Credit Advance Question

Penokie, George George.Penokie at lsi.com
Mon Apr 21 07:59:06 PDT 2014


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Judy,
It looks to me like there is an error in the description in section
6.16.4.3.4 Transition SL_CC1:ArbSel to SL_CC3:Connected. This transition only
occurs when arbitration is won by the phy. When arbitration is won and open
address frames cross the information in the losing open address frame is
discarded. So the following statement in section 6.16.4.3.4 Transition
SL_CC1:ArbSel to SL_CC3:Connected is in error:
If credit advance is implemented (see 4.1.14) and:
a) the CREDIT ADVANCE bit is set to one in the received OPEN address frame;
and
b) the SAS PROTOCOL field is set to 001b (i.e., SSP) in the received OPEN
address frame,
then this transition shall include an Advance Credit argument.
It should be deleted or restated as follows:
If credit advance is implemented (see 4.1.14) and:
a) the CREDIT ADVANCE bit is set to one in the << transmitted >>  OPEN
address frame; and
b) the SAS PROTOCOL field is set to 001b (i.e., SSP) in the << transmitted >>
OPEN address frame,
then this transition shall include an Advance Credit argument.
Tim,
What was your intent? Did you want the advance credit on both sends of the
connection or did you want the advance credit only on the side that accepted
the connection.
Bye for now,
George Penokie
LSI Corporation
3033 41 St NW
Rochester , MN 55901
507-328-9017
george.penokie at lsi.com
From: Judy Westby [mailto:judy.westby at seagate.com]
Sent: Friday, April 18, 2014 4:31 PM
To: Penokie, George; Tim.Symons at pmcs.com; Gerry Houlder
Subject: Credit Advance Question
We were looking at the credit advance function and wanted to clarify
something.
The following is included in the Transition SL_CC0:Idle to SL_CC2:Selected,
Transition SL_CC1:ArbSel to SL_CC3:Connected, and Transition SL_CC1:ArbSel to
SL_CC3:Connected:
If credit advance is implemented (see 4.1.14) and:
a) the CREDIT ADVANCE bit is set to one in the received OPEN address frame;
and
b) the SAS PROTOCOL field is set to 001b (i.e., SSP) in the received OPEN
address frame, then this transition shall include an Advance Credit argument.
When Open Address frames are sent by both sides at about the same time, one
will win and receive OPEN_ACCEPT and one will lose and send OPEN_ACCEPT.  The
Advance Credit argument may be set for both at the same time.  Both
 could then transmit a frame before receiving the first RRY.
We didn't see any issues with this but 13-138 mentioned the OPEN_ACCEPT so
just wanted to confirm that the intent wasn't that it is dependent on which
port wins.
--
Judy Westby
Seagate Technology
952-402-2719
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