X3T9.2/91-150 September 9, 1991 To: X3T9.2 Committee From: John Lohmeyer, NCR Principal Member of X3T9.2 Subject: SDTR and WDTR Clarification In George Hahn's 91-118 document, he identifies an area of SCSI-2 that is not absolutely clear. The issue also applies to the wide data transfer agreement. I have drafted the following wording to clarify the concept in the SCSI-3 SIP document. If we have to create another revision of SCSI-2, I would recommend that this clarification also be included in SCSI-2 (but not if it were to delay the document). Recommended additions are shown with a change bar in column 1. There are no deletions and the tables did not change. 5.6.21 SYNCHRONOUS DATA TRANSFER REQUEST Message Table 5-9: SYNCHRONOUS DATA TRANSFER REQUEST +=====-========-========-========-========-========-========-========-========+ | Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |Byte | | | | | | | | | |=====+=======================================================================| | 0 | Extended message (01h) | |-----+-----------------------------------------------------------------------| | 1 | Extended message length (03h) | |-----+-----------------------------------------------------------------------| | 2 | SYNCHRONOUS DATA TRANSFER REQUEST code (01h)| |-----+-----------------------------------------------------------------------| | 3 | Transfer Period Factor | |-----+-----------------------------------------------------------------------| | 4 | REQ/ACK Offset | +=============================================================================+ |SYNCHRONOUS DATA TRANSFER REQUEST (SDTR) messages (Table 5-9) are used to |negotiate a synchronous data transfer agreement between two SCSI devices. The |agreement applies to all logical units and target routines of both SCSI |devices, regardless of the target or initiator role. That is, if SCSI device |A, acting as an initiator negotiates a synchronous data transfer agreement with |SCSI device B (in the target role), then the same data transfer agreement |applies to SCSI devices A and B even if SCSI device B changes to the initiator |role. |A synchronous data transfer agreement only applies to the two SCSI devices that |negotiate the agreement. Separate synchronous data transfer agreements are |negotiated for each pair of SCSI devices. |An SDTR message exchange shall be initiated by an SCSI device whenever a previously-arranged data transfer agreement may have become invalid. The agreement becomes invalid after any condition which may leave the data transfer agreement in an indeterminate state such as: a) after a hard reset condition; b) after a BUS DEVICE RESET message and; c) after a power cycle. . . . 5.6.23 WIDE DATA TRANSFER REQUEST Message Table 5-10: WIDE DATA TRANSFER MESSAGE +=====-========-========-========-========-========-========-========-========+ | Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |Byte | | | | | | | | | |=====+=======================================================================| | 0 | Extended message (01h) | |-----+-----------------------------------------------------------------------| | 1 | Extended message length (02h) | |-----+-----------------------------------------------------------------------| | 2 | WIDE DATA TRANSFER REQUEST code (03h) | |-----+-----------------------------------------------------------------------| | 3 | Transfer Width Exponent | +=============================================================================+ |WIDE DATA TRANSFER REQUEST (WDTR) messages (Table 5-10) are used to negotiate a |transfer width agreement between two SCSI devices. The agreement applies to |all logical units and target routines of both SCSI devices, regardless of the |target or initiator role. That is, if SCSI device A, acting as an initiator |negotiates a transfer width agreement with SCSI device B (in the target role), |then the same transfer width agreement applies to SCSI devices A and B even if |SCSI device B changes to the initiator role. |A transfer width agreement only applies to the two SCSI devices that negotiate |the agreement. Separate transfer width agreements are negotiated for each pair |of SCSI devices. |A WDTR message exchange shall be initiated by an SCSI device whenever a previously-arranged transfer width agreement may have become invalid. The agreement becomes invalid after any condition which may leave the data transfer agreement in an indeterminate state such as: 1) after a hard reset condition; 2) after a BUS DEVICE RESET message and; 3) after a power cycle. . . .