Power Management Questions

Keiji Kaneoka kaneoka at dm.mat.mke.mei.co.jp
Mon Nov 9 17:16:29 PST 1998


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Keiji Kaneoka <kaneoka at dm.mat.mke.mei.co.jp>
*
Hello,

I have questions regarding the Power Management Function of SCSI-3. 
My job is Firmware Engineer for CD/DVD Devices, and the following 
questions are related to this area. 

My problem is trying to build a standards-compliant device, but the 
standards say different things about how to operate. It seems to be 
impossible to implement correctly from the documents.

Can anyone help me to understand the device operation in  Sleep 
State, please??

 - SCSI-3 has the Power Management Function from SCSI-2.
   It will be established by using Power Condition field of START/STOP
   UNIT Command(1Bh). There are four defined power states: Active, Idle, 
   Standby and Sleep.

 - In SBC, it is defined that "If the START STOP UNIT command is issued 
   with the POWER CONDITION field set to 5h the server shall:
   a) suspend any Power Condition timers that are active on receipt 
      of the START STOP UNIT command until a WAKEUP task management 
      function is received by the device server;
   b) not respond to a task requests until a WAKEUP task management 
      function is received by the device server."

 - In SPI-3, it is defined that
   "12.10.4.1.8 WAKEUP
   The SCSI parallel interface services request the initiator issue 
   a hard reset (see 11.2.2) to the selected SCSI device."

>From these definitions, I can guess the device will wakeup from Sleep 
state when it detects that the RST Signal is asserted but then there are 
other places which make this unclear. 

 - In SCSI-3 MMC-2, it is defined that
  
  "A Device Reset received while in Sleep state returns the power state
   to Standby." 

and 

  "Device Reset: ABORT TASK SET task management function
               : CLEAR TASK SET task management function"

I found the ABORT TASK SET message and CLEAR TASK SET message in SPI3, and 
these require selection in order to be executed. 


 - In Mt Fuji3, it is defined that 

  "C-4.4 Power management and Device Reset in SCSI
   When a SCSI Device is in the Power Managed Sleep state, the SCSI 
   Target Reset shall be used to wake the device."

I am confused by the above definitions, and here are some questions. I hope 
the answers to these questions will help solve my confusion. 

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? 

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??

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." ??

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 resonse to the SELECTION.

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?

Best Regards,
Keiji Kaneoka

Matsushita-Kotobuki Electronics Ind., Ltd.
+81-89-966-3311
e-mail:kaneoka at dm.mat.mke.mei.co.jp


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