Wide or Narrow?

SSchmitz at attotech.com SSchmitz at attotech.com
Thu Aug 26 13:46:26 PDT 2004


* From the T10 Reflector (t10 at t10.org), posted by:
* SSchmitz at attotech.com
*

George,

I should have mentioned that this is negotiation initiated by the
initiator.  Anyway, in my opinion, WDTR can never be a requirement prior to
SDTR either way since some devices do not support it.  Your quote from
section 4.12.6 seems very ambiguous and almost incorrect.

Also remember that I am talking about three separate commands.  Sync DT
(Wide) communication was established successfully on the second command so
I believe SDTR-only negotiation should be legal on the third command and
the bus should be wide.

-Scott




|---------+---------------------------->
|         |           George Penokie   |
|         |           <gop at us.ibm.com> |
|         |                            |
|         |           08/26/2004 03:43 |
|         |           PM               |
|         |                            |
|---------+---------------------------->
  >------------------------------------------------------------------------------------------------------------------------------|
  |                                                                                                                              |
  |       To:       SSchmitz at attotech.com                                                                                        |
  |       cc:       owner-t10 at t10.org, t10 at t10.org                                                                               |
  |       Subject:  Re: Wide or Narrow?                                                                                          |
  >------------------------------------------------------------------------------------------------------------------------------|





Scott,

The sequence you list (i.e., WDTR - PPR - SDTR) is not a legal sequence.
The correct sequence should be (i.e., WDTR - PPR - WDTR - SDTR). These
rules are stated in SPI-5 as:

4.12.6 Message restrictions
....
WDTR and SDTR may be originated by either SCSI target ports or SCSI
initiator ports. Since WDTR resets all the values that SDTR sets (see
4.12.4.1), it shall be sent first if both are needed.

SCSI target ports capable of wide transfer agreements shall originate
negotiation with WDTR followed with SDTR.

However, that said, Table 2 in section 4.12.4.1 (Negotiable fields
introduction) states that the TRANSFER WIDTH EXPONENT is to remain
unchanged during an SDTR requires the bus to remain in the state set in the
PPR message which in your example is wide.

Bye for now,
George Penokie

Dept 2C6  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208   FAX: 507-253-2880



                                                                           
 SSchmitz at attotech.com                                                     
 Sent by: owner-t10 at t10.org                                                
                                                                           
                                                                        To 
 08/26/2004 11:49 AM                                           t10 at t10.org 
                                                                        cc 
                                                                           
                                                                   Subject 
                                                               Wide or     
                                                               Narrow?     
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           





* From the T10 Reflector (t10 at t10.org), posted by:
* SSchmitz at attotech.com
*

Consider three SCSI commands preceeded by the following negotiation:

1.  Async Narrow using the WDTR message (message bytes: 01 02 03 00).
2.  Sync DT 160 using the PPR message (message bytes: 01 06 04 09 00 3E 01
02).
3.  Sync ST 80 using the SDTR message (message bytes: 01 03 01 0A 1F).

At this point, is the bus wide or narrow?  In other words, should separate
states be maintained for PPR vs. WDTR/SDTR negotiation implying that the
bus is narrow or should one state be maintained implying that the bus is
wide?

-Scott Schmitz


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