SAS error recovery use case - Device Server detected Data Offset Error

Seto, Pak-lung pak-lung.seto at intel.com
Wed Jul 12 05:27:24 PDT 2006


Formatted message: <A HREF="r0607122_f.htm">HTML-formatted message</A>

________________________________
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of George
Penokie
Sent: Thursday, July 06, 2006 3:44 PM
To: Larry Chen
Cc: t10 at t10.org
Subject: Re: SAS error recovery use case - Device Server detected Data
Offset Error
Larry, 
The answers to your questions are as follows: 
1 - Under normal operations an SSP_RESPONSE can be sent in the same
connection, but it is not possible to do that if there is a error
detected at the link layer. 
[Seto] But Data Offset Error is not a link layer error, it is a
Transport Layer error, right?
That's because any of the errors you are asking about cause the
connection to be closed by the link layer. So the answer to your
specific error case in no a new connection is required to transmit the
SSP_RESPONSE.
[Seto] Don't see why it needs a new connection to transmit SSP_RESPONSE.
2- This cannot happen as the connection is automatically closed when an
ACK/NAK timeout occurs. 
[Seto] I thought Larry's is questioning about - SSP_RESPONSE is received
before ACK/NAK timeout?
3- Effectively yes. All the SSP state machines stop running when either
the Request Close message or the Request Break message is sent by the
SSP_D state and do not start up again until an Enable Disable SSP
message is received. 
4- The only two timers that overlap are the ACK/NAK Timeout timer and
the Credit Timeout timer. Both of those timers can cause an action by
the SSP_TF2Tx_Wait state. The description on the priority is in section
7.16.8.6.3.3 Transition SSP_TF2:Tx_Wait to SSP_TF4:Transmit_DONE.
Basically the ACK/NAK Timeout timer has priority over the Credit Timeout
timer. 
The DONE timeout timer is only relevant after a Transmitted DONE message
is received by the SSP_D state at which time no other link layer timer
is relevant. 
The other link layer timers are: 
The Open Timeout timer - That timer is only used when the SL_CC state
machine is in the SL_CC!:ArbSel state. It is initialized on entry and
control is completely defined within that state. 
The Close Timeout timer - That timer is only used when the SL_CC state
machine is in the SL_CC4:DisconnectWait state. It is initialized on
entry and control is completely defined within that state. 
The Break Timeout timer - That timer is only used when the SL_CC state
machine is in the SL_CC5:BreakWait state. It is initialized on entry and
control is completely defined within that state. 
Bye for now,
George Penokie
Dept 9A8 030-3 A410
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208 
Larry Chen <Larry_Chen at pmc-sierra.com> 
Sent by: owner-t10 at t10.org 
06/29/2006 07:07 PM 
To
"T10 (t10 at t10.org)" <t10 at t10.org> 
cc
Subject
SAS error recovery use case - Device Server detected Data Offset
Error
Hi, 
I have an SAS error recovery use case which can not 
Solve by myself after reading the SAS-1.1 specification Rev 9e. 
The use case scenario starts when the Device Server detects 
A Data Offset Error (assume that the first of two data 
Frames is dropped/lost) during a Write command. 
As stated in the spec, the Device Server sets the appropriate 
SCSI error message in the SSP_RESPONSE frame and sends 
It to the initiator. 
Ex) 
Initiator						   Target 
---------------SSP_Command(WRITE)--------------> 
<-------------------------------ACK------------------------- 
<------------------------------SSP_XFR_RDY---------- 
---------------------------------ACK-------------------------> 
--------------SSP_DATA-1---------------> DROPPED/LOST 
--------------SSP-DATA-2-------------------------------->      Data
Offset Error is detected 
<--------------------------------ACK-2----------------------- 
<-------------SSP_RESPONSE(DATA_OFFSET_ERROR) 
QUESTION-1: Can SSP_RESPONSE be sent in the same connection 
Or does it need to open a new connection? 
QUESTION-2: If SSP_RESPONSE is received when ACK-TOV is still 
Running, is the ACK_TOV timer supposed to be cancelled? If so, can
someone 
Refer me to the place in the SAS spec where this is mentioned. 
QUESTION-3: Does closing a connection force cancelling of all 
Active timers, such as, ACK_TOV timer? 
QUESTION-4: does SAS spec mention about how ACK_TOV, 
DONE_TOV, AND BREAK_TOV timers interact e.g. priority, preemption? 



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