On Wed, Jan 02, 2002 at 07:13:26PM -0700, Gordon McNutt wrote: > Looks like DATA OUT toggling on BULK endpoints has a bug
<snip> > >>>>>>> DESCRIPTION <<<<<<< > > This is 100% reproducible, but I'm using an experimental device. The > special property of this device is that it *always* NAKs packets sent > to one of its bulk endpoints (at least it should, but more on that > later...). > > I load a usbserial module built for generic support and give it the > product and vendor to recognize my device. On cable attachment > enumeration proceeds as expected and /dev/ttyUSB0 becomes my device. > I start a CATC trace and on the host: > > $ echo hello > /dev/ttyUSB0 > > As expected, the echo command blocks. After a second or two I kill it > with two Ctrl-C's from the keyboard (for some reason, one is not enough). > The CATC trace shows all the DATA OUT packets containing the data are > NAKd, as expected. The data toggle is 0 for all these packets, as > expected. > > Now repeat the process. This time, the echo command returns immediately. > The CATC trace shows that the DATA OUT toggle bit is now set to 1. The > device ACKd the packet. > > My theory is that the device hardware sees the data toggle of 1 and > mistakenly believes the host lost an ACK and is resending a packet. So > the device ACKs the packet (and probably just discards the data). I'm > not sure how else device hardware can accomodate lost ACKs, so I guess > this is sane behaviour on the part of the device. > > If so, then this is probably a bug in the Linux UHCI driver. If I > understand the spec correctly, the host should not advance the toggle bit > unless the packet was ACKd. > > I've poked around in the code a bit, and I see a couple of places in > uhci.c where the toggle bit is being messed with, but I'm not sure > how my signaling the process is removing the urb. It seems that at > that point the toggle sequence associated with the urb needs to be > canceled unless it was ACKed by the device. > > I don't mean to be impolite, but I do not subscribe to this list. So please > CC replies to [EMAIL PROTECTED] First off, does this also happen with the other UHCI driver (not the "Alternate" one?) When you cancel the "echo" command the urb that has been submitted to the device is canceled. So the host controller driver thinks it is finished. Then when you repeat the "echo" command, a completely new urb is created and submitted to the device. Since the transmission is a new one, I'm guessing that the host controller driver thinks it is ok to toggle the data toggle bit. As for if this is really a bug or not, I'll leave that to the host controller driver authors :) thanks, greg k-h _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
