SAS-2: A question on SSP Link Layer Protocol

Sheffield, Robert L robert.l.sheffield at intel.com
Fri Sep 8 15:24:08 PDT 2006


* From the T10 Reflector (t10 at t10.org), posted by:
* "Sheffield, Robert L" <robert.l.sheffield at intel.com>
*
Actually, I've been confused about this as well. I certainly understand
the meaning of ACK/NAK balance for transmitted frames, but it really
doesn't make sense to me for received frames. Seems the first thing the
SSP_RF state machine does when it receives a frame is transmit an ACK
for that frame. Once that's happened, why would there ever be an
imbalance? Isn't it just a design choice as to whether to send the ACK
first or to signal receipt of the frame first? Wouldn't the choice be
the same always?
Bob Sheffield
Intel 
-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Day,
Brian
Sent: Friday, September 08, 2006 2:17 PM
To: Stephen FINCH; T10 Reflector
Subject: RE: SAS-2: A question on SSP Link Layer Protocol
* From the T10 Reflector (t10 at t10.org), posted by:
* "Day, Brian" <Brian.Day at lsil.com>
*
Steve...
That would happen during non-interlocked DATA frames.  For example, the
link could receive 2 DATA frames back-to-back before any ACK/NAKs are
ever transmitted.
That should never happen when receiving interlocked frames though...
which is what the transport layer is checking for in section 9.2.6.2.2.3
in the ST_IFR state.
Brian Day
LSI Logic
-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Stephen
FINCH
Sent: Friday, September 08, 2006 9:54 AM
To: T10 Reflector
Subject: SAS-2: A question on SSP Link Layer Protocol
* From the T10 Reflector (t10 at t10.org), posted by:
* Stephen FINCH <steve.finch at st.com>
*
In section 7.16.8.7 SSP_RF (receive frame control) state machine, in the
last paragraph and its bullet items it states:
"
	A) if the last Rx Balance Status message received had an
argument of Balanced, send a Frame Received (ACK/NAK Balanced)
confirmation to the port layer; or
	B) if the last Rx Balance Status message received had an
argument of Not Balanced, send a Frame Received (ACK/NAK Not Balanced)
confirmation to the port layer.
"
Since ACKs and NAKs can be sent at any where within an SSP connection
including within a frame being transmitted, can anyone provide an
example of when case B will ever occur?  I.e., after receiving a frame
the ACK or NAK of the previous frame has not been sent?
Am I missing something?
Steve Finch
STMicroelectronics
303 381-3587
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