Save Data Pointer questions

Jeff Williams JWILLIAM at wdroc.wdc.com
Fri Mar 7 09:52:00 PST 1997


* From the SCSI Reflector (scsi at symbios.com), posted by:
* Jeff Williams <JWILLIAM at wdroc.wdc.com>
*

> Generally you don't see the SAVE DATA POINTER after
> the COMMAND phase, but it seems I have seen this before.  Because there   
is
> an implied RESTORE pointer message on a reconnect, the COMMAND and   
STATUS
> (and DATA) pointers are restored to the last saved values, so there is   
not
> need to do the SAVE DATA pointer message after the COMMAND phase, but   
SCSI
> standard does say SHALL send 0204 sequence after all successful   
connections.

I agree with all of this except the point that SCSI says
you shall send the 0204.  It specifically says ".. shall end
each successful connection (except possibly the last) with
a SDP-DC message sequence".  This specifically allows the
last connection to NOT have the SDP.  I have seen different
customers require or disallow the SDP before a DC on the last
set of data on a write.  Some don't want the SDP since it
takes a usec to do, some want it for consistency.

It should also be noted that the saved values for command and
status are always pointing to the start of the command or status.

Regards,
Jeff

 -------------------------------------------------------------
Jeffrey L. Williams                    Office: (507) 286-7589
Western Digital Rochester                 Fax: (507) 286-7528
Enterprise Storage Group       e-mail: jwilliam at wdroc.wdc.com
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