SPC Inquiry for Quad-Aligned Zero -- deprecated since SPC-4 maybe

plavarre at lexar.com plavarre at lexar.com
Thu Jan 3 11:31:58 PST 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* <plavarre at lexar.com>
*
Ralph,
> Mark,
I take the liberty of adding my answer in parallel ...
> What is wrong with TEST UNIT READY as a way to validate Command Out
and Status In processing?
Yes much of the time TEST UNIT READY exercises Command Out and Status In
without Data.
Specifically this works any time media happens to be present in the
logical unit and happens to be readable and happens to have no unit
attentions pending for it.
TEST UNIT READY disrupts the bus violently otherwise -- the first
trouble is CHECK CONDITION, and then all the consequences that may
follow, e.g., some SCSI transports that follow up CHECK CONDITION with
REQUEST SENSE, such as USB and FireWire and ATAPI. The REQUEST SENSE
requires Data processing to move the sense data, which implies arcane
complexities like negotiated data rates and recovering from
non-quad-aligned REQUEST SENSE allocation lengths like the 12h (18)
popular in Windows bus traces.
All the same, INQUIRY for zero is less common than TEST UNIT READY. So
arguably the host should use TEST UNIT READY to exercise Command Out and
Status In, except when the device may be exercising the option of
removable media.
*
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at t10.org



More information about the T10 mailing list