[T10] SAS Scrambling in Dword mode

Mohammed, Ahmed Ahmed_Mohammed at mentor.com
Sun Aug 26 02:28:33 PDT 2018


Hi Tim,

Thanks for your reply and the information as well.

I agree to your points and thanks for bringing that to the working group. It will be better to have that explicitly described for dword mode as well.

Thanks
Ahmed

From: Tim.Symons at microchip.com [mailto:Tim.Symons at microchip.com]
Sent: Friday, August 24, 2018 2:16 AM
To: Mohammed, Ahmed <Ahmed_Mohammed at mentor.com>; t10 at t10.org
Subject: RE: SAS Scrambling in Dword mode

Ahmed,
I concur that this is not explicitly descried in the specification, and I've spent some time reviewing old proposal documents to see if this was clearly stated anywhere. I'll bring this to the attention of the working group at the next meeting (September) to see if they recommend adding text to explicitly define this.

Historically, SAS dword mode pre-dates SAS packet mode by 10-12 years, and when SAS dword mode was the only encoding defined, it was implicitly obvious that SAS data dwords are the only dwords that advance the scrambler because:

     *   The scrambler exists at the link layer- not the phy layer as it does for packet mode
     *   The scrambler is initialized by SOF primitives (explicitly stated in 6.8.2)
     *   In dword mode, primitives - by definition - cannot be scrambled
     *   Deletable primitives can be inserted/deleted within frames by expanders, so it would not be workable to advance the scrambler for deletable primitives
     *   There would be no value added - other than confusion - by advancing the scrambler on non-deletable primitives inside frames (RRDY/ACK/NAK/etc.)
     *   Because of all of the above point, the only rational behavior was for the scrambler to be advanced only by data dwords


Regards
Tim.
(SPL-5 Editor)


Tim Symons | Storage Architect
Microsemi Corporation
8555 Baxter Place, Burnaby, BC V5A 4V7. Canada
Tel. 604 415 6000
Tim.Symons at microchip.com<mailto:Tim.Symons at microchip.com>

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http://www.microsemi.com/


Regards


From: t10-bounces at t10.org<mailto:t10-bounces at t10.org> <t10-bounces at t10.org<mailto:t10-bounces at t10.org>> On Behalf Of Mohammed, Ahmed
Sent: Monday, August 13, 2018 3:36 AM
To: T10 Reflector <t10 at t10.org<mailto:t10 at t10.org>>
Subject: [T10] SAS Scrambling in Dword mode

EXTERNAL EMAIL
Hi All,

I have a question about scrambling in SAS link layer. It is not stated in the Dword mode with the scrambler should be advanced for non-data dwords (primitives) or not. This is clear for the packet mode, but no stated in Dword mode.

Appreciating more information about this.

Thanks
Ahmed
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