Re: Frames come in bursty when capturing with low framerate

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On Fri, 12 Dec 2003, Tuukka Toivonen wrote:
> On Fri, 12 Dec 2003, Erik Slagter wrote:
> 
> >> That's what I used before, and that works ok. The problem is that I'm using
> >> 4 or more grabbers in one PC now, and capturing everything and skipping
> >> frames causes too much data on the PCI bus, resulting in image distortion.
> >> (distorted horizontal lines at random places, etc)...
> >Yeah typical... You might try to play with card latency's, but probably
> >you're just plain out of PCI bandwidth.
> 
> Latency? Is there some BIOS setting or how it can be changed?

Usually a bios setting, but you can also change it with setpci at run time.  I
wrote some more about this a while back, check the list archives.

> And by the way, why wouldn't PCI bandwidth run out temporarily with just
> one card, if several devices try to transfer data at once? What PCI does in

The capture card has a buffer that will fill up while it waits for access to
the PCI bus.  If it has to wait too long, the buffer fills and you lose data.

> this case, allow one device to transfer one word, then the next, and so on,
> or is the bus allocated for a single device for a longer period?

The latter.

> My single TV card (bttv878) makes the horizontal garbage as described if I
> use SCSI disk simultaneously, no matter whether synchronous or async mode
> or whatever transfer speed the SCSI controller is set, or how small image
> I'm capturing. (IDE works fine).

What scsi card is it?  It might be a poorly designed card, or a poorly
designed driver.  You might also have the latency on the scsi card set too
high, letting it hold the PCI bus for too long.




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