Power Management

[Jim Gettys]

On Fri, 2007-06-08 at 15:55 +0100, Richard Hughes wrote:
> On Fri, 2007-06-08 at 10:51 -0400, Ivan Krstić wrote:
> > Richard Hughes wrote:
> > > • When system idle for > 30 seconds we turn the screen off
> > 
> > Remember that we have a DCON that acts as a hardware frame buffer. The
> > screen turning off if you don't use the machine for 30s is a terrible
> > user experience and absolutely not an option
> 
> Sure.
> 
> >  -- but the screen freezing
> > after the same timeout, and springing back to life if you press a button
> > or move the mouse, is more or less how we envisioned this would work all
> > along.
> 
> What's the power difference between freeze and off? If it's not
> substantial, I totally agree with you.
> 

This is pretty much working in Adam's latest work.

Having the DCON take over lets us turn off:
	1. the video drivers
	2. the video unit of the geode
	3. the memory accesses that 2. requires
	4. the GPU.

When the video unit is turned off, the geode nicely turns off the clock
in that part of the chip.  If the gpu isn't being used, it also powers
itself down.

It also lets us drop the frame rate to the LCD.

Switching to and from DCON driving the LCD only takes 20-40ms.
                            - Jim



-- 
Jim Gettys
One Laptop Per Child