February 18, 1991 X3T9.2/91-008 R01 To : John Lohmeyer, Chairman, X3T9.2 From : Gary R. Stephens IBM Corporation D67E/060-1 9000 S. Rita Rd. Tucson, Az 85719 (602) 799-2246 Subject: SCSI-2 Message System Cleanup In independent studies of sections of the SCSI-2 document, two anomalies have been found which need attention before SCSI-2 becomes a standard. I found one error in Section 5.2.1 concerning RESELECTION and Jeff Stai found one in Section 5.6.7. The two are loosely related and proposed corrections follow. Gary R. Stephens Section 5.2.1. Attention Condition The response to the ATN signal being true during the RESELECTION phase (item 6, page 5-13, Revision 10c) can cause the target to create a reconnection for a nonexistent nexus as it is currently worded. If a reconnection for a LUN is made in tagged queueing mode, strict adherence to the rule in item 6 causes an invalid nexus to be formed of type I_T_L rather than I_T_L_Q since the target is required to enter the MESSAGE OUT phase after the IDENTIFY message rather than after identification is complete, which in this example requires transmission of the SIMPLE QUEUE TAG message to complete the nexus identification. If the initiator raises ATN during the RESELECTION phase, it really does not care what LUN is reconnecting, only that the target is reconnecting. Per- forming partial identification is really worse than performing no identifica- tion at all. In addition, the current wording of item 6 is contrary to Section 5.2.1, par- agraph 3, sentence 1. The proposed solution is consistent with this general rule that the next phase following the assertion of ATN during one phase shall be the MESSAGE OUT phase. The proposed solution is as follows: Replace item 6 of section 5.2.1 with the following text: (6) If the ATN signal becomes true during a RESELECTION phase, the target shall enter the MESSAGE OUT phase following successful completion of the RESELECTION phase. END OF REPLACEMENT TEXT Section 5.6.7. IDENTIFY The last paragraph of Section 5.6.7 requires restoring pointers without mention of the possibility of the presence of the SIMPLE QUEUE TAG message as in the example above. The following is proposed replacement text for the last paragraph of section 5.6.7, page 5-23, Revision 10c: An implied RESTORE POINTERS message shall be performed by the initiator fol- lowing successful identification of the nexus during the MESSAGE IN phase of a reconnection and before the negation of the ACK signal for the next transfer following the successful identification. Identification is considered successful during an initial connection or an initiator reconnect when the target detects no error during the transfer of the IDENTIFY message and an optional queue tag message in the MESSAGE OUT phase immediately following the SELECTION phase. See Section 5.5 for the ordering of the IDENTIFY and queue tag messages. See Section 5.1.9.2 for handling target detected errors during the MESSAGE OUT phase. Identification is considered successful during a target reconnect when the ATN signal is not asserted during the transfer of either the IDENTIFY message or the SIMPLE QUEUE TAG message for an I_T_L_Q nexus in the MESSAGE IN phase immediately following the RESELECTION phase. See Section 5.5 for the ordering of the IDENTIFY and queue tag messages. See Section 5.2.1, item 4, for handling target detected errors during the MESSAGE IN phase. END OF REPLACEMENT TEXT