Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus expansion or extension
Reexamination Certificate
1998-10-20
2002-10-01
Wong, Peter (Department: 2181)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus expansion or extension
C710S302000
Reexamination Certificate
active
06460106
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to docking of personal computer systems and particularly to a bus bridge that facilitates “hot” docking. More particularly, the present invention relates to an enhanced expansion bus bridge for connecting a computer system to a docking station without requiring the computer system to shut down or enter sleep mode during the docking sequence.
2. Background of the Invention
Many portable computer systems are capable of connecting to a docking station, or an expansion base. The docking station is not actually a part of the portable computer system per se, but instead comprises a separate unit that accommodates the computer. The portable computer electrically connects to the docking station usually by way of an expansion bus, such as a Peripheral Component Interconnect (PCI) or other suitable bus. Because of inherent size and weight restrictions, portable computers tend to require design tradeoffs such as small keyboards and graphics displays, crude cursor control devices, and a limited number of mass storage devices. The docking station (or simply “dock”) usually couples to peripheral devices, such as a CD ROM drive, a standard size keyboard, and a large monitor and thus converts the portable computer into a desktop system. Accordingly, the computer user can access valuable features such as additional peripheral components including a large graphics display, a full-size mouse and keyboard, hard and floppy disk drives, CD ROM drives, Digital Video Disk (DVD) drives, and other peripheral components. An expansion base may also offer connections to a local area network (LAN), printer, and modem. Although intended primarily for desktop operation, the utilization of expansion bases has greatly enhanced the usability and comfort of laptop computer systems, handheld computers, and other portable systems, especially when the computer is used frequently in one location, such as in the home or office.
When the portable computer is docked, an expansion bus within the computer typically couples to an expansion bus in the docking station. The expansion bus permits communication (e.g., data transfers) between the computer and a peripheral device in the docking station. Because of the delicate nature of high performance expansion buses such as the PCI bus, care must be taken when designing a docking system and implementing the docking procedure to connect two PCI buses. One factor to consider is that a single expansion bus often can only support a limited number of components. Suddenly “loading” an expansion bus with too many components may severely degrade performance or crash the bus. To facilitate docking in portable computer systems, bus “bridge” devices have been developed that couple the expansion bus within the computer to the expansion bus inside the docking station. Because the computer expansion bus and dock expansion bus are not directly connected to one another, neither expansion bus becomes overloaded due to the docking connection.
FIG. 1
illustrates a representative conventional computer system/docking station configuration. The computer
100
generally includes a CPU coupled to a bridge logic device via a CPU bus. The bridge logic device is sometimes referred to as a “North bridge” for no other reason than it often is depicted at the upper end of a computer system drawing. The North bridge also couples to a main memory array by a memory bus. The North bridge couples the CPU and memory to the peripheral devices in the system through a PCI bus
125
or other expansion bus (such as an EISA bus). Various components that implement the PCI protocol may reside on the computer's PCI bus
125
, such as a graphics controller.
If other secondary expansion buses are provided in the computer system, another bridge logic device typically is used to couple the PCI bus
125
to that expansion bus. This bridge logic is sometimes referred to as a “South bridge,” reflecting its location vis-a-vis the North bridge in a typical computer system drawing. In
FIG. 1
, the South bridge couples the computer PCI bus
125
to an ISA bus. Various ISA-compatible devices are shown coupled to the ISA bus.
The South bridge may also support an input/output (I/O) controller that interfaces to basic input/output devices (not shown) such as a keyboard, a mouse, a floppy disk drive, and various input switches such as a power switch and a suspend switch. The I/O controller typically couples to the South bridge via a standard bus, shown as an ISA bus in
FIG. 1. A
serial bus, which generally is a bus with only one data signal, may provide an additional connection between the I/O controller and South bridge. The I/O controller typically comprises an ISA bus interface (not specifically shown) and transmit and receive registers (not specifically shown) for exchanging data with the South bridge over the serial bus.
The I/O controller generally has the capability to handle power management functions such as reducing or terminating power to components such as the floppy drive (not shown), blocking the clock signals that drive components such as the bridge devices and CPU, and initiating sleep mode in the peripheral buses. The I/O controller further asserts System Management Interrupt (SMI) signals to various devices such as the CPU and North bridge to indicate special conditions pertaining to input/output activities such as sleep mode. The I/O controller typically incorporates a counter or a Real Time Clock (RTC) to track the activities of certain components such as the hard drive and the PCI bus
125
, inducing a sleep mode or reduced power mode after a predetermined time of inactivity. The I/O controller may also place the computer system into a low-power mode, in which the power to all devices except the I/O controller itself shuts off completely.
The computer system also includes a bus bridge for coupling the expansion bus within the computer to an expansion bus housed in a docking station. A typical docking station
150
with a PCI bus
175
is pictured in FIG.
1
and coupled to the PCI bus
125
within the computer system. As shown, a PCI-to-PCI bus bridge device
130
couples the two PCI buses
125
and
175
. An exemplary PCI-to-PCI bridge device is the 21554 PCI-to-PCI bridge manufactured by Intel Corporation.
The docking station
150
pictured in
FIG. 1
also includes a South bridge logic (not shown specifically) for coupling components connected to the computer's PCI bus
125
to other components contained within the docking station
150
. Thus, as shown in
FIG. 1
, a South bridge logic device within the docking station couples the PCI bus
125
to various expansion buses including an ISA bus, a universal serial bus (USB), and an integrated drive electronics (IDE) bus. The docking station
150
also supports a local area network (LAN) connection such as Ethernet. In addition to the PCI signals that are provided between the computer
100
and the dock
150
, various “sideband” signals within the docking station
150
must be connected to the computer system
100
during docking. These sideband signals typically connect to the I/O controller but may be connected to virtually any component within the computer. Examples of sideband signals include power and ground signals, interrupt signals, and I/O signals such as serial and parallel port signals, keyboard and mouse signals, and audio and video signals. Accordingly, the South Bridge logic in the docking station
150
may incorporate an interrupt controller to generate the interrupt signals, and the docking station
150
may include dedicated I/O controllers coupled to the I/O devices and that transmit the sideband signals.
A significant problem inherent in docking relates to electrical “transients” and voltage mismatches that can occur when the connectors on the computer
100
and docking station
150
are first mated. When th
Chung-Trans X.
Compaq Information Technologies Group L.P.
Conley & Rose & Tayon P.C.
Wong Peter
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