Mike Berhan mikeb at
Fri May 16 08:09:44 PDT 2008

* From the T10 Reflector (t10 at, posted by:
* "Mike Berhan" <mikeb at>
When I originally posted my message, I had assumed there was well defined
sense data expected but this appears to be somewhat open to interpretation
(which would explain the different behavior I see with various SPC-3 devices
I have tested against).
There should be only one consistent response to an unsupported opcode /
service action and I think SPC should be explicit on this.  There are there
possible options as I see it:
1.)  Device returns 20 00 (INVALID COMMAND OPERATION CODE)
2.)  Device returns 24 00 (INVALID FIELD IN CDB)
3.)  Device returns a new sense data 20 XX (INVALID SERVICE ACTION)
I would put #2 as my least preferred option though I understand the
historical points that Rob makes.  Let's use an example.  If I send a Report
Supported Operation Codes and the device returns 24 00, what is the device
telling me?  Is it telling me that it doesn't support the command or is it
telling me that it does support the command, but not some field in the CDB.
Perhaps I set a reserved bit or set some field to a value it doesn't
support.  If the device doesn't return sense key specific data (which a
number of devices do not), then I don't know what field it does not like.
Is it the Service Action or some other field?  I would then need to turn to
the specification to determine if the command is supported or not.
tell the host software very specifically that the command is simply not
A new sense data 20 XX (INVALID SERVICE ACTION) seems to be the best option
though I'm not too keen on introducing new sense data.	My main goal is to
have this clearly defined in SPC so that, as I work with various target
vendors, I can help them ensure they are returning expected sense data.
Mike Berhan
busTRACE Technologies
9700 Village Center Drive
Suite 50-F
Granite Bay, CA  95746
916.773.4554 phone
916.218.6283 fax
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