power saving

power saving

[Tania Oka]

I would like to reduce power consumption on a custom MPC855T board.  I
notice in arch/ppc/kernel/idle.c idled() that the power saving code
seems to be skipped for processors other than 603/750 types.  Can anyone
tell me why that is?  Is it not a good idea on the 855 for some reason?
Is there anyone who has tried this on the 855 (or 850 or 860)?  Any
comments on the general subject welcome.

Thanks


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Re: power saving

[Dan Malek]

Tania Oka wrote:
>
> I would like to reduce power consumption on a custom MPC855T board.

This has been asked before, and you can read about it in mailing
list archives.

Basically, the MPC8xx processors have a dynamic power management
system that doesn't gain much from just doing something in the idle()
loop.  The majority of the power is consumed by peripherals.  If they
are not enabled, they automatically power down.  All of the MPC8xx
drivers "do the right thing" on open and close to power up/down
peripherals.

If you have some very low power standby requirement, you need to add
lots of power management software to do things like power down/up
any external peripherals on your board, put DRAM in autorefresh
mode, shut down the clocks and put the processor into a deep sleep.
You could look at some of the PowerMac power management code for
design ideas.


	-- Dan

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Re: power saving

[August Hoerandl]

On Monday 07 May 2001 09:49 pm, Dan Malek wrote:
> Tania Oka wrote:
> > I would like to reduce power consumption on a custom MPC855T board.
>
> This has been asked before, and you can read about it in mailing
> list archives.

checked this - found nothing very specific

> Basically, the MPC8xx processors have a dynamic power management
> system that doesn't gain much from just doing something in the idle()
> loop.  The majority of the power is consumed by peripherals.  If they
> are not enabled, they automatically power down.  All of the MPC8xx
> drivers "do the right thing" on open and close to power up/down
> peripherals.
>
> If you have some very low power standby requirement, you need to add
> lots of power management software to do things like power down/up
> any external peripherals on your board, put DRAM in autorefresh
> mode, shut down the clocks and put the processor into a deep sleep.

yes - thats what i would like to do ;-)

> You could look at some of the PowerMac power management code for
> design ideas.

could anyone be a little more specific to get me to the right files ?

Regards
Gustl

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