AVOption vs FireWire video

[matt connolly]

I read somewhere here that the AVOption is super smart ( and I don't doubt that it isn't ) because the ABVB board accesses the SCSI accelerator directly. This leaves the rest of the PCI bus free for Pro Tools. Does this happen only in a 9600 and the PT / AV boards on different bridges? Can it also happen in a 3-slotter with an expansion chassis with PT / AV boards on different bridges? Where else?

Is is also possible then, for FireWire to have the same advantage by using a FireWire drive to store the information?? ie: Quicktime instructs the data to come off the FireWire drive and go directly to the FireWire video device, thus not using up main PCI/RAM bus bandwidth??

[Digi Engineering]

Good question Matt. The ABVB board has very large frame buffers so it is possible to transfer video data directly from the SCSI accelerator to ABVB as a bus mastered transaction. Because of the tiered nature of PCI if you put the ABVB behind the same PCI bridge that traffic is effectively hidden from the rest of the bus. That will occur whether it is on a separate bridge in a 9600 or in an expansion chasis.

I'm not sure whether what you described with Firewire is possible or not. To my knowledge none of the Firewire drives can act as bus masters. Also, QT wants to be able to display a window of the DV video at all times so the video must make its way to host memory.
-Mike Rockwell

[matt connolly]

Thanks Mike. I assume that the advantages of the ABVB-SCSI host direct communication is then lost in a 3 slot mac because they will be on the same PCI bus.

I thought it was possible for QT4 to stream from a FireWire drive directly to a FireWire device, with only the control information coming from the CPU. AFAIK, with FireWire and USB there is only ever one bus master, and that is the CPU.

But then if it has to be on the screen, it surely is coming into main memory. Maybe they do it like the old Miro cards, and the QT window on the mac is just gray....??

Interesting times, heh?