UAS IU Query

Madhukar madhukar.gubba at
Thu Jun 4 04:12:37 PDT 2009

* From the T10 Reflector (t10 at, posted by:
* Madhukar <madhukar.gubba at>
Hello All,
I'm working on UAS device for which a driver is being developed in
Linux platform. I have few questions regarding Information Units
available in UAS spec.
1. The old BOT protocol has Command Block Wrapper (CBW) packets which
holds datatransferlength and flags fields. I do not see any thing
similar in Command Information Unit or any other IU. How does the
target port know what is the length of data that is in process?
Also, does target port need to be aware of data direction. My
assumption regarding data direction is that since target port has
separate end points for command and data, the target port need to be
ready on two endpoints on separate threads to receive either data or
2. How do i categorize that an incoming SCSI command in non-data or
data command. My assumption is that, if the datatransferlength is
greater than zero, then it is a data command else it is a non-data
command. Does this make sense?
Any help is much appreciated. Pardon me if my questions sound silly. :)
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