Selection with ATN in IU mode question

Elliott, Robert (Hou) Robert.Elliott at
Tue Sep 19 12:44:51 PDT 2000

* From the T10 Reflector (t10 at, posted by:
* "Elliott, Robert (Hou)" <Robert.Elliott at>
> * From the T10 Reflector (t10 at, posted by:
> * Ken Erickson <Ken.Erickson at>
> *
> What is the expected behavior of a target that has just 
> sent a Message Reject message followed by a WDTR w/ 
> narrow mode to an initiator while in the IU mode?  To me 
> it appears that since the target is no longer in IU mode
> that the target should go to a BUS FREE phase as it did 
> when it entered the IU mode.

This is from SPI-3 section, selection with attention
with information units enabled. 

I think it is trying to cover what happens when an  Ultra 3+ 
IU-capable initiator is hot-swapped with an non-IU capable 
initiator.  That initiator will try sending an IDENTIFY
link control message.  It is not obligated to follow that with 
WDTR/SDTR; it may assume async mode.  As soon as the target 
detects this initiator discrepancy, the target needs to clear 
all existing tasks and switch to non-IU mode.  The WDTR/SDTR 
negotiation does this.  It needs to go BUS FREE for a few
1) it rejected the IDENTIFY so has no LUN or tag information.
The initiator might assert ATN and resend, but I doubt it.
2) BUS FREE is customary whenever IU mode changes (or any PPR 
is done) 
3) BUS FREE is customary whenever an abort task set occurs.

> Also, why was it chosen that if the initiator sent a message 
> while selecting a target with ATN and the message is not a
> PPR message or a TASK MANAGEMENT message that the target will 
> respond by sending a WDTR.  Why not send a PPR message?  That 
> is how the initiator started the IU process.

Targets are prohibited from initiating PPR because they don't
control domain validation.  Imagine an Ultra 3 initiator
and Ultra 3 target connected via an Ultra 2 expander.  PPR
negotiation will successfully enable DT despite the fact that
the expander is there, incapable of DT mode.  Ultra 3 runs 
the P_CRCA signal in the opposite direction of Ultra 2
during writes.  After PPR, the subsequent data phase needs 
to be a read, or bus contention will result on P_CRCA.  If the
command is from an initiator running domain validation, it
will always be a read and work fine.  If the command is any
arbitrary command (which it could be if the target is choosing
when to request PPR), it certainly could be a write and 
cause trouble.

> Thanks,
> Ken Erickson
> Quantum Corp.

PC: Robert.Elliott at
UNIX: relliott at

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