On Wednesday 10 November 2004 13:23, Alan Stern wrote: > David: > > http://bugme.osdl.org/show_bug.cgi?id=3480 > > Can you look at this? It seems to be an error in the EHCI bandwidth > reservation. The relevant parts are the second and third attachments.
I've called it a "limitation" of that code; for now, that's how it's expected to behave. I posted a patch to partially resolve that issue in summer 2003 but nobody > There's a high-speed 4-port hub attached to an EHCI controller, with a > full-speed USB camera plugged into the external hub. The camera uses an > interrupt pipe (8-byte maxpacket, 1 ms interval) to transfer command > status, but we're getting -ENOSPC. The "limitation" being that if a given periodic schedule slot already has an entry (say a hub's status IRQ, period 256 msec) then the code refuses to try to schedule anything else (say, the camera's wasteful period 1 msec period). This is unfortunately not as easy to solve for EHCI as it is for any full speed HCD. (EHCI, OHCI, SL811, etc). Not only does scheduling need to look at the bandwidth that's used, but it also needs to consider (a) transaction translator bandwidth, in "TT-per-hub" and "TT-per-port" variants, with (b) TT collisions, where the TT isn't using bandwidth during a microframe but is still unusable because its buffer is tied up with another transaction, and most annoyingly (c) up to four different types of entries in the periodic schedule, each with different hardware and software offsets for the relevant "next entry" TD pointer. That last bit can easily get oopsy. I've dribbled much of that infrastructure into the kernel already, but what I haven't made time to do is dust off the remnants of that 2003 patch, update it, and retest. On the plus side, it's taken quite a while for problem reports to show up ... :) - Dave > > Alan Stern > > ------------------------------------------------------- This SF.Net email is sponsored by: Sybase ASE Linux Express Edition - download now for FREE LinuxWorld Reader's Choice Award Winner for best database on Linux. http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
