Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output addressing
Reexamination Certificate
2001-03-02
2004-06-22
Gaffin, Jeffrey (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output addressing
C710S002000, C710S004000, C710S008000, C710S009000, C710S015000, C710S104000, C711S001000, C709S234000
Reexamination Certificate
active
06754720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to computer I/O subsystems having expanders, and more particularly to methods for automatically assigning addresses to expanders in I/O subsystems over peripheral buses.
2. Description of the Related Art
Modern computer systems often utilize one or more buses to connect to peripheral devices to enhance its resources. For example, the resources of a computer system may be substantially increased by connecting the computer system to one or more peripheral devices such as disk drives, tape drives, printers, scanners, optical drives, and the like. These peripheral devices are attached to the computer system by means of a peripheral bus (e.g., cable).
One of the most widely used peripheral buses is the well known small computer systems interface (SCSI) bus, which is defined in conformity with well known SCSI protocols (e.g., SCSI-1, SCSI-2, SCSI-3, etc.), which are incorporated herein by reference. The SCSI protocols are designed to provide an efficient peer-to-peer I/O interface between a host computer and its peripheral devices in a computer system.
FIG. 1
shows a block diagram of a conventional computer system
100
including a host computer
102
, a plurality of SCSI devices
106
, and a SCSI bus
108
. The host computer
102
includes a SCSI host adapter
104
for communicating with the SCSI devices
106
. The host adapter
104
in the computer system
100
controls communication between the host computer
102
and the SCSI devices
106
. For example, the host adapter
104
provides a physical connection between the host computer
102
and the SCSI bus
108
. In addition, it is configured to receive data, address, and control signals from the host computer
102
and convert the signals into corresponding SCSI compatible data, address, and control signals. Conversely, the SCSI host adapter
104
is also configured to receive SCSI compatible data, address, and control signals from the SCSI devices
106
through the SCSI bus
108
and convert them into corresponding host-bus compatible data, addressing, and control signals. The SCSI host adapter
104
is well known in the art and may be implemented, for example, by using AIC-7890A™ packaged semiconductor device, which is available from Adaptec Inc., of Milpitas, Calif.
Under the conventional SCSI specifications, the SCSI bus
108
may connect up to 16 SCSI devices including the host adapter
104
depending on the type of SCSI bus implemented. The SCSI devices
106
may be peripheral devices such as disk drives, tape drives, printers, scanners, optical drives, or any other devices that meet the SCSI specification. The SCSI bus
108
is typically implemented as a cable having a set of parallel wires. For example, the SCSI-1 cable has 50 wires. Of these 50 wires, eight wires are for data, one wire is for parity, nine wires are for control, 25 wires are for ground, and the remaining wires are for power or are reserved for future use. The eight data wires are used to carry eight bits of data in parallel. In general, conventional SCSI bus cables include either 8 or 16 data wires for carrying 8 or 16 bits, respectively, of data in parallel. The data wires in the bus thus define a datapath for communicating bits equal to the number of data wires in the bus.
A traditional SCSI bus may accommodate a plurality of SCSI devices up to a maximum number equal to the number of data bits in the SCSI bus. In practice, the width of the SCSI datapath is typically 8 or 16 bits corresponding to the number of data wires in the SCSI bus. This means the maximum number of SCSI devices, including a host adapter, that can be attached to a SCSI bus is limited to 8 or 16.
Conventional SCSI buses, however, are generally capable of transmitting signals reliably for a specified cable length only. For example, SCSI bus cables conforming to SCSI specifications are typically limited to a maximum length such as 3, 6, 12, or 25 meters, and the like. In modern computer systems such as servers that need to communicate with numerous SCSI devices, some SCSI peripheral devices may be located more than the specified cable length away from a host computer.
In such instances, an expander, which is essentially a repeater, is typically used to add another SCSI bus, which is then used to couple additional SCSI devices.
FIG. 2
illustrates a conventional computer system
200
that includes an expander
214
for connecting two SCSI buses
208
and
210
. In the computer system
200
, a host computer
202
is coupled to the SCSI bus
208
via a SCSI host adapter
204
. One or more SCSI devices
206
are coupled to the SCSI bus
208
while one or more SCSI devices
212
are coupled to the SCSI bus
210
. The expander
214
is coupled between the SCSI buses
208
and
210
to regenerate signals received on either SCSI bus
208
or
210
for transmission to the other SCSI bus. In this configuration, the expander
214
functions to extend the length of the overall SCSI bus so that additional SCSI devices
212
or expanders can be attached to the SCSI bus
210
. The SCSI devices
212
and SCSI bus
210
are collectively referred to as a segment. Similarly, the host adapter
204
, SCSI devices
206
, and SCSI bus
208
collectively define another segment.
Conventional expanders, however, are typically transparent devices without SCSI IDs of their own. This means that the expanders are not addressable and are thus invisible to SCSI protocol. Using such transparent expanders without dedicated SCSI IDs in an I/O subsystem presents several drawbacks. For example, individual segments of the I/O subsystem often need to be modified to isolate faulty cables, connections, drivers, and receivers. In addition, it is often desirable to communicate with individual expanders to determine optimum speed at which the expanders can communicate during domain validation.
Because conventional expanders are not addressable, these modifications and domain validation processes may not be performed automatically without a system administrator. One obvious solution would be to implement expanders like SCSI devices by adding SCSI controllers and assigning SCSI IDs used for SCSI devices. This solution, however, would reduce the number of addressable SCSI devices that can be attached to a SCSI I/O subsystem. Further, assigning SCSI addresses to expanders will typically require system administrators to keep track of SCSI IDs of all individual expanders and manually set the jumpers for the expander IDs. In a complex I/O subsystem with substantial number of SCSI devices and expanders, assigning SCSI IDs to expanders by manually setting the jumpers may be complicated and labor intensive.
In view of the foregoing, what is needed is a method for automatically addressing SCSI expanders without using valuable conventional SCSI IDs.
SUMMARY OF THE INVENTION
The present invention fills these needs by providing methods for automatically assigning addresses to intelligent expanders in an I/O subsystem. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium. Several inventive embodiments of the present invention are described below.
In one embodiment, the present invention provides a method for automatically assigning addresses to expanders in a computer I/O subsystem that is coupled to one or more host computers. The computer I/O subsystem includes one or more peripheral buses, a set of peripheral devices, and a set of expanders with each expander being arranged to couple a pair of peripheral buses. The peripheral devices are coupled to the peripheral buses. In this configuration, a host computer selects a peripheral device as a target device and writes an address data pattern to the selected target device. The host computer then selects the target device and reads the address data pattern from the target device. Unique addresses are then assigned to one or more expanders coupling the host computer and the tar
Adaptec, Inc.
Casiano Angel L.
Gaffin Jeffrey
Martine & Penilla LLP
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