Target Hard Reset; Logical Unit Reset - Seagate SCSI Interface Product Manual

70
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:
1. It sends a Request Sense Command.
2. It sends any other legitimate command, with the exception of the Inquiry command. The Inquiry command
does not clear the Unit Attention condition.
When a Unit Attention condition flag is stored in the drive for an initiator, the commands that initiator issues to
the drive operate as described in the following paragraphs.
If an initiator 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 an initiator 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 discard any
pending sense data, report the Unit Attention Sense Key, and clear the Unit Attention condition (negate the
flag) for that initiator.
If an initiator 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 101. 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.
4.6.6

Target Hard Reset

A target hard reset is a target response to a Target Reset task management request (see T10/1157D), or a
reset event within the service delivery subsystem. The definition of target reset events is protocol and intercon-
nect specific. Each SCSI-3 product standard shall specify the response to a target reset event including the
conditions under which a target hard reset shall be executed.
To execute a hard reset, a target shall initiate a logical unit reset for all attached logical units as described in
Section 4.6.7.
4.6.7

Logical Unit Reset

A logical unit reset is a response to a Logical Unit Reset task management request (see T10/1157D), or some
other logical unit reset event, such as a target hard reset (see Section 4.6.6). The definition of such events may
be device-specific or dependent on the protocol and interconnect. Each appropriate SCSI-3 standard shall
specify the conditions under which a logical unit reset shall be executed.
To execute a logical unit reset the logical unit shall:
a. Abort all tasks in its task set;
b. Clear an auto contingent allegiance condition, if one is present;
c. Release all SCSI device reservations;
d. Return the device's operating mode to the appropriate initial conditions, similar to those conditions that
would be found following device power-on. The Mode Select conditions (see the SPC standard) shall be
restored to their saved values if saved values have been established. Mode Select conditions for which no
saved values have been established shall be returned to their default values;
e. set a Unit Attention condition (see Section 4.6.5).
f. Initiate a logical unit reset for all nested logical units.
In addition to the above, the logical unit shall execute any additional functions required by the applicable stan-
dards.
SCSI Interface Product Manual, Rev. J