[T10] Clarification requested for the detection of scrambled DWORDS in Train-TX Speed Negotiation window

Tim Symons tim.symons at microsemi.com
Tue Jan 17 15:22:28 PST 2017


Lana,

Thank you for your enquiry about TTIU patterns. As a short response your "Understanding 2" is correct.



Here are a few references to help you reconcile this:

All my references will use SPL4r11 as this is the latest published version of the standard.



The Transmitter Training Information Unit (TTIU) (See  5.10.1) is a 4-byte unit that is transmitted using BMC (See  5.9). Each bit of the TTIU is transmitted 10 bits wide (i.e. 1/10th SAS rate) using BMC and is not scrambled.

TTIU detection is described in the following sections depending on the mode of transmitter operation:

*        5.11.4.2.3.4.4 Pattern marker detection while in SAS dword mode

*        5.11.4.2.3.4.5 Pattern marker detection while in SAS packet mode



>From your enquiry I get the impression that you are trying to decode the scrambled training data. This is not necessary.



During the Transmitter training process there is no requirement for the receiver to decode the scrambled training data as there are no error conditions or events that use that data or if the pattern is incorrect.

The purpose of the scrambled training data is to allow the analog receiver to tune its settings in response to the tuned transmitted signal.

The scrambled train pattern provides a good frequency spectral content to optimize tuning the received signal eye, and to provide feedback for the next transmitter tuning request TTIU.



When both receivers in a link report TRAIN_COMP then that training window is complete.



Regards

Tim Symons

SPL editor.



Tim.Symons at microsemi.com


From: t10-bounces at t10.org [mailto:t10-bounces at t10.org] On Behalf Of Lana Chan
Sent: Tuesday, January 17, 2017 11:30 AM
To: t10 at t10.org
Subject: [T10] Clarification requested for the detection of scrambled DWORDS in Train-TX Speed Negotiation window

EXTERNAL EMAIL
Hello,

We have a query regarding Scrambling in Train-Tx Speed Negotiation Window in Physical Layer in which the  Train-Tx comprises of exchange of Transmitter Training Pattern between two SAS devices.

Per the Working Draft SAS Protocol Layer - 4 (SPL-4), T10/BSR INCITS 538 Revision 08a, Section - 5.11.4.2.3.4.1 Phy's transmitter initial condition,  the transmitter training pattern comprises of the following

[cid:image001.png at 01D219A9.4CFF68A0]


Can you please provide clarification for the following scenario:

1.      Receiver does not detect 1st pattern marker. So the 1st TTIU will be missed along with 1st set of 58 scrambled dwords.

2.      Receiver detects 2nd pattern marker and also detects 2nd TTIU pattern.

We see two possible understandings:

Understanding 1 : Receiver tries to detect 58 dwords and tries to descramble them.
Here it will not be able to detect those 58 scrambled dwords because receiver will try to descramble data dwords using
initial seed(As it has missed initial Transmitter Training Pattern) whereas transmitter would send scramble dwords using
a new seed. Based on this understanding receiver will not be able to detect any of the of Transmitter Training Pattern.
And Train Tx will be unsuccessful.

Understanding 2 : Receiver shall ignore the detection of 58 scrambled dwords.
Here if the receiver ignore those 58 dwords then there is no question of descrambling
Dwords. Hence Train-Tx SNW will be successfully detected.

The specification also indicates the following :
The scrambler is the same as that defined for the link layer (see 6.8) and shall be initialized at the end of
RateChangeDelayTime. The scrambler shall not be reinitialized for the remainder of the Train_Tx-SNW. (Reference -Working Draft SAS Protocol Layer - 4 (SPL-4),
T10/BSR INCITS 538 Revision 08a, Section - 5.11.4.2.3.4.1 Phy's transmitter initial condition)

RateChangeDelayTime(RCDT) is the time for which transmitter drives idle at the beginning of Train-Tx SNW before
Transmitting any data.

Can you please provide us clarification as to whether or not we should be following scenario two or otherwise.

Kind Regards
Lana




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Lana May Chan   |   Senior Product Marketing Manager, Verification IP

P: 4084285749   M: 4086236108   www.cadence.com<http://www.cadence.com>








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