On Wed, 20 Sep 2006, Harald Welte wrote: > Hi! > > I'm currently writing a USB device firmware for a Free Software / Free > hardware project based on an AT91SAM7 (see http://www.openpcd.org/) > > In order to implement USB DFU (device firmware upgrade), I need support > for "big" control out transfers (larger than the 8 byte control endpoint > size). I suppose this is a rarely used feature, since most control > transfers are used to read information from a device (control in > transfers). > > When I use libusb / usbdevio on a 2.6.17.13 kernel to send a control out > transfer of e.g. 256 bytes, then I expect it to create 32 usb data out > packets of each 8 bytes size, plus one zero-length packet to terminate > the transfer. I'm using usb_control_msg() to do the transfer. > > However, on the AT91SAM7 I only see the 32 usb data out packets, and no > ZLP (zero-length-packet). > > Transfers of an non-modulo-eight size (e.g. 31 packets of 8 bytes, plus > one four-byte packet) work perfectly fine, since in this case no ZLP is > supposed to be at the end of the transfer. > > The host controller is UHCI in this case. > > Am I somehow assuming something wrong? Is there anything at all on the > host software stack that controls the generation of a ZLP at the end of > the transfer, or is this all done by the host controller?
Your assumption is wrong. When a control-out transfer takes, the host controller sends a SETUP packet followed by as many OUT/DATA packets as necessary to transfer the data, but no zero-length OUT/DATA. There is a zero-length IN packet to terminate the transfer (the "status stage"), but that's present regardless of the amount of data. The idea is that you don't need a zero-length packet to terminate the data stage of the transfer, since the status stage's IN packet will always mark the termination. For bulk-out transfers you can force an extra zero-length packet at the end (if the data size is > 0 and divisible by the maxpacket length) by setting URB_ZERO_PACKET in urb->transfer_flags. That works only for bulk-out, not for control-out. Alan Stern ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
