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Commands—introduction34
Parameter List check
For LOG SELECT, MODE SELECT and some diagnostic commands, the associated data sent to the
drive is in the form of parameter lists. These are described under the command names in the next
chapter. Checks are performed to test the following:
• Fixed and reserved fields have not been modified. Fixed fields are indicated by a number
in round brackets following the field name.
• A field has been set to an invalid value.
• The syntax of the page of parameters has been violated—for example, where a particular
value in one field imposes limitations on the valid range for another field.
If a field has been set to an illegal value,
CHECK CONDITION is reported to the host with a sense
key of
ILLEGAL REQUEST and additional sense of 2600h (invalid field in parameter list).
The drive scans the data in the Command Description Block from “left” (bit 7) to “right”, and
“down” (from byte 0 to byte n). It sets the field pointers to the first bit of the first bad field
encountered. If the bad field is contained in a contiguous group of fixed fields, the pointers
indicate the first bit of the first field in the group, even though the error may be in a later field in the
group.
NOTE: With MODE SELECT, the drive checks the integrity of the whole parameter list before acting on
any parameters, so all the mode parameters need to be correct before any of them are implemented.
Reservation check
This checks to see if the drive has been reserved for use by a host, and if it has, whether the host is
the same host that sent the command being executed.
If the drive has been reserved for some other host then
RESERVATION CONFLICT status is reported.
See the
RESERVE UNIT (page 164) and RELEASE UNIT (page 135) commands.
Unit Attention check
This checks if a UNIT ATTENTION condition exists for the host which sent the command. If it does,
the drive reports
CHECK CONDITION status with a sense key of UNIT ATTENTION. The remaining
sense data will be set according to the unit attention condition which exists. See Unit Attention
Sense in the description of the
REQUEST SENSE command on page 155.