Subject: RE: sas2r04 section 6.8 SP state machine SATA port selector support question Date: Thu, 3 Aug 2006 17:07:07 -0700 From: "Sheffield, Robert L" <robert.l.sheffield@intel.com> To: "Chang, Neil" <neil.chang@intel.com>, "Duerk, Vicky P" <vicky.p.duerk@intel.com>, <t10@t10.org> X-Message-Number: 7137 Formatted message: HTML-formatted message Attachment #1: outlook.jpg Neal and Vicky, The COMWAKE_Received state machine variable addresses a timing issue that only applies to the SP0 and SP1 states. Detection of COMWAKE in the SP3 and SP4 states was added for a different reason. The COMWAKE_Received state machine variable was added by proposal 04-357r1 (http://www.t10.org/ftp/t10/document.04/04-357r1.pdf <http://www.t10.org/ftp/t10/document.04/04-357r1.pdf>; ), and addresses a condition resulting from the fact that the duration of the COMWAKE signal is much shorter than that of the COMINIT signal, and it is possible that a port selector can respond to a received COMINIT, and the SAS phy can detect the COMWAKE, even before it has completed transmission of the COMINIT, and following the transition SP0->SP1, SP1 would erroneously determine the port selector is no longer present, except for the COMWAKE_Received state machine variable which communicates prior detection of the COMWAKE detected message. Detection of COMWAKE was added to SP3 and SP4 to handle corner timing cases that don't necessarily follow the nominal flow. There are places in the SATA 2.5 specification of the Port Selector behavior that indicate a COMINIT received on the phy connected to the SATA device might cause a COMINIT to be transmitted on the selected phy attached to the host (granted, this is subject to interpretation). At the time the COMWAKE detected message text was added to the SP state machine (see 03-273r2: http://www.t10.org/ftp/t10/document.03/03-273r2.pdf), it was believed that a SATA port selector could, indeed, transmit COMWAKE while the SP state machine is in the SP3:OOB_AwaitCOMX state or in the SP4:OOB_COMSAS state. Whether this is the prevailing interpretation of the Port Selector state machine in SATA 2.5 or not, maintaining the capability to detect COMWAKE in these two states does not impede interoperability, and could, perhaps, facilitate interoperability. Here is one example where during normal operation, both the SATA device and the SAS phy experience an internal reset at roughly the same time. In this case, the SATA device wins the race, marginally, and (subject to interpretation of the Port Selector description in SATA 2.5) the COMINIT transmitted by the SATA device is "propogated" through the port selector to the selected SAS phy before the SAS phy completes transmission of it's COMINIT, but after the SAS phy has transitioned to the SP0:OOB_COMINIT state. Then, having both transmitted and received COMINIT in the SP0:OOB_COMINIT state, the SP state machine transitions to the SP4:OOB_COMSAS state, where it receives the COMWAKE transmitted by the port selector in response to the COMINIT transmitted by the SAS phy. The attached sequence diagram shows the interaction. Best regards, Bob ________________________________ From: owner-t10@t10.org [mailto:owner-t10@t10.org] On Behalf Of Chang, Neil Sent: Tuesday, August 01, 2006 9:49 AM To: Duerk, Vicky P; t10@t10.org Subject: RE: sas2r04 section 6.8 SP state machine SATA port selector support question Thanks to those who responded - it seems like the question was ambiguous. Per Serial ATA 2.5 specification Port Selector section, the behavior of presence of SATA Port Selector is to transmit COMWAKE before transmit COMINIT from the port selector. It is clear that an attached SATA Port Selector can be determined if received COMWAKE before receiving COMINIT which is what described in the SP0:OOB_COMINIT state and the SP1:OOB_AwaitCOMX state. SP4:OOB_COMSAS may be entered after detected and transmitted COMINIT. Therefore, can a SATA Port Selector be determined in SP4 when receiving COMWAKE? As it's pointed out, similar question applies to SP3:OOB_AwaitCOMINIT_Sent state where it has received COMINIT already. Regards, Neil Chang ________________________________ From: Duerk, Vicky P Sent: Monday, July 31, 2006 11:06 PM To: Chang, Neil; t10@t10.org Subject: RE: sas2r04 section 6.8 SP state machine SATA port selector support question Neil, COMWAKE_Received state machine variable indicates "whether a COMWAKE detected message was received in the SP0:OOB_COMINIT state or the SP1:OOB_AwaitCOMX state since the last time the SP0:OOB_COMINIT state was entered". This variable is used in the SP1 state in the hot-plug timer timeout case to transition to SP0. 6.8.3.3.2 Transition SP1:OOB_AwaitCOMX to SP0:OOB_COMINIT This transition shall occur if the Hot-Plug Timeout timer expires. If the COMWAKE_Received state machine variable is set to zero and the ATTACHED SATA PORT SELECTOR bit is set to one in the SMP DISCOVER response (see 10.4.3.5) and the SMP DISCOVER LIST response (see 10.4.3.12.3), the state machine shall, before the transition: a) set the ATTACHED SATA PORT SELECTOR bit to zero in the SMP DISCOVER response and the SMP DISCOVER LIST response; and b) send a SATA Port Selector Change confirmation to the link layer. This particular sentence that you mentioned in the first paragraph of your email does not prohibit COMWAKE from being detected in some other states other than SP0 and SP1. In fact, besides the SP4: OOB_COMSAS state that you discovered that does receive "COMWAKE detected message", there is another state SP3: AwaitCOMINIT_Sent state that respond to COMWAKE detected message as well. The difference is SP3 and SP4 does not need to maintain the extra COMWAKE_Received state machine variable. I don't see any inconsistency here. Vicky ________________________________ From: owner-t10@t10.org [mailto:owner-t10@t10.org] On Behalf Of Chang, Neil Sent: Monday, July 31, 2006 6:43 PM To: t10@t10.org Subject: sas2r04 section 6.8 SP state machine SATA port selector support question 6.8 SP (phy layer) state machine 6.8.1 SP state machine overview ... If the phy supports SATA port selectors, the SP state machine shall maintain a COMWAKE_Received state machine variable to indicate whether a COMWAKE detected message was received in the SP0:OOB_COMINIT state or the SP1:OOB_AwaitCOMX state since the last time the SP0:OOB_COMINIT state was entered,... Later in 6.8.3.6 SP4:OOB_COMSAS state, it states (in page 210), Upon entry into this state, this state shall send a Transmit COMSAS message to the SP transmitter. This state waits for receipt of a COMSAS Transmitted message and/or a COMSAS Detected message. If the phy supports SATA port selectors, the ATTACHED SATA PORT SELECTOR bit is set to zero in the SMP DISCOVER response (see 10.4.3.5), and this state receives a COMWAKE Detected message, this state shall: a) set the ATTACHED SATA PORT SELECTOR bit to one in the SMP DISCOVER response; and b) send a SATA Port Selector Change confirmation to the link layer. Question: It states earlier that COMWAKE_Received state machine variable shall be maintained to indicate that COMWAKE_detected message was received in SP0 and SP1 states. But later in SP4:OOB_COMSAS state, it indicates that it could receive COMWAKE detected message. Is it just specification inconsistence? Or any comments are appreciated. Thanks, Neil Chang