Power Condition Mode Select interpretation of intent

Kevin D Butt kdbutt at us.ibm.com
Mon Aug 25 08:58:00 PDT 2008

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I have a question of the intent of the Power Condition mode parameters.
The following text is from SPC-4r16.
7.4.12 Power Condition mode page
The Power Condition mode page provides an application client with methods 
to control the power condition of a
logical unit (see 5.10). These methods include:
a) Specifying that the logical unit transition to a power condition 
without delay; and
b) Activating and setting of idle condition and standby condition timers 
to specify that the logical unit wait for a period of inactivity before 
transitioning to a specified power condition.
Item a) implies to me that there is a method of telling the target to "go 
to specified power condition immediately (i.e., now)".
Item b) implies to me that there is a method of specifying a timer value 
for when to transition to the power condition.
Is the intent of listing a) separately to infer that a timer value of zero 
is the "go immediately" command and that it is a one time event?  Or is 
the intent that the timer value is modified to be zero and the side effect 
of that modification is that the power condition is immediately 
transitioned to?  Stated differently, does a mode select specifying a 
power condition timer of zero modify that timer until the next mode select 
(or event that changes mode parameters) thereby causing a device to 
transition out of and back into that state on the receipt and completion 
of each command that causes a transition (e.g., write)?
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-2869 / 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com

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