FW: DONE in response to CREDIT_BLOCKED

Sachidanandam, Kannan Kannan_Sachidanandam at maxtor.com
Sun May 4 08:55:41 PDT 2003

* From the T10 Reflector (t10 at t10.org), posted by:
* "Sachidanandam, Kannan" <Kannan_Sachidanandam at maxtor.com>
Just forwarding a message. This is a discussion on CREDIT blocked that I did
not see on t10.

-----Original Message-----
From: Evans, Mark 
Sent: Tuesday, April 29, 2003 5:07 PM
To: Rob Elliott (E-mail); Leshay, Bruce; George Penokie (E-mail);
Sachidanandam, Kannan
Subject: DONE in response to CREDIT_BLOCKED

Hello all,

Rob wrote:

"I agree that in the current standard the recipient does not handle DONE
(NORMAL) and DONE (CREDIT TIMEOUT) any differently.

If a phy receives DONE (CREDIT TIMEOUT) as a result of it sending
CREDIT_BLOCKED, it is particularly uninformative since the phy knows it sent

DONE (CREDIT TIMEOUT) for RRDY timeouts might be helpful for diagnosing
problems - if a phy is never giving RRDYs this highlights the reason that a
connection is opened and closed.

If it were not used for CREDIT_BLOCKED replies, an analyzer triggering on
DONE (CREDIT TIMEOUT) would trigger on definite errors.  Since we allow this
in reply to CREDIT_BLOCKED, it's less useful for that purpose."

I agree with all of the above.  In addition, there is another facet that
makes DONE (CREDIT TIMEOUT) less useful (useless, even):  I think that it's
impossible to test which DONE a device sends in response to a
CREDIT_BLOCKED.  If a device receives a CREDIT_BLOCKED as seen on the wire,
then that particular implementation sends a DONE (NORMAL), there is no way
to tell if the DONE (NORMAL) was sent in response to the CREDIT_BLOCKED, or
because the device is actually done - regardless of the time between when a
CREDIT_BLOCKED is seen on the wire and a DONE (either flavor) is seen on the

If, ultimately, no one sees any usefulness in DONE (CREDIT TIMEOUT), we
could adjust the standard accordingly.  In the meantime, we could leave the
standard as it is, but I think we could add a note something like, "If a
device sends a CREDIT_BLOCKED, then it may receive either a DONE (CREDIT

Please feel free to call or send an email to me with your comments about
this stuff.


Mark Evans
Maxtor Corporation
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