i855crt 0.4 review

by rbytes.net on

i855crt is a userspace driver that should enable CRT out on intel 855GM/GME based laptop. At the moment XFree 4.4.0 (and maybe 4.3.0

License: GPL (GNU General Public License)
File size: 0K
Developer: Andrea Merello
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i855crt is a userspace driver that should enable CRT out on intel 855GM/GME based laptop.
At the moment XFree 4.4.0 (and maybe 4.3.0 and others) includes an opensource driver for this video card, but it doesn't provide any way to manage crt out.

Some other auxiliary driver has been written with the purpose to do that, but none of them worked for me, or worked as i expected. In particular the 'i810switch' driver can enable CRT out but with some limitation.

The main difference between this driver and the i810switch is that the latter simply enables
the DAC and connect it to the same pipe used by the primary video out, while this driver uses two different pipes, one connected to the LVDS (internal LCD port) and one for the CRT DAC.

This has some advantages:

Connecting the DAC to the same pipe of witch the LVDS is connected (always the pipe B in i855) can cause some image corruption. In my case it was dirty and unstable. Using two pipes should solve this issue.
Using two pipe allow to use different refresh rates for the CRT and the LVDS ports.

And some drawbacks:

Using two pipes implies using two planes, one for each pipe, where render the image.
This not cause any performance loss since we can map both the planes on the same framebuffer, however, according to the intel datasheet, it isn't possible to have video overlay on both pipes (at least without SW tricks).

This actually means that you can view your preferred X, gtk or qt program on both LCD and CRT at the same time without any problem, but if you want to see a DVD-player or similar program (that uses video overlay) on both CRT and LCD at the same time you have to do a SW copy of the overlay plane. This can cause performance issues.

by default in the i810 XFree driver HW mouse cursor is enabled. If you want to use HW cursor you need to apply xf86-4.4.0-patch to such driver. (see next chapter). Patching is also required to use overlay routing.

Note that this driver has been tested only on XFree 4.4.0 and intel Montara 855GM/GME on kernel 2.6.4 with vesafb.

In particular a framebuffer driver for 855GM-like exist in kernel 2.4 series, but since it isn't available in 2.6 kernels i have had no way to try if it can co-exist with this driver.

What's New in This Release:
Some code clean-up
i855crt now pay attention to avoid VCO floating during PLL & DAC configuration
registers dump utility added
initial support for Xvideo/overlay
README file updated

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