Tracking PCI bus numbers that change during re-configuration

Details Tracking PCI bus numbers that change during re-configuration Tracking PCI bus numbers that change during re-configuration

1999-03-02

2002-05-28

Lee, Thomas (Department: 2182)

Electrical computers and digital data processing systems: input/

Input/output data processing

Peripheral configuration

C710S009000, C710S104000

Reexamination Certificate

active

06397268

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to computers that auto-configure peripheral devices connected thereto, and more particularly in determining the peripheral device bus number when another peripheral device bus is added which changes the original peripheral device bus number in the computer.
2. Description of the Related Technology
Use of computers, especially personal computers, in business and at home is becoming more and more pervasive because the computer has become an integral tool of most information workers who work in the fields of accounting, law, engineering, insurance, services, sales and the like. Rapid technological improvements in the field of computers have opened up many new applications heretofore unavailable or too expensive for the use of older technology mainframe computers. A significant part of the ever increasing popularity of the computer, besides its low cost relative to just a few years ago, is its ability to run sophisticated programs and perform many useful and new tasks. Computers today may be easily upgraded with new peripheral devices for added flexibility and enhanced performance.
A major advance in the performance of computers has been the implementation of sophisticated peripheral devices such as video graphics adapters, local area network interfaces, SCSI bus adapters, full motion video and the like. These sophisticated peripheral devices are capable of data transfer rates approaching the native speed of the computer central processing unit (“CPU”) or microprocessor. Tie peripheral devices data transfer speeds are achieved by connecting the peripheral devices to the microprocessor and associated random access memory through high speed expansion local buses. Most notably, a high speed expansion local bus standard has emerged that is microprocessor independent and has been embraced by a significant number of peripheral hardware manufacturers and software programmers. This high speed expansion bus standard is called the “Peripheral Component Interconnect” or “PCI.” A more complete definition of the PCI local bus may be found in the PCI Local Bus Specification, revision 2.1; PCI/PCI Bridge Specification, revision 1.0; PCI System Design Guide, revision 1.0; and PCI BIOS Specification, revision 2.1. These PCI specifications are available from the PCI Special Interest Group, P.O. Box 14070, Portland, Oreg. 97214.
A computer system has a plurality of informational (data and address) buses such as a host bus, a memory bus, at least one high speed expansion local bus such as the PCI bus, and other peripheral buses such as the Small Computer System Interface (SCSI), Extension to Industry Standard Architecture (EISA), and Industry Standard Architecture (ISA). The central processing unit (CPU) of the computer system communicates with main memory and with the peripherals that make up the computer system over these various buses. The main memory generally communicates over a memory bus through a cache memory bridge to the CPU host bus. The peripherals, depending on their data transfer speed requirements, are connected to the various buses which are connected to the CPU through bus bridges that detect required actions, arbitrate, and translate both data and addresses between the various buses. The choices available for the various computer system bus structures and devices residing on these buses are relatively flexible and may be organized in a number of different ways. One of the more desirable features of present day computer systems is their flexibility and ease in implementing custom solutions for users having widely different requirements.
Another advance in the flexibility and ease in the implementation of personal computers is the emerging “plug and play” standard in which each vendor's hardware has unique coding embedded within the peripheral device. Plug and play software in the computer operating system software auto configures the peripheral devices found connected to the various computer buses such as the various PCI buses, EISA and ISA buses. In addition, the plug and play operating system software configures registers within the peripheral devices found in the computer system as to memory space allocation, interrupt priorities and the like.
Plug and play initialization generally is performed with a system configuration program that is run whenever a new device is incorporated into the computer system. Once the configuration program has determined the parameters for each of the devices in the computer system, these parameters may be stored in non-volatile random access memory (NVRAM). An industry standard for storage of both plug and play and non-plug and play device configuration information is the Extended System Configuration Data (ESCD) format. The ESCD format is used to store detailed configuration information in the NVRAM for each device. This ESCD information allows the computer system BIOS configuration software to work together with the configuration utilities to provide robust support for all peripheral devices, both plug and play, and non- plug and play.
During the first initialization of a computer, the system configuration utility determines the hardware configuration of the computer system including all peripheral devices connected to the various buses of the computer system. Some user involvement may be required for device interrupt priority and the like. Once the configuration of the computer system is determined, either automatically and/or by user selection of settings, the computer system configuration information is stored in ESCD format in the NVRAM. Thereafter, the system configuration utility need not be run again. This greatly shortens the startup time required for the computer system and does not require the computer system user to have to make any selections for hardware interrupts and the like, as may be required in the system configuration utility.
However, situations arise more and more often which require rerunning the system configuration utility to update the device configuration information stored in the NVRAM when a new device is added to the computer system. One specific situation is when a PCI peripheral device interface card having a PCI-PCI bridge is placed into a PCI connector slot of a first PCI bus of the computer system. The PCI-PCI bridge, which creates a new PCI bus, causes the PCI bus numbers of all subsequent PCI buses to increase by one (PCI-PCI bridge may be a PCI interface card having its own PCI bus for a plurality of PCI devices integrated on the card or for PCI bus connector slots associated with the new PCI bus). This creates a problem since any user configured information such as interrupt request (IRQ) number, controller order number, etc., stored in the NVRAM specifies the bus and device/function number of the PCI device to which it applies. Originally, this information was determined and stored in the NVRAM by the system configuration utility during the initial setup of the computer system and contains configuration choices made at that time.
During normal startup of the computer system (every time the computer is turned on by the user), a Power On Self Test (POST) routine depends on prior information stored in the NVRAM by the system configuration utility. If the PCI bus numbers of any of the PCI cards change because a new PCI bus was introduced by adding a new PCI-PCI bridge to the computer, the original configuration information stored in the NVRAM will not be correct for those PCI cards now having different bus numbers, even though they remain in the same physical slot numbers. This situation results in the software operating system not being able to configure the PCI cards now having bus numbers different than what was expected from the information stored in the NVRAM. This can be especially bothersome for a PCI device such as a controller which has been configured as a system startup device, but now cannot be used to startup the computer system because its registers have not been initialized during POST to indicate that it is su

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