On Sat, Dec 20, 2003 at 04:30:29PM +0100, Erik Slagter wrote:
> > When I watch TV in Linux using 2.6.0 and bttv (tvtime, but it happens in
> > all tv-playing applications so it's a driver issue), there is a severe
> > tearing effect. Like horizontal brown lines scanning and the text
> > "shakes" and "jumps." Imagine having vsync set wrong in a game from the
> > 1999 era -- it's like that, and very obnoxious. The tvtime people were
> > very helpful but could not think of any solution and we tried every
> > deinterlacing idea that could be conceived.
>
> This looks like a PCI bus mastering problem. I've had it too. Because
> the TV cards bus mastering ("DMA") engine cannot get access to the PCI
> bus within a certain time (usually 10 - 40 ms) the buffer pipe get
> overrun. This pipe is usually only a hundred to thousands of bytes
> large.
>
> The solution may be to increase the latency time of the capture card
> (look for an option "latency" in your tv card's drivers). If you can set
> it using the BIOS, then also set the latency for the other cards and
> possibly integrated devices as low as possible.
>
> If all this doesn't help, you either have a motherboard with broken PCI
> implementation (not that rare...) or the hardware of the PCI bus is too
> slow. I had this problem very severely on a 486/133 with a UMC chipset.
> I had it very mildly on a MSI motherboard with an athlon xp 2000. Now
> with my Tyan motherboard and dual athlon xp 2600 it's gone altogether.
>
> BTW if I enable energy saving for Athlon MP chipsets (don't know the
> name of the kernel option from the top of my head), this effect also
> shows.
>
>
> --
Thanks for your suggestion, Erik. You tipped me off to a long-shot
theory that turned out to be CORRECT! The problem is solved. Naturally,
since this list is archived, it's important for me to specify why.
I had this being issued on boot-up:
'setpci -v -H1 -s 0:0.0 95=1e'
This was an old trick I read about on Gentoo's boards which enables some
sort of CPU cooling/HLT commands. I don't understand enough about how
PCI or BIOS stuff works to bother trying to make this option co-exist
with my bttv setup (I issue a similar command from Windows and it
doesn't cause problems). I'll deal for the time being with the higher
CPU temperature. The difference is extreme, but it's worth it
considering the problems this command was causing.
I am not completely satisfied with the image, but it is no longer jerky
screen-wide and I *believe* I can blame the rest on the simple fact that
cable isn't beautiful. Removing that command on boot-up has given me a
stable image and re-issuing it gives me an unstable image, so there is
no doubt that it was the culprit.
Thanks,
- Cody
