System, Method and Program for Controlling Access to an Input/Output Device Possible Resource Settings Data in an Advanced Configuration and Power Interface Operating System

The invention relates to protecting configuration data associated with input-output (I/O) devices.

Known device configuration techniques such as plug-and-play are implemented via basic input-output system (BIOS) instructions stored in read only memory (ROM). One responsibility of a plug-and-play BIOS is to initialize all plug-and-play compatible devices coupled to a computer system's motherboard (main circuit board) during start-up. One aspect of this responsibility is the allocation and assignment of system level resources such as direct memory access (DMA) channels, interrupt request lines (IRQs), I/O addresses, and memory addresses.

A plug-and-play device can have two types of resource settings: current resource settings (CRS) and possible resource settings (PRS). Current resource settings refer to actual resource values (e.g., IRQ 4) and reflect the physical configuration of a device. Possible resource settings refer to those resource values that a device may be assigned (e.g., any IRQ between 3 and 9).

If a plug-and-play device has more than one PRS, known device configuration techniques allow a user to change resource assignments. Resource modification is generally performed during system start-up by an application that is executed before control is passed to an operating system (i.e., before the operating system is loaded). If a computer system's resources are locked, the user will be prompted for a password before any resource assignment changes can be made.

Under the new advanced configuration and power interface (ACPI), information associated with motherboard plug-and-play devices is stored in ACPI tables. This information, which is available to the operating system at all times, can include for each device: (1) a control method for determining the device's current configuration, i.e., CRS; (2) a list of possible resource values, i.e., PRS; and (3) control methods for modifying the device's resource values. Under the ACPI specification, there is no provision to reject (i.e., lock) a request to modify plug-and-play resources. If an ACPI operating system has data reflecting a device's PRS, the system may modify those settings.

In one aspect, the invention features a method to control access to configuration data associated with a device in a computer system, where the configuration data is normally accessible to the computer's operating system when loaded at an expected memory location. The method includes determining if access to the configuration data is to be blocked and, if so, not making the configuration data accessible at the expected memory location. In some embodiments, the configuration data includes possible configuration setting information for a motherboard plug-and-play device. In other embodiments, the computer system executes an advanced configuration and control interface (ACPI) operating system, and the expected memory location is defined by one or more ACPI tables.

In another aspect, the invention features a program storage device having instructions encoded therein to perform the inventive method. In yet another aspect, the invention features a computer system capable of controlling access to device configuration data.

FIG. 1 shows a computer system.

FIG. 2 shows a system read only memory.

FIG. 3 shows an advanced configuration and power interface computer system start-up procedure.

FIG. 4 shows a nonvolatile random access memory.

FIG. 5 shows loading device resource information from read only memory to random access memory during computer system start-up.

Referring to FIG. 1, an advanced configuration and power interface (ACPI) computer system 100 providing plug-and-play device configuration security includes host processor (CPU) 102, random access memory (RAM) 104, read only memory (ROM) 106, nonvolatile random access memory (NVRAM) 108, and one or more plug-and-play devices 110 (only one shown) coupled to system bus 112. Illustrative host processors 102 include the PENTIUM, PENTIUM PRO, PENTIUM-II, and 80X86 families of processors from Intel Corporation. As shown in FIG. 2, system ROM 106 generally provides storage for computer system 100's basic input-output system (BIOS) instructions 200, ACPI table data 204, and system input-output device configuration information 206. System ROM 106 can be embodied in programmable versions of read only memory such as electrically erasable programmable ROM (EEPROM). System ROM 106, NVRAM 108, and plug-and-play device 110 will be discussed more fully below.

Referring again to FIG. 1, bridge circuit 114 couples system bus 112 to secondary bus 116. Components coupled to secondary bus 116 include input-output (I/O) control circuit 118, video controller 120 and associated display 122, disk controller 124 and associated disks (one shown) 126, and one or more expansion slots 128. Input-output control circuit 118 can provide an interface for devices such as user keyboard 130, pointer device 132, and serial 134 and parallel 136 ports.

Referring to FIG. 3, computer system 100 start-up (also referred to as power-on self test or POST processing) begins with system BIOS execution at step 300. If a user does not attempt to modify the current resource setting (CRS) of motherboard plug-and-play device 110 (the `no` prong of step 302), a test is made to determine if system resource settings have been locked (step 304). As shown in FIG. 4, indication of whether system resources are locked is typically stored in NVRAM 108 through a system resource lock flag 400. Nonvolatile RAM 108 can be a CMOS memory device or any other memory device capable of retaining stored information after system 100 is powered down.

If system resources are not locked (the `no` prong of step 304), any possible resource settings (PRS) and the CRS for each plug-and-play device are loaded into system RAM 104 at a location known by the operating system in steps 306 and 308 respectively.

If resources are locked (the `yes` prong of step 304), only CRS data is loaded into system RAM 104 where the operating system can access it. Following completion of BIOS start-up routines, the ACPI operating system is loaded and given control of computer system 100 (step 310).

Referring to FIG. 5, configuration information 500 (CRS and PRS) is generally copied 502 into a first location 504 in system RAM 104 during POST processing. While an ACPI operating system may physically access this first location 504, information about what data is stored there is not generally known (is opaque) to the operating system. That is, configuration information initially copied into system RAM 104 from system ROM 106 is not functionally accessible to the operating system. During step 306 (see FIG. 3) PRS information is copied 506 from the first location 504 into a second location 508 that the ACPI operating system is cognizant of. CRS information is similarly copied during step 308 of FIG. 3. When configuration data is in memory at a location known by the operating system 508, it has been loaded.

Referring again to FIG. 3, if the user wants to change one or more system resource settings (the `yes` prong of step 302), system 100 can be notified through a key stroke command such as F10. When the BIOS receives a modify command (e.g., via F10), it executes a low-level system set-up application which prompts the user to enter changes. If system resources are locked (the `yes` prong of step 312), the user is prompted for a password. If the entered password is correct (the `yes` prong of step 314), user specified changes and accepted and stored in NVRAM 108 (step 316). After a resource assignment is changed, or if the user supplied password is incorrect (the `no prong of step 314), start-up processing begins again at step 302.

A feature of the invention is that when system configuration data is locked, PRS data is segregated from CRS data and is not available to an ACPI operating system. This allows a computer system designer to implement a device configuration locking mechanism which is not available in a standard ACPI computer system. More generally, this approach hides computer system hardware features from an ACPI operating system such as thermal models and input-output configuration data.

The foregoing description is illustrative only and is not to be considered limiting. Various changes in the materials, components, circuit elements, as well as in the details of the illustrated operational method are possible without departing from the scope of the claims. For example, either system bus 112 or secondary bus 116 can be proprietary or special purpose buses, peripheral component interface (PCI) buses, industry standard architecture (ISA) buses, extended industry standard architecture (EISA) buses, or combinations of one or more of these busses. Further, PRS, CRS, and other ACPI table data can be stored in system ROM 108 in a compressed format to minimize memory usage. Device configuration information can also be stored in a different memory device than the system BIOS instructions. Steps of the invention may be performed by a computer processor executing instructions organized into a program module. Storage devices suitable for tangibly embodying computer program instructions include all forms of nonvolatile memory including, but not limited to: semiconductor memory devices such as EPROM, EEPROM, and flash devices; magnetic disks (fixed, floppy, and removable); other magnetic media such as tape; and optical media such as CD-ROM disks.