In response thereto, RTS sends a set_async_timer to the VMM and, when that timer times out, RTS is notified by A/MM and executes a timer call back which triggers a heartbeat or a decrement of the modem clock in the modem code. After the timer call back is executed, RTS again sends a set_async_timer command to the A/MM. The process of setting an asynchronous timer, having the timer time out and executing a timer call back as a heartbeat are repeated periodically to ensure an adequate heartbeat for the modem. Figure 8 is a timing representation of interprocess communication used to permit an application in layer 400 to initiate a transfer at a time which will not interfere with other processes. In certain initialization sequences, a windows application may request information about the "personality" of a modem. Such a call would be routed to RTS which would then invoke a SHELL CallAt

AppyTime . When the A/MM detects that the personality exchange between the modem and the application can occur without damaging ongoing I/O or other processes, an application call back will be executed to the application and the exchange will occur.

Thus, by using real time services, and the services of the virtual machine manager, a host based modem or other process or device can be implemented which is guaranteed to receive an adequate share of CPU attention regardless of the other applications or drivers running simultaneously. By implementing this real time service as a virtual device driver, one has access to the services of the virtual machine manager in a way which permits fair and equal competition for CPU time regardless of the problems that would otherwise occur in the prior art .

In this disclosure, there is shown and described only the preferred embodiment of the invention, but, as aforementioned, it is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

Claims

WHAT IS CLAIMED IS:

1. Apparatus for ensuring adequate computer resources to processes or devices, comprising; a. a computer; b. an operating system operation on said computer which is backwardly compatible to run DOS applications, and c. a virtual device driver, interacting with said operating system and at least one process or device, to ensure CPU access regardless of the state of any DOS application.

2. Apparatus of claim 1 in which said operating system is Windows95.

3. Apparatus of claim 1 in which said virtual device driver interacts with a Virtual Machine Manager.

4. Apparatus of claim 1 in which the at least one process or device is a host based modem.

5. Apparatus of claim 4 in which said virtual device driver is used to schedule a recurring background process .

6. Apparatus of claim 4 in which said virtual device driver is used to schedule a recurring heartbeat process .

7. Apparatus of claim 4 in which said virtual device driver is used to schedule an exchange of modem information between an application and a modem.

8. Apparatus of claim 1 in which the at least one process or device is a device external to said computer .

9. Apparatus of claim 1 in which the at least one process or device is a device for collecting real time data .

10. A method for scheduling a repetitive process in a computer having an operating system which is backwardly compatible to run DOS applications, comprising the step of: a. running a scheduling process which interacts with the operating system and at least one process or device to ensure. CPU access regardless of the state of any DOS application.

11. A method for scheduling a repetitive process on a computer having an operating system having a Virtual Machine Manager and a timing process, comprising the steps of : a. running a virtual device driver to serve as a scheduling mechanism for repetitive processes using services of said Virtual Machine Manager.

12. The method of claim 12 in which said services of said Virtual Machine Manager include set global timeout .

13. The method of claim 12 in which said services of said Virtual Machine Manager include schedule global event .

14. The method of claim 12 in which said services of said Virtual Machine Manager include set async timer.

15. The method of claim 12 in which said services of said Virtual Machine Manager include a shell call at Appy time.

16. A system for servicing real time requirements, comprising : a. a computer including an operating system, b. one or more peripheral devices managed by at least one peripheral device driver; c. a process scheduler, implemented as a virtual device driver, for ensuring access to computer resources by at least one of said peripheral devices .

17. The system of claim 16 in which one of said one or more peripheral devices is a network control board.

18. The system of claim 17 in which said network control board is connected to a network to which one or more user devices are connected.

19. A method of servicing real time requirements of peripheral devices comprising the steps of : a. using a virtual device driver to act as a common scheduling mechanism for processes related to said peripheral devices which require regular and guaranteed access to computer resources .

20. A computer program product comprising: a. a memory medium; and b. a computer program stored on said memory medium, said computer program comprising instructions for running a scheduling process which interacts with an operating system and at least one process or device to ensure CPU access by said process or device regardless of the state of any DOS application.

21. A computer program product for scheduling a repetitive process on a computer having an operating system having a Virtual Machine Manager and a timing process comprising: a. a memory medium; b. a computer program stored on said memory medium, said computer program comprising instructions for running a virtual device driver for to serve as a scheduling mechanism for repetitive processes using services of said Virtual Machine Manager.