Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output process timing
Reexamination Certificate
1999-04-27
2002-08-27
Lefkowitz, Sumati (Department: 2181)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output process timing
C710S016000, C710S100000
Reexamination Certificate
active
06442628
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to computer systems, and more particularly to methods for determining maximum communication rate between devices interconnected via I/O buses in a computer system.
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 attaching one or more peripheral devices such as disk drives, tape drives, printers, scanners, optical drives, and the like. Generally, the peripheral devices are attached to the computer system by means of a bus (e.g., cable).
One of the most popular buses is the well known small computer systems interface (SCSI) bus, which is defined in conformity with 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 system and its peripheral devices. The SCSI interfaces may be operated over a wide range of media and transfer rates. For example, Table 1 illustrates representative parameters for data throughput of exemplary SCSI interfaces.
TABLE 1
Number
of Data
Bus
Data
Bits
Speed
Signal
Throughput
Names
(Width)
(MHz)
Type
(MB/sec)
SCSI-1
8
5
SE
5
SCSI-2
8
5
SE
5
Fast SCSI-2
8
10
SE
10
Fast-Wide SCSI-2
16
10
SE
20
Ultran SCSI
16
20
SE
40
Ultra2 SCSI
16
40
LVD
80
Ultra 160/M
16
40
LVD
160
As shown in Table 1, the data throughputs of the SCSI buses vary as the number of data bits transferred, the bus speed, and the type of signal are changed. For example, the maximum data throughput (e.g., data transfer rate) of Ultran SCSI bus is four times that of SCSI-2 bus. This is because the number of data bits transferred and the bus speed of the former bus is twice that of the latter.
The signal type also affects the transfer rate as shown in Table 1. Recently, the Ultra2 SCSI specification has been adopted in the industry to provide greater data transfer rate and cable length. It defines a new Low Voltage Differential (LVD) I/O interface, which uses a pair of wires to carry a signal. This allows for faster data rate of 80 MB/sec and a longer cable (up to 12 or 25 meters depending on load) with less susceptibility to noise than traditional single-ended (SE) signaling.
As is well known in the art, an SCSI bus is generally implemented as a cable having a set of wires. For example, the SCSI-1 cable has 50 wires. Of these 50 wires, 8 wires are for data, 1 wire is for parity, 9 wires are for control, 25 wires are for ground, and the remaining wires are for power or are reserved for future use. The 8 data wires are used to carry 8 bits of data in parallel.
In general, an SCSI bus may accommodate a plurality of SCSI devices up to a number equal to the number of data bits in the SCSI bus. For example, the SCSI-2 bus may accommodate up to eight devices, of which one is usually an SCSI host adapter. The SCSI host adapter functions to convert or otherwise translate signals between the host computer and the peripheral devices.
FIG. 1A
illustrates a block diagram of an exemplary computer system
100
having a host computer
102
, an SCSI host adapter
104
, a plurality of SCSI devices
106
, and an SCSI bus
108
. The host computer
102
is coupled to the SCSI host adapter
104
by means of a host bus
110
such as PCI bus or the like. The host adapter
104
is also coupled to the SCSI devices
106
by means of the SCSI bus
108
. Under the current SCSI specifications, the SCSI bus
108
may interconnect up to 7 or 15 target SCSI devices
106
to the host adapter
104
depending on the type of SCSI bus implemented. The target SCSI devices
106
may be devices such as disk drives, tape drives, printers, scanners, optical drives, or any other devices that meet the SCSI specification.
In this arrangement, the host adapter
104
controls communication between the host computer
102
and the SCSI devices
106
. Specifically, the host adapter
104
is configured to receive data, address, and control signals from the host computer
102
via the host bus
110
and convert the signals into corresponding SCSI compatible data, address, and control signals. Similarly, the 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.
FIG. 1B
is a more detailed block diagram of the host adapter
104
having an SCSI host adapter chip
112
, an SCSI bus interface
114
, a host interface
116
, and a ROM
118
. The host interface
116
is configured to provide a physical connection to the host bus
110
. The SCSI host adapter chip
112
is configured to interface with the host and SCSI bus interfaces
116
and
114
. The SCSI host adapter chip
112
is well known in the art and may be implemented, for example, by using ACI-7890A packaged semiconductor device, which is available from Adaptec Inc., of Milpitas, Calif.
The SCSI host adapter chip
112
uses the ROM
118
to store operating instructions that can be read into the memory of the host computer system
102
and executed by a host processor to communicate with the host adapter
104
. The operating instructions stored within the ROM
118
typically include either a BIOS image or some other type of host-bus compatible platform operating system driver.
Currently, when the computer system
100
powers up, the SCSI host adapter
104
, as initiator, interrogates the SCSI bus
108
to determine which devices are connected to the bus
108
. This scan of the bus is done by the operating system module (OSM) part of the BIOS code. The interrogation consists of the initiator arbitrating for the bus, winning the arbitration, and selecting each device ID to check for a response from an associated SCSI device. If a particular ID responds, the initiator sends an INQUIRY command and the device responds with data identifying the device such as manufacturer, serial number, etc.
At boot-up, the host adapter
104
accesses the ROM
118
and attempts to recognize devices connected to the SCSI bus
108
. In addition, it performs initial testing on speed and width of the SCSI bus
108
and starts boot process. However, users often connect the SCSI devices and cable in violation of SCSI specification. For example, the BIOS in the ROM
118
may be set to a speed higher than what the computer system
100
is capable of handling. As a result, the boot process fails and an error condition is generated. In response, the user manually resets the parameters to a different bus speed and/or width in the BIOS of the host adapter and reboots the computer system
100
.
Unfortunately, this trial and error process imposes a substantial burden for many users in terms of time and labor needed to manually set the parameters for proper boot-up and operation. In addition, the speed thus set is often lower than what the system is capable of operating reliably. For example, users often set the parameters of host adapters to operate at a lowest possible speed (e.g., 5 MB/sec) to provide the least probability of failure. This means that the computer system may operate at less than its full capacity. Hence, the resources of the computer system are not efficiently utilized.
In view of the foregoing, there is a need for a method and system for setting data throughput parameters to provide the highest data throughput between a host adapter and a target device over a bus without requiring users to manually adjust and set bus parameters.
SUMMARY OF THE INVENTION
The present invention fills these needs by providing method and system for automatically determining maximum data throughput rate over a bus. 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
Bastiani Vincent J.
Lamers Lawrence J.
Adaptec, Inc.
Lefkowitz Sumati
Martine & Penilla LLP
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