Contigent Allegiance question

sgaskill at sgaskill at
Tue Aug 15 11:12:04 PDT 1995

Hello there, I have a couple of questions.

1. Which of the SCSI-3 documents describes the Contingent Allegiance condition? 
I snooped through SIP, SPI, SPC -- but couldn't find it.  SBC maybe?

2. Is a SCSI-2 target that supports tagged command queuing and CA (but not ECA) 
permitted to enqueue commands from other initiators?  Or _must_ it respond with 
BUSY status until the CA condition is cleared?

The SCSI-2 spec (about a dozen paragraphs into section 7.8.2, Tagged Queuing) 
states "The target returns BUSY status to other initiators while the contingent 
allegiance or extended contingent allegiance condition exists."  Two pages back,
in section 7.7, I find "While the extended contingent allegiance condition 
exists, the target shall respond to any other request for accessto the logical 
unit from another initiator with BUSY status."

Does the lack of the word "shall" in the first quote mean that the target does 
not have to respond with BUSY status, and can accept more commands (presumably 
to be placed into the frozen queue)?  Maybe I'm trying too hard to read between 
the lines and it's safer to think that because it doesn't say "may return BUSY 
status" that it MUST return BUSY status?

I have a SCSI book that states the target may accept (enqueue) commands from 
other initiators, but it's not so clear to me from the actual spec.

Thanks for your help,


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