On Tue, 24 May 2005, stef wrote: > On Tue, May 24, 2005 at 01:18:59PM +0200, stef wrote: >> On Mon, May 23, 2005 at 02:52:27PM -0400, m. allan noah wrote: >>> steven, i see this exact problem with certain fujitsu scanners. the >>> difficulty is that USB uses a 0/1 toggling bit during the data transmit >>> phase. when libusb closes the device, the device should reset the toggle >>> back to 0, the kernel does. subsequent transmissions should start with >>> toggle set to 0, but if device thinks it should be 1, then device ignores >>> packets. windows never closes the device (the driver loads at bootup) so >>> the fujitsu engineers had no idea what i was talking about (though i note >>> that later usb2.0 fujitsu scanners do not have this problem) >>> >>> you have three options that i see: >>> >>> 1. count the number of data packets you >>> are sending to scanner, and always send an even number. remember that just >>> cause you sent or read 16 k of data, does not matter, it was busted up by >>> lower layers. you need this larger number of smaller packets. >>> >>> 2. get kernel/libusb to keep current toggle instead of trashing it. >>> >>> 3. call usb_reset(device) as the very last step before you exit. this will >>> cause the device to re-enumerate, and reset all of its internal data. >>> while ugly, this works for me everytime. there are other functions like >>> usb_clearhalt and usb_resetep, but those dont seem to fix my problem. >>> >>> my advice? write a little prog that uses libusb directly, and try to do >>> simple things outside the confines of sane. >>> >>> allan >>> >> >> Hello, >> >> this is really interesting. I had an intermittent hangup with the >> genesys backend, depending of tha amount of scan data. I just couldn't >> figured out why. Now, with your explanation, it does make sense. >> Dependending on the number of bulk reads, the toggle wasn't set like it >> should. So I did like you suggest: call usb_reset(device) before closing the >> device in sane_close(). That got rid of the hang (at least on HP2300C, need >> to double check for MD6471). >> Now my question is : would it be OK to do it in a backend ? Is there >> any drawback ? >> >> Regards, >> Stef >> >> -- > > OK, > > after some tests I can confirm that genesys hangs are related to the > 'toggle' and that usb_reset() fix this. But unfortunately, resetting affects > all devices plugged in the usb ports: if I plug 2 scanners on the same pair > of USB ports, launch 2 xsane, then leave on -> bus is reset, and the left > xsane can't work since it's device has also been reset. > > Well, I guess it's time to count data packets .... > > Regards, > Stef
odd, i have not seen my system reset the entire bus, but maybe i was not watching closely enough. under kernel 2.6, the device should keep the same ids, but under 2.4, the id will change. this can be a problem if you dont re-scan the bus after the reset. did you try the other libusb functions like resetep and clearhalt? may work for you. allan > > -- "so don't tell us it can't be done, putting down what you don't know. money isn't our god, integrity will free our souls" - Max Cavalera
