SCSI Tagged Commands Question
Gary_Peterson at DGC.ceo.dg.com
Gary_Peterson at DGC.ceo.dg.com
Mon Mar 6 07:18:01 PST 1995
CEO comments:
Attached.
Please respond to: Gary_Peterson at DGC.ceo.dg.com
Thanks.
CEO document contents:
To: John Lohmeyer
CC: SCSI Reflector
From: Gary S. Peterson Gary_Peterson at DGC.ceo.dg.com
Data General Corp.
Re: SCSI-2/SCSI-3 Overlapped Tagged Command Handling
Date: March 1, 1995
We have a question regarding the proper handling of overlapped tagged
commands to a disk drive. According to the SCSI-2 spec, the drive should treat
an attempt to reissue an in-use tag as an Incorrect Initiator Connection,
clearing the tagged command queue and returning a ABORTED COMMAND/OVERLAPPED
COMMANDS ATTEMPTED, as per 7.5.2.
However, consider the following:
Select w/ATN (7,0)
Message Out /C0 20 0C (Tag)
Command /2A 00 00 2E 0B E9 00 00 3D 00
Message In /04 (Disconnect)
Bus Free
Select w/ATN (7,0)
Message Out /C0 20 0C (Tag)
Command /2A 00 00 2E 0B E9 00 00 3D 00
Message In /04 (Disconnect)
Bus Free
Select w/ATN (7,0)
Message Out /C0 20 0E (Tag)
Command /2A 00 00 32 F6 52 00 00 16 00
Message In /04 (Disconnect)
Bus Free
Reselect (0,7)
Message In /80 20 0C (Tag)
Status /02 (Check Condition)
Message In /00
Select w/ATN (7,0)
Message Out /C0 01 03 01 19 08 (Identify, SDTR)
Message In /01 03 01 19 08 (SDTR)
Command /03 00 00 00 12 00
Data In /70 00 0B 00 00 00 00 0A 00 00 00 00 4E 00 01 00 00 00
Status /00
Message In /00
Bus Free
Reselect (0,7)
Message In /80 20 0E (Tag)
.
.
.
Our questions:
1. What is supposed to happen with the Tag 0E command? That is, when the
drive clears its queue, is it when it detects the error (parsing the
second 0C command) or when it reports the check condition (after
receiving the 0E command)?
2. According to the SCSI-2 spec, "if a target receives a queue tag that is
currently in use for the I_T_L nexus, it shall respond as defined in
7.5.2". (section 6.6.17).
Does this imply that a target is responsible for validating the tag ID
before disconnecting, to prevent the condition described above?
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