11-036r9 Reserved Bits in TTIU

Penokie, George George.Penokie at lsi.com
Tue Jul 26 06:44:52 PDT 2011

Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1107261_f.htm">HTML-formatted message</a>

Although we have done that in some cases it is not the normal condition. The
general rule for reserved is:
"a keyword referring to bits, bytes, words, fields and code values that are
set aside for future standardization; a
reserved bit, byte, word or field shall be set to zero, or in accordance with
a future extension to this standard;
recipients are not required to check reserved bits, bytes, words or fields
for zero values; receipt of reserved
code values in defined fields shall be reported as an error"
Note that checking of reserved areas is optional and many (but not all)
devices do check those areas and will fail the operation if anything is
>From a future definition point of view it is much better to fail when a
reserved area has a non-zero value. If it does not fail then the issuing
device will think something is happening that is not and that can lead to
unpredictable results.
Future definitions that would define a reserved area will also define the
zero value be equal to the legacy operation, that maintains backward
Bye for now,
George Penokie
LSI Corporation
3033 41st St. NW
Suite 100
Rochester, MN 55901
george.penokie at lsi.com
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Stephen Finch
Sent: Monday, July 25, 2011 11:43 AM
To: t10 at t10.org
Subject: Re: 11-036r9 Reserved Bits in TTIU
In the past, we have stated that reserved bits are set to zero and ignored by
the receiver.  This is to limit the checking by the receiver, but more
importantly, to allow these fields to be used in future generations of a
In 11-036 (approved for SPL-2), the reserved bits in the TTIU must be checked
and, if non-zero, cause an error response to be sent.  This seems to be
inconsistent with past usage of "reserved" and will limit future versions of
this standard if additional bits of the TTIU are needed.
I submit that we should remove the checking of these reserved bits.
Stephen Finch
720 864-4751
720 883-1414 (cell)
Western Digital, Longmont

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