tw68: Congratulations :-) and possible vsync problem :-(

[Michael <auslands-kv@gmx.de>]

Hello

I have tested a TW6805 based mini-pci card with the new tw68-v2 driver from 
git (22 January 2010).

First of all: Congratulations! It is really working great.

However, I noticed some frame errors here and then. It is not easy to 
identify what the reason is. It looks a bit like a buffer problem as it 
happens more often, if there is some load on the system.

Here is a simple way how I can reproduce the frame errors:

mplayer -framedrop -fs -vo x11 tv:// -tv 
device=/dev/video0:width=640:height=480:normid=3

With this command, cpu load goes to 100% on my low powered geode system. The 
frame errors are very obvious. It looks like a vsync problem as the wrong 
frames always start somewhere in the middle. There is no horizontal shift 
visible.

Reducing the image size:

mplayer -framedrop -fs -vo x11 tv:// -tv 
device=/dev/video0:width=320:height=240:normid=3

gives a drop in CPU load to 13%. No more frame errors.

Also using hardware accelerated video playback (xv) reduces CPU load to some 
20% and removes the frame errors:

mplayer -framedrop -fs -vo xv tv:// -tv 
device=/dev/video0:width=640:height=480:normid=3

Still, even here, occasionally there are some frame errors, depending on 
what happens on the system. These can be induced as follows. Using this 
program: 

mkfifo /tmp/mp
mplayer -framedrop -fs -vf screenshot -vo xv tv:// -tv 
device=/dev/video0:normid=3 -slave -input file=/tmp/mp </dev/null >/dev/null

When this test prog runs, you can issue commands to mplayer, e.g.

echo pause > /tmp/mp

This pauses mplayer. A second

echo pause > /tmp/mp

starts mplayer again. Here the first frame shows the error.

The same happens if you issue:

echo screenshot 0 > /tmp/mp

This captures a screenshot and saves it into the current pwd. Again, when 
mplayer takes the shot, there comes one error frame (probably also wrong 
vsync).


Btw. using instead a bttv based card all these tests run without frame 
errors.

Does this information help to identify and remove the bug?

Best regards

Michael