Unit Attention - Sun Microsystems storagetek sl500 Reference Manual

Bus Conditions

Unit Attention

The Unit Attention Condition is a specific form of the Contingent Allegiance
Condition. The target generates a Unit Attention condition for each initiator for:
A hard reset condition
■
A power-on reset
■
A SCSI Bus Device Reset message
■
Example: A library is installed on the SCSI bus, but the library is powered off. When
powering-on, the library generates a Unit Attention condition to all initiators
attached to the SCSI bus. The initiator must clear the Unit Attention condition
before communication with the library can occur.
A target also generates a Unit Attention condition for:
Changing the removable medium
■
Changing the Mode Select parameters
■
Preempting Persistent Reservations
■
The Unit Attention condition persists for each initiator until that initiator issues a
command to the target or logical unit (other than Request Sense or Inquiry
commands) for which the device returns a Check Condition status.
If the next command from that initiator to the logical unit (following the Check
■
Condition status) is Request Sense, the Unit Attention sense key is returned. If
the target receives any command other than Request Sense, the Unit Attention
condition is lost.
If the target receives an Inquiry command from an initiator with a pending Unit
■
Attention condition (before the device reports Check Condition status), the
device completes an Inquiry command and does not clear the condition.
If the target receives a Request Sense command from an initiator with a pending
■
Unit Attention condition (before the device reports Check Condition status), the
device reports any pending sense data and preserves the unit attention
condition.
If an initiator issues a command other than Inquiry or Request Sense while a
■
Unit Attention condition exists for that initiator, the device returns Check
condition status with the Unit Attention sense key and clears the Unit Attention
condition.
22 SL500: Interface Reference Manual • July 2008 Revision: F • 96122