Excerpts from Monty Montgomery's message of 2010-09-15 20:42:53 +0200: > USB 1.1 audio devices tend to stress the available bandwidth due to > the way the isochronous mode is designed. It makes them 'special' in > many ways, and this is one of the cases the Linux EHCI scheduler > wasn't designed to handle at all, and has simply been hacked here and > there to add support or 'improve' things without actually fixing the > design problems. When I offered a fixed version, there was relatively > little interest in accepting it (it needed a shakedown and debugging > period; big change). The Linux USB stack design is highly unusual in > several fundamental ways, and it complicates the problem (it would be > a very elegant design for completely async/demand driven devices like > mice, so on, it falls flat for fixed bandwidth devices). > > To be fair, the EHCI design is fraught with complexity and serious > races, and even the good drivers like the one in MacOSX have special > hacks for dealing with audio devices (this is assuming the MacOSX > driver is the same as the one used in Darwin. It appears to be from > protocol sniffing. The Darwin driver has several unique scheduling > properties, like putting all the interrupt queue heads up front...). > > At this point, I despair Linux USB ever being reliably workable for > USB1.1 audio devices. The kernel devs really do not believe there is > any problem. Perhaps things will be a little better for the USB 2.0 > audio class once it becomes more common, if it ever becomes common. > > Unfortunately, things seem to be repeating themselves-- isochronous > devices do not work at all on the new 3.0 ports (XHCI). > > Monty Thanks Monty for the insight. Sadly I understand little of the technical side of things, but what it tells me is that I better stay away from audio over USB in future and choose something like expresscard instead. PCI is still the best way to go, right? -- Philipp -- "Wir stehen selbst enttäuscht und sehn betroffen / Den Vorhang zu und alle Fragen offen." Bertolt Brecht, Der gute Mensch von Sezuan _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
