Quantum ATL PowerStor L200 Series, User Manual

Page: 69 / 106

Chapter 4 SCSI Interface
General SCSI Bus Operation
ATL PowerStor L200 Series Library User’s Guide 53
Unit Attention
Condition
4
Queued Unit Attentions are implemented on this device, and are
maintained separately for each Initiator. Unit Attentions are created in
the following circumstances:
•
power on
•
Bus Reset
•
Bus Device Reset message
• when the media may have changed asynchronously
•
another initiator changed the Mode Parameters
It is not unusual for a firmware (microcode) update to complete two
queued Unit Attentions. Due to a limited number of Unit Attention
buffers, if an initiator does not clear Unit Attentions queued for it, at
some point the library stops generating new Unit Attentions for that
Initiator-LUN (I-L) combination (but existing ones are left queued).
Behavior Around
Power-On and SCSI
Bus Reset
4
All device SCSI lines go to high impedance when the library is
powered off.
The library does not generate any spurious signals on the SCSI bus at
power-on.
Within 5 seconds of power on, and within 250 milliseconds (typically
under 4 ms) after a Bus Reset, the library responds to SCSI bus
selections and returns appropriate, normal, responses. Tape motion
commands are returned with
CHECK CONDITION
status,
Sense Key
Not Ready
, until the media has been made ready.
The Hard Bus Reset option is implemented.
The library recognizes multiple bus resets in succession and bus resets
of arbitrarily long duration. It recovers within the time limits specified
above, following the last bus reset.
Other SCSI
Functionality
4
Linked commands and untagged queuing are supported.
Bus Phases
4
The library conforms to the bus state transition table shown in the
SCSI-2 standard, “Phase Sequences." The information in the following
sections also applies.
Attention Signal
Response
4
The library responds to an ATN condition at every phase transition, as
long as the initiator sets the ATN bit before the target deasserts the
REQ for the last byte of the previous phase. Generally ATN is
recognized immediately by the library, and it changes the bus phase to
Message Out.