Messages in this thread | | | Date | Mon, 17 Oct 2011 20:11:18 +0200 | From | Johannes Stezenbach <> | Subject | Re: [Patch] Increase USBFS Bulk Transfer size |
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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. */
Maybe we should look at the descriptors?
Johannes
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