Computer system having two DMA circuits assigned to the same...

Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output addressing

Reexamination Certificate

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Details

C710S002000

Reexamination Certificate

active

06209042

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an information processing system that can be mounted on a docking station, and to a control method therefor; and in particular to an information processing system that can precisely perform DMA transfer operations even if DMA controller chips are used in both the information processing system and the docking station, and to a control method therefor.
More specifically, the present invention pertains to an information processing system that can precisely perform DMA transfers even if DMA controller chips exist both in a local system and a docking station, and to a control method therefor; and particularly to an information processing system that can preferably perform DMA transfer operations even if the same I/O port address is assigned for coexisting DMA controllers, and to a control method therefor.
As a consequence of recent technical developments, various types of personal computers (PCs), such as desktop types and notebook types, have been produced and are available on the market.
In a computer system, a Central Processing Unit or CPU for controlling the operation of an entire system communicates with memory and other peripheral devices across a common signal transfer path called a “bus”. The “bus” consists of multiple signal lines, such as a data signal line, an address signal line and a control signal line.
The ISA (Industry Standard Architecture) bus is widely known as a standard bus architecture. The ISA bus was adopted for the IBM PC/AT (PC/AT is a trademark of IBM Corp.), i.e., was designed for a CPU chip 80286 (with a local bus width of 16 bits) that is produced by Intel Corp. The primary performance features of the ISA bus are a 16-bit bus width, an operating clock of 8 MHz, and a maximum transfer speed of 4 mbps. The ISA bus, a de facto standard of a bus architecture, is the most popular, and many compatible (i.e., mountable and normally operating) expansion boards, peripheral devices and software programs (OS, BIOS, applications, etc.) are provided for it. In other words, the ISA bus is a legacy bus that has inherited much from the past.
Since at the beginning almost all CPU chips were operated at relatively low clock speeds, such as 8 MHz or 12 MHz, the ISA bus could be operated at the same clock speeds as those of the CPUs. However, as the performance available with CPU chips has been increased (e.g., 486 or Pentium, produced by Intel Corp., or PowerPC 6xx developed by IBM Corp. (PowerPC is a trademark of IBM Corp.)), the ISA bus has steadily hindered the utilization of improvements to the CPUs. Further, there has been an increase in the devices (adaptor cards) that require high speed data transfer, such as graphic video sub-systems, full motion video sub-systems, SCSI (Small Computer System Interface) storage sub-systems, and network sub-systems, and these devices do not function satisfactorily with the ISA bus.
The PCI (Peripheral Component Interconnect) architecture bus can compensate for the slow data transfer speed of the ISA bus. The PCI bus is a bus that was originally proposed by Intel Corp., which published the specifications in 1991, with which high speed operation is possible. Its primary performance features are a 32-bit bus width, an operating frequency of 33 MHz, and a maximum transfer speed of 132 mbps. Another feature of the PCI bus is that it is so designed that it can be connected to all other buses by using bridge circuits. For example, a PCI bus can be mutually connected to a CPU by a “host-PCI bridge circuit”, to an ISA bus by a “PCI-ISA bridge circuit”, and to another PCI bus by a “PCI—PCI bridge circuit”. Since the individual buses connected by bridge circuits are driven independently, i.e., asynchronously, no problem concerning electrical characteristics and operating stability arises.
While some current high performance PCs employ an ISA bus for which hardware and software assets are abundant, other PCs have adopted PCI buses as high speed buses that are used for graphic processing. In
FIG. 8
is schematically shown the hardware arrangement of a high performance PC. As is shown in
FIG. 8
, the system has a two layered structure, such as a PCI bus (local bus)
16
and an ISA bus (system bus)
22
. A processor bus
12
, that is directly connected to an external pin of a CPU
11
, communicates with the PCI bus
16
via a bridge circuit (host-PCI)
14
. To the PCI bus
16
are connected to devices, such as a video controller
17
A, for which relatively high speed operations are required. The ISA bus
22
communicates with the PCI bus
16
via a bridge circuit (PCI-ISA)
20
, and is also connected to relatively low speed operating devices, such as a floppy disk controller (FDC), a serial port, a parallel port, a keyboard
26
, and a mouse
27
,
To this point, an explanation has been given for a common personal computer without defining it as a desktop or a notebook type. However, a notebook computer, for which compact size, light weight, and portability are important, must be clearly distinguished from a desktop computer. For example, as a notebook computer is small and has less available storage space, and the surface area of the notebook computer is small, the number of bus slots that can be installed is very limited (while it is not rare for a desktop computer to have ten or more bus slots, for a laptop
otebook computer, no bus slots, or one or two at most, are provided.). Although portability is the biggest feature of a notebook computer, if cables (e.g., a printer cable, a monitor cable, and a communication cable) must be attached to and detached from the ports on the computer body each time the computer is to be used on a desk or to be removed from the desk, the handling will be complicated and the portability will also be deteriorated.
A so-called docking station (also called an “expansion box” or an “expansion unit”) provides for a notebook computer the same working environment as that of a desktop computer, without any deterioration of the portability of the notebook computer, when the notebook computer is to be used in the office. The primary functions of the docking station are “port replication” and “bus expansion”, The port replication can be realized by the expanding the connection ports of the notebook computer. That is, when a cable is connected in advance.to each port of the docking station, a user can immediately use a printer, a monitor and a network simply by mounting the notebook computer on the docking station. The bus expansion can be realized by expanding the bus in the notebook computer and the provision of a bus slot. Therefore, a user can insert desired adapter cards into a docking station without any restriction. It should be noted that a docking station is disclosed in, for example, Japanese Patent Application No. Hei 06-134124 (Our ref. No. JA9-94-030), which was assigned to the present applicant.
Most of the conventional docking stations are those for expanding an ISA bus in a system. This follows from the fact that the ISA bus has a significant legacy. However, there is a recently increased demand for the expansion of local buses, i.e., PCI buses. This is because the number of adapter cards that can be inserted into a single PCI bus is limited to ten at most in order to maintain the electric characteristic and the stability of the PCI bus (it should be noted that a device connected by a connector is regarded as two devices).
FIG. 9
is a schematic diagram illustrating the hardware arrangements for a docking station providing a bus expansion function for a PCI bus, and a notebook computer that is coupled to the docking station. As is shown in
FIG. 9
, the docking station has not only a PCI bus (a secondary PCI bus)
50
but also an ISA bus (a secondary ISA bus)
53
for the purpose of inheriting the legacy available for the ISA bus. The secondary PCI bus
50
and ISA bus
53
communicate with each other via a bridge circuit (PCI-ISA)
51
. A PCI bus (a primary PCI bus)
16
in the notebook computer and the secondary PCI bus
50
communicate with

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