On 04/07/2010 02:25 PM, Steve Calfee wrote: > Hi David, > > You are correct that ehci allows up to 20K in one qTD transfer. The > gotcha is it requires that the page be aligned on some big boundary, I > don't remember if it is 4K or something else, but it is a large > alignment requirement. So most ehci host drivers limit a qTD to a 16K > xfer so that there is no alignment issue; that is any transfer from > any address will always fit in the 5 memory ptrs in the qTD hardware > structure if the xfer size is <=16K. Ironically, a linux guest (Fedora Core 12) is what sent me down this path. A USB storage device is passed to the guest and I see a lot of 16k requests, and an occasional 20k request. David -- 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
