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SCSI Interface Product Manual, Rev. B
k. Tasks for this initiator were changed by another initiator.
l. The version or level of microcode has changed.
m. The logical unit inventory has been changed (not generally applicable to Seagate disc drives); or
n. A change in the condition of a synchronized spindle occurred (not generally applicable to Seagate disc
drives).
The Unit Attention Parameters page (page 00h, bit 4 of byte 2) of the Mode Select command controls whether
or not a CHECK CONDITION status is to be reported to affected initiators when a Unit Attention condition
exists (see Table 145).
Logical units may queue unit attention conditions. After the first unit attention condition is cleared, another unit
attention condition may exist (e.g., a power on condition followed by a microcode change condition).
The Unit Attention condition for a particular initiator is cleared when that initiator does one of the following:
a. It sends a REQUEST SENSE command; or
b. It sends any other legitimate command, with the exception of the INQUIRY command. The INQUIRY com-
mand does not clear the Unit Attention condition.
When a Unit Attention condition flag is stored in the drive for a SCSI initiator port, the commands that initiator
issues to the drive operate as described in the following paragraphs.
If a SCSI initiator port sends an INQUIRY command to the drive when the drive has stored a Unit Attention
condition flag for that initiator (before the drive generates the auto contingent allegiance condition), the drive
shall perform the INQUIRY command and shall not clear the Unit Attention condition.
If a SCSI initiator port sends a REQUEST SENSE command to the drive when a Unit Attention condition flag is
stored for that initiator (before the drive generates the auto contingent allegiance condition), the drive shall dis-
card any pending sense data, report the Unit Attention sense key, and clear the Unit Attention condition
(negate the flag) for that initiator.
If a SCSI initiator port issues a command other than INQUIRY or REQUEST SENSE while a Unit Attention
condition flag is stored for that initiator, the drive may or may not perform the command and report CHECK
CONDITION status, depending on whether or not the Unit Attention bit is zero or one in the Unit Attention
Mode Parameters page (Page 00h, bit 4 of byte 2). See Table 145. If a REQUEST SENSE is issued next, the
Unit Attention condition is reported and cleared (flag negated) as noted in the preceding paragraph. If another
command other than REQUEST SENSE or INQUIRY is issued instead, the drive shall perform the command
and return the appropriate status. The Unit Attention condition for the subject initiator is cleared (flag negated)
and the sense data and flag indicating there has been a Unit Attention condition are lost.
7.6.7
Target hard reset
a SCSI target port hard reset is a SCSI target port response to a SCSI target port Reset task management
request (see SCSI Architecture Model-2, T10/1157D), or a reset event within the service delivery subsystem.
The definition of target reset events is protocol and interconnect specific. Each SCSI product standard shall
specify the response to a SCSI target port reset event including the conditions under which a SCSI target port
hard reset shall be executed.
To execute a hard reset, a SCSI target port shall initiate a logical unit reset for all attached logical units as
described in Section 7.6.8.
7.6.8
Logical unit reset
A logical unit reset is a response to a Logical Unit Reset task management request (see SCSI Architecture
Model-2, T10/1157D), or some other logical unit reset event, such as a SCSI target port hard reset (see Sec-
tion 7.6.7). The definition of such events may be device-specific or dependent on the protocol and interconnect.
Each appropriate SCSI standard shall specify the conditions under which a logical unit reset shall be executed.
To execute a logical unit reset the logical unit shall:
1. Abort all tasks in its task set;
2. Clear an auto contingent allegiance condition, if one is present;
3. Release all SCSI device reservations;
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