Dynamic Idle?

Dynamic Idle?

[Peter Reid]

[-- Attachment #1.1: Type: text/plain, Size: 310 bytes --]

What do the following terms mean in terms of linux power management for
embedded systems.

 1) Dynamic - Idle
 2) Suspend-Resume

Do they mean the same thing? or are they different, If so how?

Could you please explain with a scenario of how these states occur in
real world embedded systems.


Regards,
Reid.

[-- Attachment #1.2: Type: text/html, Size: 363 bytes --]

[-- Attachment #2: Type: text/plain, Size: 0 bytes --]

Re: Dynamic Idle?

[Alan Stern]

On Fri, 7 Nov 2008, Peter Reid wrote:

> What do the following terms mean in terms of linux power management for
> embedded systems.
> 
>  1) Dynamic - Idle
>  2) Suspend-Resume

Dynamic and Idle are two separate terms.  Dynamic means that something 
is running.  Idle means that something either isn't running or else is 
running but isn't doing anything.

Suspend means to put either a single device or else the entire system
into a non-operational low-power state.  Resume means to put the device
or the system back into an operational full-power state.

> Could you please explain with a scenario of how these states occur in
> real world embedded systems.

Suppose an embedded system has a USB device attached.  At times when 
the device isn't being used, the system could put it into a low-power 
state to conserve energy.  When the system needs to use the device, it 
would first have to resume the device.

Alan Stern

Re: Dynamic Idle?

[Peter Reid]

[-- Attachment #1.1: Type: text/plain, Size: 1345 bytes --]

Hi Alan,


On Fri, Nov 7, 2008 at 8:36 PM, Alan Stern <stern@rowland.harvard.edu>wrote:

> On Fri, 7 Nov 2008, Peter Reid wrote:
>
> > What do the following terms mean in terms of linux power management for
> > embedded systems.
> >
> >  1) Dynamic - Idle
> >  2) Suspend-Resume
>
> Dynamic and Idle are two separate terms.  Dynamic means that something
> is running.  Idle means that something either isn't running or else is
> running but isn't doing anything.
>
> Suspend means to put either a single device or else the entire system
> into a non-operational low-power state.  Resume means to put the device
> or the system back into an operational full-power state.


  Do you mean to say that:

   Dynamic = Active
   Idle = Idle
   Suspend = Low Power State
   Resume = Active/Dynamic

  If so, what is the difference between suspend and Idle?

  Are both the same and what are OFF State/Retention State as well?


Thank you.

Regards,
Reid.








>
>
> > Could you please explain with a scenario of how these states occur in
> > real world embedded systems.
>
> Suppose an embedded system has a USB device attached.  At times when
> the device isn't being used, the system could put it into a low-power
> state to conserve energy.  When the system needs to use the device, it
> would first have to resume the device.
>
> Alan Stern
>
>

[-- Attachment #1.2: Type: text/html, Size: 2104 bytes --]

[-- Attachment #2: Type: text/plain, Size: 0 bytes --]

Re: Dynamic Idle?

[Alan Stern]

On Fri, 7 Nov 2008, Peter Reid wrote:

>   Do you mean to say that:
> 
>    Dynamic = Active
>    Idle = Idle
>    Suspend = Low Power State
>    Resume = Active/Dynamic

More like: Resume = High Power State.  Or better still:

	Suspend = Go to low-power state
	Resume = Return to high-power state

>   If so, what is the difference between suspend and Idle?

A suspended device must, of course, be idle.  But an idle device need
not be suspended.  A device can remain in a high-power state even while
it's not doing anything.

>   Are both the same and what are OFF State/Retention State as well?

Presumably "OFF state" means no power at all.  I don't know what 
"Retention State" means.

Alan Stern

Re: Dynamic Idle?

[Amit Kucheria]

On Fri, Nov 07, 2008 at 10:54:58AM -0500, Alan Stern wrote:
> On Fri, 7 Nov 2008, Peter Reid wrote:
>
> >   Are both the same and what are OFF State/Retention State as well?
> 
> Presumably "OFF state" means no power at all.  I don't know what 
> "Retention State" means.

"Retention state" is used in some embedded architectures to mean a low-power state of the processor where context is maintained. e.g. Putting RAM in self refresh mode, so that devices do not have to initialise themselves when coming out of the low-power state.

/Amit

-- 
-------------------------------------------------------------------------
Amit Kucheria			amit.kucheria@verdurent.com
Kernel Developer, Verdurent
--------------------------------------------------------------------------