[pxc] pxc reading frames- correction

[Alessandro Rubini]

Hello.

> I really want to know if there are any possibility of grab the images in
> a non-interlaced manner in the frame buffer,  of way,   of read just 1
> field in 20 ms (without wait for the second one), instead of read the
> entire frame and spent 40 ms to read it.

Early versions of the driver delivered whatever field was available at
time of reading. Then I fixed this misbehaviour, and now you always
get the same field (always even, or always odd, I don't
remember). This feature is required for many motion detection
applications, to avoid the half-pixel flickering.

>From comments in dma.c::px_write_dma_program it looks like this fix
was contributed by Chanop Silpa-Anan.

Please note that you can change the behaviour, but it's not completely
trivial. With the redesigned (and much better) buffer-management
introduced some time ago, each and every buffer has the same DMA
program, and the next buffer to be used is selected on an
image-by-image basis. If you want both even end odd buffers, you need
slightly different DMA programs for the two of them, thus making it
difficult the run-time selection of the next buffer.

Every problem is solvable, but this is not a trivial one, actually.

/alessandro
-- 
Alessandro Rubini, free software specialist.
Device drivers, embedded systems, courses.
http://ar.linux.it/