Tape LOPU - long vs. short

Pat LaVarre LAVARRE at iomega.com
Mon Nov 4 13:02:36 PST 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Pat LaVarre" <LAVARRE at iomega.com>
*
Suppose data bytes[0] & x04 LOPU is set in the TCLP
LONG form of the Tape op x34 Read Position data ...
 
... should the LOPU necessarily be set in the short
form of the data?
 
What bothers me in the English of the text is that the
case of an unknown or not accurately reportable
partition number, specified in the long form, is not
mentioned in the discussion of the short form, even
though the PARTITION NUMBER field there is three bytes
shorter.
 
Also the English of ssc2r08e contradicts itself when
the object location is known but not accurately
reportable in the short form?
 
Thanks in advance, Pat LaVarre
 
P.S. Relevant quotes include:
 
// // // ssc2r08e.pdf:
 
"Table 37 -- READ POSITION data format, short form"
 
"A logical object position unknown (LOPU) bit of one
specifies the first and last object locations are not
currently known or not otherwise obtainable. A LOPU
bit of zero specifies the FIRST LOGICAL OBJECT
LOCATION and LAST LOGICAL OBJECT LOCATION fields
contain valid position information.
 
"Table 38 -- READ POSITION data format, long form"
 
"A logical object position unknown (LOPU) bit of one
specifies the partition number or logical object
number are not known or accurate reporting is not
currently available. A LOPU bit of zero specifies the
PARTITION NUMBER and LOGICAL OBJECT NUMBER fields
contain valid position information.
 
"The MPU and LOPU bits shall be set to one only if the
logical unit is unable to accurately determine or does
not know the current mark or logical object,
respectively.
 
// // // ssc-r22.pdf: much like ssc2r08e, except
"LOPU" was "BPU",  "object" was "block", and
"specifies" was "indicates".
 
"Table 20 -- READ POSITION data format, short form"
 
"A block position unknown (BPU) bit of one indicates
that the first and last block locations are not
currently known or not otherwise obtainable. A BPU bit
of zero indicates that the FIRST BLOCK LOCATION and
LAST BLOCK LOCATION fields contain valid position
information.
 
"Table 21 -- READ POSITION data format, long form"
 
"A block position unknown (BPU) bit of one indicates
that the partition number or block number are not
known or accurate reporting is not currently
available. A BPU bit of zero indicates that the
PARTITION NUMBER and BLOCK NUMBER fields contain valid
position information.
 
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