Simulating a lower resolution on the OLPC XO Laptop

Bert Freudenberg bert at
Tue Nov 25 09:11:27 EST 2008

On 25.11.2008, at 11:57, Strider wrote:

> Hi,
> I have a XO Laptop which is a nice machine machine with a high res  
> display of 1200x900 pixels. The problem with this is that the laptop  
> isn't powerful enugh to handle fullscreen applications at this  
> resolution. If only the display could switch to a lower resolution  
> things would be much better but it seems that this laptop only  
> supports a single resolution.
> So I was wondering if it would be possible of simulating lower res  
> at a low level, that is the xf86-video-geode driver.
> I'm not an expert in video drivers but i imagine that there are  
> functions to request a pixel to be drawn on screen based on what's  
> in the video ram.
> Now let's say that it's not one pixel but two that we put on screen,  
> and that we draw each lines two times. That would result in a  
> 600x450 resolution.
> If we do the same thing but repating the operations three times , we  
> would have a 400x300 resolution.
> Some emulators have a scale option to do such a thing and manage it  
> quite well, but if we had such an option in the video driver, the  
> result would be even faster !
> So what do you think about this? Is it possible ?

The Geode actually can do real upscaling (that is, scale multiple  
graphics resolutions to the panel resolution), it works fine on other  
machines and LCDs. But latest word is that this somehow interacts  
badly with our DCON, so no-one has gotten it to work correctly on the  
XO yet.

There still may be hope, because the video upscaler can take RGB 5:6:5  
data, so in theory a lower-res 16 bpp frame buffer could be upscaled  
on-the-fly (and the upscaler does 30 fps easily). But I guess getting  
this to work would require a very determined X hacker ...

- Bert -

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