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

George Penokie gop at us.ibm.com
Thu Jul 6 12:44:15 PDT 2006


Formatted message: <A HREF="r0607065_f.htm">HTML-formatted message</A>

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. 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.
2- This cannot happen as the connection is automatically closed when an 
ACK/NAK timeout occurs.
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)------------à
ß-----------------------------ACK-------------------------
ß----------------------------SSP_XFR_RDY----------
---------------------------------ACK-----------------------à
--------------SSP_DATA-1-------------à DROPPED/LOST
--------------SSP-DATA-2------------------------------à      Data Offset 
Error is detected
ß------------------------------ACK-2-----------------------
ß-----------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?



More information about the T10 mailing list