QAS question

Richard Moore richard.moore at
Tue Feb 27 11:58:18 PST 2001

* From the T10 Reflector (t10 at, posted by:
* Richard Moore <richard.moore at>
Bruce wrote:

>My understanding is that the initiator is required to assert ATN on the QAS
>message if he detects a parity error, before deasserting ACK.  All QAS
>devices must sample ATN on the ACK deassertion of a QAS message, and ignore
>the message if ATN is asserted.

That's correct. The second list in 10.5.4, procedure for a QAS-enabled
device to obtain the bus, says "When the SCSI device detects the ACK
signal being false for the QAS REQUEST message and the attention condition
is cleared..." I think this wording is a bit confusing. It almost seems to
be saying that "if there is an attention condtion, wait for it to clear..."
I think it would be clearer if it said, "...and the initiator did not raise
an attention condition for the message...".

>I assume that the target that sent the QAS message would go to MSG_OUT
>just like with any ATN assertion?  And the initiator would send ???

Yes. Although the first list in 10.5.4 doesn't say what the disconnecting
should do if it sees an attention condition (it says "if the initiator did
not create an attention condition..."), I think the normal requirements
for a target when an attention condition is raised apply here. The initiator
should send MESSAGE PARITY ERROR, should it not?

 -- Richard Moore
    QLogic Corp.
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at

More information about the T10 mailing list