Simulating a lower resolution on the OLPC XO Laptop

Jordan Crouse jordan at
Tue Nov 25 11:37:51 EST 2008

Bert Freudenberg wrote:
> 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.

Indeed.  I think there is a DCON interaction happening, because the 
mouse gets "corrupted" during upscaling as well - and that implies that 
the issue is happening after the screen is constructed.  The upscaling 
works fine on a CRT and on a "standard" TFT panel, so that is what leads 
me back to the DCON.  Its also a long shot that the 1200x900 resolution 
is confusing the scaler, but I doubt it since the aspect ratio is still 
4:3.  I would love for other people to try the driver (it is in the 
latest debxo, I think); perhaps you can see the pattern that I can't.

> 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 ...

The RGB video overlay should just work (TM).  So it would take less of a 
determined X hacker, and more of a determined application hacker to put 
all the pieces together.


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