TPTT setting for multiple XFER_RDY by a WRITE command

Craig Stoops craig at expertio.com
Tue Jun 16 09:36:00 PDT 2009


* From the T10 Reflector (t10 at t10.org), posted by:
* "Craig Stoops" <craig at expertio.com>
*
Hi Wooseok,
The use by a target of a TTPT is optional. If not used, the TTPT should be
set to FFFF
The purpose of the TTPT is to allow a target port DMA hardware a unqiue
context "handle" to associate incoming write data that is in response to a
XFER_RDY, and thus to a given set of DMA buffers. Not all hardware designs
use this type of system.
The only requirements of your target if your hardware does use the TTPT is
that it be set to a unique value on every outstanding XFER_RDY.
Initiators then will reflect the TTPT received in the XFER_RDY in any
associated write data frames for that xfer_rdy.
Section 9.2.1 of the SAS spec covers this subject.
Hope this helps.
Craig Stoops
ExpertIO, Inc - The leading provider of SAS, SATA and Fibre Channel
Verification IP and Consulting Services.
www.expertio.com 
-----Original Message-----
From: Wooseok Chang [mailto:wooseokc at gmail.com] 
Sent: Monday, June 15, 2009 11:51 PM
To: t10 at t10.org
Subject: TPTT setting for multiple XFER_RDY by a WRITE command
* From the T10 Reflector (t10 at t10.org), posted by:
* Wooseok Chang <wooseokc at gmail.com>
*
Hello,
I was looking for who I could ask this kind of questions.
We are developing SAS target devices and found some description about TPTT
(Target Port Transfer Tag) in the SAS spec is somewhat ambiguous. When the
target sends multiple XFER_RDY's for a WRITE command to transfer multiple
series of DATA frames, is the target supposed to set the TPTT value in each
XFER_RDY frame with a different value, or the same value, or don't care? I
think the DATA frames are all in the same context conceptually, but the spec
sounds like we may need to fill the TPTT field with another value . Please,
let me know what the spec means, or where to contact to ask such a SAS
protocol question.
Thank you.
WS
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