ACA handling for temp initiators - response

Charles Monia, SHR3-2/W3, 237-6757 14-Jun-1994 1528 monia at
Tue Jun 14 12:26:35 PDT 1994

John Schieble wrote:
2) The preferred method (A) does not allow for multiple ACA conditions
   to be outstanding at once.  This is especially important to Async
   Event Reporting cases, where the error condition is reported to a
   group of initiators.  Each initiator has its own ACA condition that
   if only reset for itself when it issues a Clear ACA Condition
   message.  Other initiators could have their ACA conditions still

>1. For a given task set, there is no such thing as multiple ACA conditions
>   outstanding. There is never more than one ACA condition active. When that
>   ACA is cleared, there won't be another until a subsequent command
>   completes with CHECK CONDITION or COMMAND TERMINATED status.

SAM QUESTION: If the condition states in 2) where AER is issued to a set
              of initiators.  If an initiator frees his ACA and his
              command is next on the queue, can his command execute,
              even if other initiators have ACA conditions?
> First, an AER does not result in an ACA condition. an ACA  condition
> only goes into effect  when a command terminates as described above.
> Therefore, If AER's were issued as you state, there would be
> no ACA conditions to be handled.
> I suspect what you're referring to is the case where there are several
> errors to be reported, such as pending unit attention conditions.for
> multiple initiators. In the case of a unit attention condition, the logical
> unit has a choice of reporting mechanisms. It can report a given occurrance
> with an AER or by terminating a command with CHECK CONDITION status, but
> not both. If it chooses AER, then there would be no auto contingent 
> allegiance condition as a result of the unit attention.
> If the logical unit chooses to report the condition by returning
> a CHECK CONDITION  status, then it may do so as soon as
> the command is eligible to complete, as defined by the queueing model.
> At that point, a new ACA would be in effect, which must be cleared
> by the appropriate initiator. Eventually, each pending condition would
> be reported and cleared in this manner.
Charles Monia
Digital Equipment Corporation
334 South Street
Shrewsbury, MA 01545

Tel: (508)841-6757		Email: monia at
Fax: (508)841-6100

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