Open SCSI Integrator's Manual for NonStop S-Series Servers

The SCSI SAC
Open SCSI Integrator’s Manual for NonStop Servers—422988-002
7-11
Reconnection
cycle. The SCSI SAC is set to the default agreement following a SCSI RST condition or
a SCSI SAC power on/off cycle.
Reconnection
A target LUN with disconnection privilege is allowed to disconnect from the Open SCSI
target-to-SCSI SAC interface after the completion of a Disconnect message sequence.
The interrupted SCSI operation can be resumed by the target through the reselection
sequence. The reconnecting LUN is identified through an Identify message during the
message-in phase.
If the reconnection is valid, the SCSI SAC performs an implicit Restore Pointers
operation. That is, the operation is performed but the corresponding message is not sent.
Invalid or illegal reconnection is terminated by the SCSI SAC with an Abort message.
The SCSI SAC does not notify the host of an illegal reconnection.
Autosense
Devices on the bus and their corresponding application programs must support
autosense. See the discussion of contingent allegiance conditions in the SCSI-2
specification.
The SCSI SAC performs an autosense operation when the main SCSI operation
terminates with a Check Condition SCSI-status byte but returns no other status.
Autosense then uses the SCSI Request Sense command to obtain the sense buffer from
the target LUN. The allocation length in the request-sense command descriptor block
(CDB) is no less than 18 bytes and no more than the autosense length.
If sense data is received from the target, the SCSI SAC formats an autosense parameter
with the sense data and returns it to the host in the response packet.
Errors during autosense are reported in the CAM-status field as autosense failure.
The SCSI status field in the response packet reports the Check Condition status resulting
from the main SCSI operation.
Target-Initiated Retry
The SCSI SAC supports the retry of command, data, and status phases by the target. The
retry can be requested explicitly by the target through the Restore Pointers message or
implicitly by disconnecting and reconnecting in order to retry.
The SCSI SAC expects disconnection from the target after one of the following events:
•
A SCSI RST signal
•
An Abort message sent to the target
•
A Bus Device Reset message sent to the target
•
A valid Disconnect message received from the target