Revision 1 of document accepted for Automatic Clear ACA
Bob.Snively at eng.sun.com
Mon Sep 19 21:31:05 PDT 1994
X3T10/94-189, revision 1
From: Bob Snively
Sun Microsystems Computer Company
Mail Stop UMPK 12-302
2550 Garcia Ave,
Date: September 14, 1994
Subject: Proposed solution for Automatic Clear of ACA
SAM Revision 15 indicates in section 6.1.2, page 45 that,
All logical units shall implement support for at
least one of the ACA bit values and may support both values.
This proposal describes a protocol and
proposes wording to include that wording in SAM and SPC.
The assumptions of this proposal are:
a) The proposal should be compatible with SCSI-2
initiators and targets.
b) The proposal should allow each command to be
marked as to whether or not a Check
Condition for that command will establish an
Automatic Contingent Allegiance (ACA) condition.
The control objects used by this protocol are described in the
Object name Location Description, relevant values
ANSI-approved Version INQUIRY data, Specified in SPC
byte 2, bits 2-0 Indicates implemented versio
2h = SCSI-2 compliant
3h = SCSI-3 compliant
Normal ACA Supported INQUIRY data, Specified in SPC
location tbd Indicates Normal ACA supported by target
0b = ACA Autoclear only
1b = Normal ACA or ACA Autoclear
Normal ACA CDB Control Field, Specified in SAM
bit 3 Indicates Normal ACA required if
CHECK CONDITION occurs
0b = ACA Autoclear if check
1b = Normal ACA if check
The following behaviors are expected of targets when they indicate the
following combinations of bits.
Normal ACA Supported = 0 Normal ACA Supported = 1
ANSI-approved Version = SCSI-2 SCSI-2 Contingent Allegiance Not allowed
ANSI-approved Version = SCSI-3 Only Normal ACA = 0 allowed: For Normal ACA = 0:
Autoclear if check Autoclear if check
For Normal ACA = 1:
Normal ACA if check
If the target identifies itself as a SCSI-2 target, it
cannot identify itself as supporting normal ACA.
SCSI-2 devices support Contingent Allegiance or Extended
Contingent Allegiance as defined in the
If the target identifies itself as a SCSI-3 target, it can
identify itself as supporting autoclear only or as
supporting both normal ACA and autoclear.
If a SCSI-3 target supports autoclear only, the initiator
shall not transmit commands that contain the
Normal ACA bit set to the Normal ACA (1) state. If a
command with the Normal ACA bit is transmitted
to a target, the target will indicate with a CHECK CONDITION
that the control field is invalid.
If a SCSI-3 target supports autoclear only, any command
that ends with a CHECK CONDITION or
COMMAND TERMINATED status establishes an Automatic Contingent
Allegiance condition. If the
link protocol for that target performs autosense, the
ACA condition is cleared automatically upon
completion of the autosense operation. If the link
protocol for that target does not perform autosense, the
ACA condition is cleared according to the rules for
SCSI-2 Contingent Allegiance.
If a SCSI-3 target supports both normal ACA and
autoclear, the behavior of the target when a CHECK
CONDITION or COMMAND TERMINATED status occurs
depends upon the state of the Normal ACA
bit in the CDB of the failing command. If the
Normal ACA bit is set to zero, the target establishes an
ACA condition. If the link protocol for that target
performs autosense, the ACA condition is cleared
automatically upon completion of the autosense
operation. If the link protocol for that target does not
perform autosense, the ACA condition is cleared
according to the rules for SCSI-2 Contingent Allegiance.
If the Normal ACA bit is set to one, the target
establishes an ACA condition. The ACA condition
remains until cleared according to the rules
specified in SAM, section 184.108.40.206.
To specify this behavior in the standards, the following
words must be modified and added to the
Changes required for SPC:
The ANSI-approved Version field is already correctly
described in section 7.5.1, Table 22, and associated
The following text is proposed to be added to
section 7.5.1. The Normal ACA Supported bit should be
added to the proper field in the INQUIRY data format
chart, to be determined. An appropriate
abbreviation is NormACA. The text would then be added
after the text describing the RelAddr bit.
The Normal ACA Supported bit (NormACA) of one
indicates that the device server supports
both the Normal ACA and the ACA Autoclear
function. A NormACA bit of zero indicates that
the device server does not support Normal ACA,
but does support the ACA Autoclear function.
Changes required for SAM:
The bit presently named ACA is renamed Normal ACA
or NACA at all referenced locations.
The following text is removed:
All logical units shall implement support for
at least one of the ACA bit values and may support
and replaced with the following text:
All logical units shall implement support for
the Normal ACA value of zero and may support the
Normal ACA value of one. The ability to support
a Normal ACA value of one is indicated in
standard INQUIRY data.
Sections 6.6.1, 220.127.116.11 are unchanged.
The following text in paragraph 3 is deleted:
If the logical unit accepts a value of zero for the ACA bit
The first sentence will then read:
If the NACA bit is set to zero in the CDB control
byte of the faulting command, then the SCSI-2
rules for clearing auto contingent allegiance
condition shall apply.
No other changes should be required.
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