On Wed, 3 Jan 2007, David Brownell wrote: > On Tuesday 02 January 2007 4:35 am, Phil Endecott wrote: > > Dear All, > > > > How should a gadgetfs application cause an ACK to be sent to the host > > in response to a sucessfully received and processed control out transaction? > > I'm presuming you mean "start the STATUS stage" ... which is not the same > thing as sending an ACK.
He meant "complete the STATUS stage". The host is responsible for starting it, and the device responds with a 0-length DATA1 packet (not an ACK). > The controller acks automatically, and then after > the last DATA stage packet is sent, the STATUS stage is a packet going the > other direction. Until the STATUS stage is acked, the control transfer has > not completed. > > Modulo hardware interface botches which will in at least one case (AT91) > preclude this for gadgetfs, the status stage should start automatically > when all the data has been read. So: issue a read (this is OUT) for > N (>0) bytes, and the underlying controller driver should automatically > start the STATUS stage of the control transfer. This is slightly unfortunate. Section 8.5.3.1 of the USB spec states that the DATA1 packet of a control-OUT STATUS stage shouldn't be sent until the device has completed carrying out the request. But gadgetfs (and probably the controller drivers too) won't wait; it will send the 0-length data packet as soon as the OUT data has been received. > Something to be aware of: not all gadget controller drivers seem to > handle control-OUT transfers correctly ... especially in the "deferred > response" mode needed by gadgetfs. You can test control-OUT transfers > using "usbtest" test case #14; and g_file_storage uses deferred response > mode, but ISTR not for control-OUT transfers. You might be hitting a > controller driver (or controller!) bug specific to that combination... g_file_storage does use control-OUT transfers with non-empty DATA stages when you run it using the CB or CBI transport (that's how each SCSI command gets sent), but then it doesn't use a deferred response. And g_file_storage does use a deferred response for the Bulk-Only Reset and Set Configuration requests, but although they are control-OUT transfers they don't have any DATA stages. So g_file_storage might not be the best test case for these questions. 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
