SCSI-3 Reseved Fields and Codes

Charles Monia, SHR3-2/W3, 237-6757 04-May-1994 1504 monia at starch.enet.dec.com
Wed May 4 12:03:30 PDT 1994


Your proposal states:
==============================
"Reserved fields and code values within a data structure
specified by this or any other SCSI-3 standard are set aside for
future standardization.  Their use and interpretation may be
specified by future extensions to these standards.  A reserved
field shall be set to zero, or in accordance with a future
extension to the applicable SCSI-3 standard.

A  logical unit which receives a command descriptor block or
command data containing a non-zero reserved field or reserved
code value should terminate the command with CHECK CONDITION
status. If a CHECK CONDITION status is provided, the 
sense key shall be set to ILLEGAL REQUEST (see the
SPC standard).  It shall also be acceptable for a  logical unit
to interpret such fields  or code values in accordance with a
future revision to an SCSI-3 standard.  If the logical unit
chooses not to terminate the command with CHECK CONDITION, it
may ignore those values which are not defined for it and
continue operation as if those values were set to the default
or reserved state.  [The operation of a device in such an
environment may not be predictable.]"
========================================

The second paragraph states:

"...[The logical unit] may ignore those values which are not defined for it and
continue operation as if those values were set to the default
or reserved state. "

Is this globally acceptable behavior or does it only apply to logical units?
If the former, this should appear in the first paragraph.


I though the notion of unpredictable behavior applied to protocols as well as
logical units. If so, I'd suggest deleting the last sentence of the second
paragraaph (marked with square brackets] and modifying paragraph one to read:

"...A reserved field shall be set to zero, or in accordance with a future
extension to the applicable SCSI-3 standard. A reserved field that is
not set in this manner may cause unpredictable device behavior."


The following is exrtacted from rev 10H of the SCSI-2 spec:
=================================
6.1.1 Reserved

Reserved bits fields bytes and code values are set aside for future 
standardization. Their use and interpretation may be specified by future 
extensions to this standard. A reserved bit field or byte shall be set to zero 
                                                           ^^^^
or in accordance with a future extension to this standard. A target that 
receives a reserved bit, field or byte that is not zero or receives a reserved 
code value shall terminate the command with a CHECK CONDITION status. and the 
sense key shall be set to ILLEGAL REQUEST. It shall also be acceptable for a 
target to interpret a bit field, byte or code value in accordance with a future 
extension to this standard.
============================

Your proposal eliminates the SCSI-2 requirement as it applies to  CDB fields. 
While I have no objection to this, I believe it should be brought to the 
attention of the working group.


Charles Monia
==============================================================
Charles Monia
C/O:
Digital Equipment Corporation
334 South Street
Shrewsbury, MA 01545

Tel: (508)841-6757		Email: monia at starch.email.dec.com
Fax: (508)841-6100









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