Power Management Questions

Gerry_Houlder at notes.seagate.com Gerry_Houlder at notes.seagate.com
Tue Nov 10 08:13:13 PST 1998


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Gerry_Houlder at notes.seagate.com
*
I have added my answers after Keiji Kaneoka's questions:

QUESTION 1
In Sleep state, it defines that "no commands, except for reset can
be received." Can I take this to mean the device shall not response to
SELECTION, which means there is no way to receive the message from
initiators?

ANSWER 1:
   Yes. when device is in sleep state, the device doesn't accept
selection so there is no way to receive messages. I belive the MMC-2
wording is wrong. The device reset wording should be replaced with
WAKEUP task management function as described in SBC and SPI-3.
   I am also confused why MMC-2 defines device reset as ABORT TASK
SET or CLEAR TASK SET functions. Most SCSI designers would think device
reset means LOGICAL UNIT RESET or TARGET RESET management functions.
This wording needs further examination by the T10 committee.

QUESTION 2
If a device in Sleep mode is allowed to response to SELECTION, but
initiators may not send the messages. How should the device act, when
it detects a message other than TARGET RESET or ABORT/CLEAR TASK SET??
Should the device go to BUS FREE Phase immediately after it detects the
condition??

ANSWER 2:
   Since device isn't allowed to accept selection, question is moot.

QUESTION 3
If the device shall wakeup by TARGET RESET or ABORT/CLEAR TASK SET
message, how does the device detect the ABORT/CLEAR TASK SET if "no
commands, except for reset can be received." ??

ANSWER 3:
   Only hard SCSI RESET signal can cause wakeup.

QUESTION 4
What is the real way to make the device wakeup from Sleep state?
How can I recognize some of them when in Sleep state? To receive them I
must
be selected but in Sleep state I do not respond to Select....

 a) RST Signal,
 b) TARGET RESET Message,
 c) ABORT/CLEAR TASK SET message
 d) All of the above

b) and c) need the response to the SELECTION.

ANSWER 4:
   Only a) can cause wakeup.

QUESTION 5
In the description of Sleep State, it is defined that
 "disc(s)/cassette may be manually ejected or inserted while in sleep
  state, independent of any lock/unlock mechanism employed. For the Host
  to consistently rely on the Logical Unit Media Status Notifications,
  when the Logical Unit is unable to determine if media has been changed
  while the Logical Unit was in the sleep state, the Logical Unit shall
  report a New Media Event on the next GET EVENT/STATUS NOTIFICATION
  (Media Status) Command."

Should a device in the Sleep state detect the user EJECT/LOAD by eject
button on the front panel?

ANSWER 5:
   I don't have experience in designing or using removable media devices
so my answer is only opinion. I believe a user would want the drive to
respond to the LOAD/EJECT button even if the drive is in sleep state.
Thus when the user pushes LOAD/EJECT button, the drive should wake up
so that media can be loaded/unloaded as requested. It would be OK if this
operation takes a little longer when the drive must wake up first.


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