More advanced power savings (rev. the DPMS extension).

Jim Gettys jg at
Wed Aug 2 13:47:22 PDT 2006

On Sun, 2006-07-30 at 22:19 +0200, Egbert Eich wrote:

> Is the OLPC switching between two framebuffers?

Yes; in the case of the Geode, it has RAM based integrated graphics.

Our DCON chip has a megabyte of DRAM to hold (at 6 bits/pixel) the image
that was last generated by the Geode, allowing us to power off the Geode
partially, or entirely.

> But regardless - point is, Jim mentioned that it
> takes two frame times to wake up the chip according
> to Jim. 

On wakeup, you have to wait for for two things:
  1) stabilization of the video from the Geode
  2) vertical retrace to occur.
At that point, you can tell the processor's video to go again, tell the
DCON to just pass through the video, and avoid visible glitches will

This timing "dance" will be interesting, but we have a line counter to
let us get the timing right.  Worst case might be two frame times; it
may be less.  We'll see how long 1) actually takes.
                                - Jim

Jim Gettys
One Laptop Per Child

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