Few questions in Rev.03e SAS

Chris.Malakapalli at seagate.com Chris.Malakapalli at seagate.com
Mon Mar 24 14:58:33 PST 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* Chris.Malakapalli at seagate.com
*
Hello,

I have a related question to Q2 below.

Currently, a CREDIT_BLOCKED primitive from the receiver will lead to the
transmitter sending a DONE (Credit Timeout). This is the same response for
not receiving an ACK or NAK within the 1ms period. It appears to me that we
lose valuable information by lumping the two into one category of DONE
(Credit Timeout). In the CREDIT_BLOCKED case, the resources are definitely
not available to receive the frame but in the Credit Timeout case,
resources are available but RRDY is either lost or not received by the
transmitter in time. Wouldn't the implementors want to be able to
differentiate between the two, especially when interoperability comes into
play for SAS? Am I missing something?

Also, it appears that in most cases the time period of 1ms is the same for
both transmitter and receiver. I am wondering if this would leave a small
window for a problem. Take the above case for example. If the receiver did
send RRDY within 1ms, i.e, say (1-t) ms before the timer expires (t being a
small fraction of a millisecond), and it took RRDY more than (t)ms to reach
the destination port and for SSP_TF2 state machine to detect Tx Credit
Status (Credit Available), then we have a Credit Timeout condition. In this
case, who is at fault? the source port? destinator port? or something else,
like expander port?

There are other 1ms timeout scenarios like this in the specification.

Thanks for your response.

-Chris


----- Forwarded by Chris Malakapalli/Seagate on 03/24/2003 04:21 PM -----
                                                                                                                                         
                      Chris.Malakapalli@                                                                                                 
                      seagate.com                To:      t10 at t10.org                                                                    
                      Sent by:                   cc:                                                                                     
                      owner-t10 at t10.org          Subject: Re: Few questions in Rev.03e SAS                                               
                      952-402-3441                                                                                                       
                                                                                                                                         
                      03/21/2003 11:02                                                                                                   
                      AM                                                                                                                 
                                                                                                                                         
                                                                                                                                         




* From the T10 Reflector (t10 at t10.org), posted by:
* Chris.Malakapalli at seagate.com
*

Reading carefully the second time, I may have found the answer to Q1. The
Frame Transmitted message is coming from SSP Transmitter as shown in Figure
96. Perhaps, item a could be revised (when convenient) as "receiving a
Frame Transmitted message from the SSP Transmitter".





                      Chris

                      Malakapalli              To:      t10 at t10.org

                      952-402-3441             cc:      (bcc: Chris
Malakapalli/Seagate)
                                               Subject: Few questions in
Rev.03e SAS
                      03/21/2003 10:51

                      AM






Hello,

Few questions in section 07 of rev.03e SAS specification.

Q1) Section 7.16.7.6.4.2 states:

"Transition SSP_TF3:Indicate_Frame_Tx to SSP_TF1:Connected_Idle

This transition shall occur after:
a) receiving a Frame Transmitted message;
b) sending an Frame Transmitted message to the SSP_TIM state machine; and
c) sending a Frame Transmitted confirmation to the port layer"

The "Indicate_Frame_Tx" or SSP_TF3 does not receive a Frame Transmitted
message according to the depiction in Figure 94. What is item a above
referring to or is this an error?

Q2) Section 7.16.7.6.3.3 states

"Transition SSP_TF2:Tx_Wait to SSP_TF4:Indicate_DONE_Tx

This transition shall occur and include a Credit Timeout argument if this
state was entered from the
SSP_TF1:Connected_Idle state with a Transmit Frame Balance Required
argument or a Transmit Frame
Balance Not Required argument and the last Tx Credit Status message
received had an argument of Blocked.

Shouldn't the transition argument above be "Credit Blocked" instead of
"Credit Timeout"?

Q3) Section 7.16.7.6.3.3 states

"Transition SSP_TF2:Tx_Wait to SSP_TF4:Indicate_DONE_Tx

This transition shall occur and include a Credit Timeout argument if:
a) this state was entered from the SSP_TF1:Connected_Idle state with a
Transmit Frame Balance
Required argument or a Transmit Frame Balance Not Required argument;
b) the Credit Timeout timer expires before a Tx Credit Status (Available)
message is received; and
c) the last Tx Balance Status message received had an argument of Balanced,
or a Tx Balance Status
(Balanced) message is received before a ACK/NAK Timeout message is
received"

Shouldn't there an "and" at the end of item a above?

Thanks in advance for your responses.

-Chris




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