Reserved byte bad bit reporting

Terry Spear terrys at
Tue Feb 23 09:52:29 PST 1999

* From the T10 Reflector (t10 at, posted by:
* Terry Spear <terrys at>

When a target detects a bit set in a reserved byte in a CDB (or Parameter
data) should the BPV and Bit Pointer fields be set in the sense data?  The
same question appears to be relevant to any whole or multi byte field as well.

The possibilties are set the SKSV and then the field pointer to the offset
of the reserved byte containing the set bit.  It appears that either of the
following implementations may be conforming:

1) Set BPV=1 and set the Bit Pointer field to 7
2) Set BPV=0

The relavent text from SPC2 (r02a) does not specify this behavior and thus
appears to make it "implementor's choice".  What interpretation are some
actual implementations using (Exabyte Library systems use BPV=0)?

Is there a defacto consensus?

If so I recommend that a clarification sentence be added to SPC2.

>From SPC2 (Request Sense section):

"A bit pointer valid (BPV) bit of zero indicates that the value in the bit
pointer field is not valid. A BPV bit of one indicates that the bit pointer
field specifies which bit of the byte designated by the field pointer field
is in error." 

"When a multiple-bit field is in error, the bit pointer field shall point
to the most-significant (left-most) bit of the field.  The field pointer
field indicates which byte of the command descriptor block or of the
parameter data was in error.  Bytes are numbered starting from zero, as
shown in the tables describing the commands and parameters. When a
multiple-byte field is in error, the pointer shall point to the most-
significant (left-most) byte of the field. If several consecutive bytes are
reserved, each shall be treated as a single-byte field."

 Terry L. Spear			Interface Solutions Group
 terrys at		Breakthrough Systems Inc.
 303-661-0355				12400 Arapahoe Road
 303-661-9707 (fax)			Lafayette, CO  80026
 SCSI+Fibre Channel Target Firmware, Testing, Host Drivers, Apps
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