On Monday 27 December 2004 6:44 pm, Nigel Roberts wrote: > I see in the konicawc > driver (which has a similar set up) that this is some how related to > the frame rate that the camera produces, with a smaller packet size > resulting in a lower frame rate. Is this a standard way of doing > things? > > This doesn't really make sense to me, I keep thinking that a smaller > packet size will only mean that there are more packets per second, or > is this a fixed rate for USB?
For isochronous transfers there are two key variables: - Interval between transfers. It's a log2 encoding, and for full speed it's almost always 1/msec. High speed can do up to 8/msec. - Size of the transfer. For full speed this is up to 1023 bytes per transfer; high speed can do up to 1024 bytes per transfer, or for "high bandwidth" modes up to 3 times that. So there are several ways to grab a given amount of bandwidth; 1024 bytes every other msec, 512 bytes each msec, 64 bytes every uframe ... all the same bandwidth. For video, the size of a frame (and whether it's compressed or not) is also a factor. Bandwidth in KB/sec divided by KB/frame gives you frames/sec, for uncompressed data. Some cameras support multiple frame rates. - Dave ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
