USB2VGA adapters on XO-1.5 (and XO-1 with F11 images)

[Martin Langhoff]

On Wed, Jul 7, 2010 at 5:06 PM, Martin Langhoff
<martin.langhoff at gmail.com> wrote:
> Updated olpc-usbvgamirror with tweaks for better performance.

For monitors/projectors that can handle 800x600 or 1024x768, the VNC
approach is the best we can do.

For monitors/projectors that can handle something close to 1200x900 --
1152x864, you can use Xinerama instead. Here is an xorg.conf that does
exactly that:

http://dev.laptop.org/~martin/usbvga/xorg-xo1.5-dcon-hires-extmon.conf

It is *much* faster than VNC, and plays well with suspend (you'll
still want to disable aggressive powersaving).

Limitations and notes:

 - Needs to be "switched on" at X startup time. olpc-configure could
check at boot time if sisusbvga is loaded and change the xorg.conf
symlink.

 - It clips the margins of the desktop. But not very much, if the
projector honours the resolution, it's minimal. (Funny enough, if we
use 1280x960 but try to constrain it with Virtual, X ignores our Modes
line and falls back to 1152x864.)

 - It hides the cursor -- this is a long-standing Xinerama "mirror mode" quirk.

 - It isn't super fast, but the performance is acceptable. (We are
saturating the USB 2 bandwidth with the amount of pixels and the
bitdepth -- but cannot scale down either.)

 - Video (via Xv) doesn't work on USB2VGA devices

cheers,


m
-- 
 martin.langhoff at gmail.com
 martin at laptop.org -- School Server Architect
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