X3T9.2/91-211
                   SCSI-2 CAM Change Proposal

Title:    Discussion of SIM handling of CAM Command Timeouts
Author:   Al Youngwerth, Extended Systems
Date:     January 8, 1992

References

1.    X3T9.2-90-186, SCSI-2 Common Access Method - Transport
      and SCSI Interface Module, rev 2.4, I. Dal Allan (Ed.)

Discussion

CAM rev 2.4, does not specify how the SIM handles a CCB SCSI IO
command that has timed-out.  For example, when a command times-out,
the SIM implementor can choose whether or not to attempt an abort
of the command before it returns the CCB with a status of Command
Timeout.  The Peripheral Driver needs to know how the SIM handles
a command timeout in order to take proper action.

Change Proposal

Insert the following section as 6.6, resequence the current
sections 6.6 through 6.8 as 6.7 through 6.9.

6.6 SIM Handling CCB SCSI IO Command Timeouts

In the event of a CCB SCSI IO Command Timeout, the SIM shall:

a) Place its internal queue for the LUN into the frozen state.
b) Without freeing its internal resources for the command, the
SIM will notify the Peripheral Driver of the time-out by
setting the CCB's CAM status to Command Timeout and performing
the callback (if enabled).  

At this point, the timed-out CCB is still active within the SIM
and its resources must not be freed until the Peripheral Driver
is able to recognize that the timed-out CCB's CAM status has
changed from Command Timeout to some other status.  The
Peripheral Driver must be able to recognize a change in the
timed-out CCB's CAM status and if enabled, another callback for
it.  

It is the Peripheral Driver's responsibility to take corrective
action for the timed-out CCB.  It is recommended that the
Peripheral Driver attempt to abort the command.  If the abort
command does not create a change in the timed-out CCB's CAM
status in a reasonable amount of time, a Bus Device Reset or
SCSI Bus Reset command may need to be issued to force the
timed-out CCB's CAM status to change.