On Mon, 17 Oct 2011, Johannes Stezenbach wrote: > On Sat, Oct 15, 2011 at 03:04:28PM -0400, Alan Stern wrote: > > On Sat, 15 Oct 2011, Johannes Stezenbach wrote: > > > > > It would make a difference if the > > > device violated the spec and sent 188 byte packets. However, the > > > spec says a short packet terminates the transfer. But I wonder > > > if this is really the case? > > > > The device does not send short packets. If it did, the 24064-byte > > transfers would end early. > > Re-reading the USB-2.0 standard, a short packet which terminates > the transfer is defined by packet_size < wMaxPacketSize, > not by packet_size < 512. > Thus wMaxPacketSize == 188 (or 2*188) might be possible. > > There is a comment in linux/drivers/usb/host/ehci-q.c: > > /* The USB spec says that high speed bulk endpoints > * always use 512 byte maxpacket. But some device > * vendors decided to ignore that, and MSFT is happy > * to help them do so. So now people expect to use > * such nonconformant devices with Linux too; sigh. > */ That comment referred to devices with wMaxPacketSize = 1024, which has been seen in the wild. But other bizarre sizes are possible. > Maybe we should look at the descriptors? It won't hurt, although I would be quite surprised to see anything other than 512. Markus, can you post the output from "lsusb -v" for this inflexible webcam? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
