Unit Attention and queued commands

Charles Monia Monia at mail.dec.com
Fri May 16 10:51:59 PDT 1997


* From the SCSI Reflector (scsi at symbios.com), posted by:
* Charles Monia <Monia at mail.dec.com>
*
----------
From: 	=
ljr at austin.ibm.com[SMTP:"\"ljr at austin.ibm.com\""@SHDNS1.STARCH.MRGATE.SHR=
MSG.SHR.mts.dec.com]
Sent: 	Thursday, May 15, 1997 6:43 PM
To: 	monia at am.SHRMSG.SHR.mts.dec.com
Subject: 	Unit Attention and queued commands

<<File: ATT18323.txt>>
* From the SCSI Reflector (scsi at symbios.com), posted by:
* ljr at austin.ibm.com (Les Record)
*



Assume we have a SCSI-2 target with QERR=3D0 (Mode page 0A), and we get =
the
following sequence:

1 SCSI RESET
2   TAG 1 - COMMAND - disconnect
3   TAG 2 - COMMAND - disconnect
4   TAG 3 - COMMAND - disconnect
5   TAG X - STATUS=3DCheck - COMPLETE
6   UNTAG - COMMAND=3DRequest Sense - DATA=3DSense Data - STATUS=3DGood =
- COMPLETE
7   ????

What should happen to the commands queued prior to the CAC generation at =
line
5, since they were received while a Unit Attention exists (due to the =
reset)
but prior to the generation of the CAC?  The standard says (section 7.9,
paragraph 7):


"If an initiator issues a command other than INQUIRY or REQUEST SENSE =
while a
unit attention condition exists for that initiator (prior to generating =
the
contingent allegiance condition for the unit attention condition), the =
target
shall not perform the command and shall report CHECK CONDITION =
status..."

My opinion only:

The Logical Unit should have reported the pending UNIT ATTENTION by =
returning a CHECK CONDITION on the command issued in step 2 after the =
SCSI RESET.  Otherwise, as you imply, clearing the CA at step 6 will =
allow commands issued in 2, 3 and 4 to complete without reporting the =
CHECK CONDITION as specified in the paragraph you quote.

In other words, the scenario you describe should never have been allowed =
to happen.

Charles

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* Charles Monia                           *
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