On Tue, 26 Sep 2006, Vivek Dharmadhikari wrote: > I used the patch provided by Alan to increase the no. of retries. The > patch caused the ohci hardware to retry the command 4 times in a row > instead of 3 times.
For some strange reason, the OHCI specification document doesn't say exactly how the retry mechanism should work. There is a 2-bit error counter, normally set to 0. It gets reset to 0 every time a transaction succeeds. When a transaction fails the counter gets incremented, unless it is already equal to 2, in which case the host controller returns an error. The spec doesn't say what should happen if the counter is initially equal to 3. Normally you would expect it to just stay there, with no change, no errors reported, and unlimited retries. But apparently your hardware "increments" it to 0, giving a total of 4 attempts instead of 3. > So the host controller is willing to talk to device > but the device appear to be dead. Actually the device is not dead. Not at all. If it were then the class-specific device reset (which is nothing more than a USB control transfer) would fail. But it doesn't fail; it succeeds and the device continues operating. Until the command is retried... I think it's significant that the device always fails at exactly the same spot. That is, one particular command causes the failure. It could be that the device doesn't want to carry out the command -- but we know that it _does_ carry out the command when running at full speed or using a self-powered high-speed hub. More likely the bit pattern of that command string is, for some reason, not received correctly by the device. Maybe it thinks there's a bit-stuffing violation when there really isn't. However this is sheer speculation. We don't really have enough information to say why it doesn't work. IMO you should just accept that this is hardware problem which can't be solved in software and won't get better, and either use that self-powered hub all the time or else use a different brand of flash memory device. 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
