Intel GMA 900 (915G) - interlaced modes?

[will]

>Sure. With interlaced mode out of CRTC (instead of TV-out encoder)
>there are no such problems (i.e., no "by luck" things and no constant
>switching due to lost IRQs, the fields can be swapped but that's
>a matter of a single switch - PAL (analog, not DV) normally uses
>top-first, CRTC may do bottom-first as with NTSC).

>Anyway, with interlaced CRTC mode you basically sync to 25 or ~30 Hz
>and things work automatically.

Are you absolutely sure about this? I thought if you had no common frame of
reference then this would not work reliably. I thought that vsync and buffer
swapping occur at the field rate not the frame rate. I tried using an
interlaced mode on the radeon driver and I still had to use the software
de-interlacer to get a watchable picture (perhaps this is a problem with
that driver or my setup though). So even if you want TFF or BFF you may get
the opposite and it may not be a reliable mode of operation. 

I've only ever heard of the Matrox cards as being able to output interlaced
video with the correct field parity and not when used under X as field
parity may not be supported?