Sense Data; Asynchronous Event Reporting - Seagate SCSI Interface Product Manual

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b. The target supports the logical unit, but the peripheral device is not currently attached to the target. In
response to an Inquiry command the target shall return the Inquiry data with the peripheral qualifier set to
the value required in the SPC-2 standard. In response to a Request Sense command, the target shall return
sense data. The sense key shall be set to Illegal Request and the additional sense code shall be set to Log-
ical Unit Not Supported.
In response to any other command except Request Sense and Inquiry, the target shall terminate the com-
mand with Check Condition status. Sense data shall be set to the values specified for the Request Sense
command above;
c. The target supports the logical unit and the peripheral device is attached, but not operational. In response
to an Inquiry command the target shall return the Inquiry data with the peripheral qualifier set to the value
required in Section 5.0. In response to Request Sense, the target shall return sense data.
The target's response to any command other than Inquiry and Request Sense is vendor specific; or
d. The target supports the logical unit but is incapable of determining if the peripheral device is attached or is
not operational when it is not ready.
In response to an Inquiry command the target shall return the Inquiry data with the peripheral qualifier set to
the value specified in Section 5.0. In response to a Request Sense command the target shall return the
Request Sense data with a sense key of No Sense unless an auto contingent allegiance exists. The target's
response to any other command is vendor specific.
4.6.4

Sense data

Sense data shall be made available by the logical unit in the event a command completes with a Check Condi-
tion status or other conditions. The format, content and conditions under which sense data shall be prepared
by the logical unit are specified in this manual, the SPC-2 standard, and applicable SCSI-3 protocol standard.
Sense data shall be preserved by the logical unit for the initiator until it is transferred by one of the methods
listed below or until another task from that initiator is entered into the task set.
The sense data may be transferred to the initiator through any of the following methods:
a. The Request Sense command specified in Section 5.0;
b. An asynchronous event report; or
c. Autosense delivery.
The following clauses describe the last two transfer methods.
4.6.4.1

Asynchronous Event Reporting

Asynchronous Event Reporting is used by a logical unit to signal another device that an asynchronous event
has occurred. The mechanism automatically returns sense data associated with the event. Support for asyn-
chronous event reporting is a logical unit option.
The control mode page contains parameters affecting the use of asynchronous event reporting (see Section
5.0).
Asynchronous Event Reporting is used to signal a device that one of the four events listed below has occurred:
a. an error condition was encountered after command completion;
b. a newly initialized device is available;
c. some other type of unit attention condition has occurred; or
d. an asynchronous event has occurred.
An example of the first case above occurs in a device that implements a write cache. If the target is unable to
write cache data to the medium, it may use an asynchronous event report to inform the initiator of the failure.
An example of the second case above is a logical unit that generates an asynchronous event report, following
a power-on cycle, to notify other SCSI devices that it is ready to accept I/O commands.
Sense data accompanying the report identifies the condition (see Section 4.6.4).
An error condition or unit attention condition shall be reported to a specific initiator once per occurrence of the
event causing it. The logical unit may choose to use an asynchronous event report or to return Check Condition
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