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The drive recovery option, is to continue execution of commands in the queue after the contingent allegiance
condition has cleared. The drive returns Busy status to all other initiators while the contingent allegiance condi-
tion exists. During this time all commands in the queue are suspended. All commands used for recovery oper-
ations are untagged commands.
Deferred errors are normally related to a command that has already completed. As such, there is no attempt to
return the queue tag value assigned to the original command.
7.8
Parameter rounding
Certain parameters sent to a SCSI target port with various commands contain a range of values. Targets may
choose to implement only selected values from this range. When the target receives a value that it does not
support, it either rejects the command (CHECK CONDITION status with Illegal Request Sense key) or it
rounds the value received to a supported value. The target shall reject unsupported values unless rounding is
permitted in the description of the parameter.
Rounding of parameter values, when permitted (Rounding is enabled by MODE SELECT command, page
code 00h, byte 2, bit 2) shall be performed as follows:
a SCSI target port that receives a parameter value that is not an exact supported value shall adjust the value to
one that it supports and shall return CHECK CONDITION status with a sense key of Recovered Error. The
additional sense code shall be set to Rounded Parameter. The initiator is responsible to issue an appropriate
command to learn what value the target has selected.
Implementors Note: Generally, the target should adjust maximum-value fields down to the next lower sup-
ported value than the one specified by the initiator. Minimum-value fields should be rounded up to the next
higher supported value than the one specified by the initiator. In some cases, the type of rounding (up or down)
is explicitly specified in the description of the parameter.
7.9
Programmable operating definition
Some applications require that the operating definition of a logical unit be modified to meet the special require-
ments of a particular initiator. The program-controlled modification of the operating definition is provided to
allow operating systems to change the operating definition of a more recently developed target to one which is
more compatible with the operating system. This ability requires that the system comply with the low-level
hardware definitions of SCSI-2.
The parameters that can be changed by modifying the operating definition of a logical unit include the vendor
identification, the device type, the device model, the SCSI compliance level, the SCSI specification level, the
command set, and other parameters. The low-level hardware parameters including signal timing and parity
definitions cannot be changed by modifying the operating definition. The present operating definition of a logi-
cal unit with respect to a SCSI initiator port can be determined at any time by execution of an INQUIRY com-
mand. In some vendor-specific cases, it may also be necessary to perform other commands including MODE
SENSE and READ CAPACITY.
The more recent Seagate drives do not support the Change Operating Definition command (see individual
drive's Product Manual).
Each logical unit begins at a particular operating definition. If the logical unit supports the CHANGE DEFINI-
TION command, the present operating definition can be changed to any other operating definition supported
by the logical unit. The actual details of the operating definition of a logical unit are vendor-specific. If the oper-
ating definition is changed to one that does not include the CHANGE DEFINITION command, the target contin-
ues to accept the CHANGE DEFINITION command.
If an error occurs during execution of a CHANGE DEFINITION command, the original operating definition
remains in effect after the command is executed. The new operating definition becomes active only after suc-
cessful execution of the CHANGE DEFINITION command.
Parallel SCSI Interface Product Manual, Rev. A
149
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