On Wednesday 16 February 2005 12:01 pm, Roman Kagan wrote: > On Wed, Feb 16, 2005 at 09:01:11AM -0800, Srdjan Sobajic wrote: > > > They're bulk, one in, one out. However, on Windows the API for > > accessing bulk and interrupt endpoints is the same, while you have a > > different API for ISO and control.
That's not exactly true ... there are only URBs. Though there's extra wierdness for ISO, since those URBs offer per-packet control and status reporting. > Unless I'm misenterpreting the specs, that's not an artefact of Windows > API but rather the inherent similarity of bulk and interrupt transfers: > basically the only difference is scheduling. More or less true ... though interrupt transfers also seem to have a "toggle optional" mode usable to synchronize some ISO transfers. > BTW the sanity checks added to usbfs handlers in 2.6.11 seem to allow > exactly the opposite behavior, i.e. both bulk and interrupt URBs on > interrupt endpoint, and only bulk URBs on bulk endpoints: > > ... > > Is that intentional, and I need to go reread the specs? That's intentional. The issue is that the hardware associated with interrupt endpoints may not tolerate being polled more often than specified in the descriptor, so that's prevented. As you observed, such scheduling _is_ the basic difference... Whereas the "singleshot" interrupt transfer notion is a bit of a historical API glitch. The normal 2.6 way to do such a thing is issue the usual interrupt URB and than not resubmit it in its completion handler. But in 2.2 and 2.4 USB, the resubmission was "automagic" ... and the usbfs userspace API adopted that model. So "singleshot" requests had to go in some other way ... and that way was sending a bulk URB to an interrupt endpoint. We didn't elect to change that yet; eventually the replacement of usbfs should fix that botch. - Dave ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
