Multiple Commands in UAS

Curtis Stevens curtis.stevens at
Mon Aug 10 17:11:28 PDT 2009

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Mark, both the Sense IU and the Read Ready IU are returned from the device
on the same pipe.  You have to complete the sending of the Sense IU and wait
for USB-2 to give you an IN request on the status pipe before you can send
the Read Ready IU.
Curtis E. Stevens
Sr. Staff  Engr - Standards & Features Technology
20511 Lake Forest Drive #A 113-F
Lake Forest, California 92630
Phone: 949-672-7933
Cell: 949-307-5050
E-Mail: Curtis.Stevens at  
From: Mark Overby [mailto:MOverby at] 
Sent: Monday, August 10, 2009 5:09 PM
To: Madhukar; Curtis Stevens
Cc: t10 at
Subject: Re: Multiple Commands in UAS
I disagree with your assertion. The method of reception of the SENSE IU is
independent of how you transmit the COMMAND IU on a separate pipe.
On 8/10/09 9:46 AM, "Madhukar" <madhukar.gubba at> wrote:
* From the T10 Reflector (t10 at, posted by:
* Madhukar <madhukar.gubba at>
On Mon, Aug 10, 2009 at 9:27 PM, Curtis Stevens<curtis.stevens at>
> You need to wait for the USB ACK on the status pipe before sending the
> Ready IU.  In USB-2, you will only be able to send the Read Ready IU in
> response to a request for the IU from the initiator port.
Thank You for the reply.
So, it means two requests cannot be processed at same point of time
|from two different threads on same pipe. The second request can only
be started when there is an ACK for the first request. The second
request need to wait for the completion of first one and start it at
later point of time.
Is this different in case of USB-3?
Thank You.
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