ACA bit = 0 mandatory?

Gerry Houlder Gerry_Houlder at
Tue Sep 20 14:50:07 PDT 1994

>From the 9/14 working group, it seemed like we made it mandatory to support the
ACA bit = 0 value in the control byte of the CDB. The discussion talked about
the "autoclear" feature in most serial protocols clearing the allegiance
quickly because it occurred right after the CHECK status. The discussion didn't
talk about the response for deferred errors, however.
A deferred error should should cause the device to stop executing any commands
|from the command queue until the "autosense" function occurs. This means the
target must find a new command from the same initiator that still hasn't
reported status (a pending command could satisfy this, if there is one) and
terminate it with CHECK status and perform autosense. During this period, the
device must report ACA ACTIVE or BUSY status to commands from other initiators.
This could be a much longer interval than portrayed at the meeting. If we now
have a "SCSI-3" version of ACA=0 as well as a "SCSI-2" version of ACA=0, I hope
a description of deferred error handling will occur in the "SCSI-3" description
of it, at least.
Gerry Houlder -- Gerry_Houlder at
Seagate Technology   -   920 Disc Drive   -   Scotts Valley, CA 95066 USA
Main Phone 408-438-6550   -   Email Problems postmaster at
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### Subject:     ACA bit = 0 mandatory?
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