Requirement for Overlapped Tag Checking in SPI-2

Jeffrey L Williams Jeffrey.L.Williams at
Fri Jan 30 11:25:52 PST 1998

* From the T10 (formerly SCSI) Reflector (t10 at, posted by:
* Jeffrey L Williams <Jeffrey.L.Williams at>

It was recently pointed out to me that SPI-2 kept the requirement for
overlapped tag checking even though SAM allows the protocol documents to
remove this requirement.

I am opposed to keeping this requirement for a number of reasons.  

As protocol chips become more and more automated, there are cases where
firmware is not even informed of a command arriving at the target. 
Keeping this requirement in SPI-2 implies that either the firmware has to
be informed of each command (a huge performance impact) or the chip has to
have a method to check for overlapped commands )adding cost and complexity
to the interface controller chip).

Keep in mind that this is an error that only occurs when an initiator
sends two tags of the same value for some reason.  This is an initiator
that is obviously broken.

FCP removes this requirement from the protocol.

I would like to see this requirement removed from SPI-2.  What are the
options for bringing this into the current editing?  Does this have to be
a public review comment?


Jeffrey L. Williams
Western Digital Rochester                 
Enterprise Storage Group
Office: (507) 286-7589
Fax: (507) 286-7528
Pager: (888) 858-PAGE   ID: 120826
e-mail: Jeffrey.L.Williams at

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