Commands—Introduction 37
Commands—Introduction
Media Write Check
This checks whether the media is write-protected. If it is, CHECK CONDITION is
reported with a sense key of
DATA PROTECT and additional sense of 2700h
(write-protected).
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 141) and RELEASE UNIT (page 121) commands.
