Electrical computers and digital data processing systems: input/ – Input/output data processing – Peripheral adapting
Reexamination Certificate
2000-08-17
2003-09-23
Lefkowitz, Sumati (Department: 2189)
Electrical computers and digital data processing systems: input/
Input/output data processing
Peripheral adapting
C709S241000
Reexamination Certificate
active
06625676
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device configurable to exchange data with a digital computer across a Small Computer System Interface (SCSI) bus.
BACKGROUND TO THE INVENTION
It is known to connect digital computers to peripheral devices which may be physically distinct from the digital computer or contained within a same casing as a motherboard of the digital computer. Such peripheral devices typically include direct-access storage devices such as disk drives from which data stored on the disk drives may be recovered in any order. Additionally peripheral devices include sequential access storage devices, typically magnetic tape data storage devices, in which data must be recovered sequentially.
Referring to
FIG. 1
herein there is illustrated a conventional digital computer
100
having access to a data storage device
120
. The digital computer
100
and data storage device
120
are typically configured to exchange data across a cable connection
110
. A conventional means for interfacing a computing entity such as a digital computer with a peripheral device such as a disk drive or magnetic tape data storage device is described by the Small Computer System Interface (SCSI). By way of example, referring to
FIG. 1
herein digital computer
100
is configured to exchange data with a SCSI compatible device
120
across a small computer system interface bus carried across cable connection
110
.
Referring to
FIG. 2
herein, there is illustrated schematically a first example of a conventional small computer system interface configuration. By way of example, digital computer
200
is configured to exchange digital data with a plurality of peripheral devices
204
,
205
. Peripheral devices
204
,
205
may be disk drives, printers, optical-disks, magnetic tape data storage devices or the like, which are SCSI compatible. Processors operating within digital computer
200
requiring to initiate a transfer of data to peripheral devices
204
,
205
transfer data across SCSI bus
202
via a host bus adapter
201
and a controller
203
.
Referring to
FIG. 3
herein, there is illustrated another conventional SCSI configuration comprising a single initiating device such as a digital computer
300
sending and receiving data to and from multiple target devices
301
,
302
,
303
and
304
across a SCSI bus
305
via controllers
306
and
307
.
Referring to
FIG. 4
herein there is illustrated schematically, in more detail, the conventional SCSI configuration illustrated in
FIG. 2
herein, the SCSI configuration comprising a single initiating device and a single target device. Digital computer
200
includes a memory means which may be logically sub-divided into a user memory area and a memory area
400
allocated to an operating system kernel (OS/kemel). Conventionally, it is known to generate application software which is configurable to exchange data with a peripheral device
401
. Application software
402
may be a computer program for performing back-up operations. Associated with application software
402
is a corresponding respective driver program
403
which is configurable to act as an interface between application software
402
and a SCSI host bus adapter driver program
404
. Each application program operating within the memory means of digital computer
200
has a corresponding respective driver program configurable to interface each application program with SCSI host bus adapter card.
405
. The host bus adapter card
405
is physically connected to peripheral device
401
via SCSI bus
202
. Contained within a memory means of peripheral device
401
is a logical unit
406
configurable to exchange data and commands originated from application program
402
with a SCSI commands block
407
.
In conventional SCSI technology, and as described herein, a logical unit is a logical representation of a device such as peripheral device
401
. A logical unit is identified by an integer number which is also known herein as a Logical Unit Number (LUN). Each target device logically connected to a SCSI bus has one or more logical units associated with it. A physical device may have up to eight logical units associated with it, each logical unit having a unique identifying integer in the range 0 . . . 7. Each physical device
402
connecting to a SCSI bus has a unique identifier. Hence, each logical unit within a physical device
402
is also uniquely addressable by, for example, application program
402
resident within the OS/kernet of digital computer
200
by specifying the unique identifier of the device, and the logical unit identifying integer within the physical device.
Referring to
FIG. 5
herein, there is illustrated schematically a SCSI configuration comprising a plurality of user applications resident within an OS/kemel
400
of digital computer
200
. In addition to a data back-up program
402
it is known to configure an application program
500
within the OS/kemel having a corresponding respective driver program
501
which is also configurable to exchange data with device
401
across the SCSI bus
202
. Application program
500
may be configured to, for example, check the status of device
401
. However, if the device
401
is a serial device such as a magnetic tape data storage device then if more than one application program attempts to send commands to the serial tape device
401
then dashes can occur at the software or physical SCSI level affecting an operation of the serial tape device
401
.
It is Important to be able to interrogate serial devices in a “transparent” fashion, that is to say, to obtain data, for example, data concerning the performance of the serial device, without affecting its performance.
SUMMARY OF THE INVENTION
Specific embodiments and methods according to the present invention aim to provide a means for interrogating serial small computer system interface devices in a manner which leaves their normal mode of operation unaffected and thereby enables the performance of such devices to be monitored, without reconfiguration or significant disruption of the basic functionality of those devices.
Additionally, it is a further aim of the present invention to enable modifications to such devices to be accomplished more easily.
According to first aspect of the present invention there is provided a device configurable to exchange data with a digital computer across a small computer system interface bus, said device comprising:
a first logical unit (
609
); and
a second logical unit (
610
);
characterized in that said second logical unit (
610
) is configured for receiving a command from said digital computer across said interface bus (
608
), said command requesting data concerning a status of said device, wherein said receipt of said command requesting said status data is received by said second logical unit substantially independently of an operation of said first logical unit.
According to a second aspect of the present invention there is provided a method for querying a status of a device configurable to exchange data with a digital computer across a small computer system interface bus the method comprising the steps of:
creating a first logical unit within said device;
creating a second logical unit within said device;
characterized by sending a command from said digital computer to said second logical unit across said interface bus requesting status data concerning said device, wherein said step of requesting said status data occurs substantially independently of an operation of said first logical unit.
According to a third aspect of the present invention there is provided a computing entity comprising:
a digital computer device;
a small computer system interface bus, wherein said digital computer device is connected to a first end of said interface bus; and
at least one peripheral device connected to a second end of said interface bus;
said computer entity characterized by further comprising:
a first logical unit logically located substantially within said peripheral device;
a second logical unit logically locate
Bathie Jon
Gold Stephen
Hewlett-Packard Development Company L.C.
Lefkowitz Sumati
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