Re: [LAU] USB audio interface and a buggy USB controller

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To: Philipp Überbacher <hollunder@...>
Cc: linux-audio-user <linux-audio-user@...>
Date: Wednesday, September 15, 2010 - 6:42 pm

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
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Messages in current thread:
[LAU] USB audio interface and a buggy USB controller, Joan Quintana, (Tue Sep 7, 12:19 am)
Re: [LAU] USB audio interface and a buggy USB controller, Clemens Ladisch, (Tue Sep 7, 6:49 am)
Re: [LAU] USB audio interface and a buggy USB controller, Jeremy Jongepier, (Tue Sep 14, 11:24 am)
Re: [LAU] USB audio interface and a buggy USB controller, Clemens Ladisch, (Tue Sep 14, 12:23 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Jeremy Jongepier, (Tue Sep 14, 12:29 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Monty Montgomery, (Tue Sep 14, 4:26 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Jeremy Jongepier, (Wed Sep 15, 7:59 am)
Re: [LAU] USB audio interface and a buggy USB controller, Jeremy Jongepier, (Fri Sep 17, 1:38 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Philipp Überbacher, (Sat Sep 18, 6:58 am)
Re: [LAU] USB audio interface and a buggy USB controller, Jeremy Jongepier, (Sat Sep 18, 11:31 am)
Re: [LAU] USB audio interface and a buggy USB controller, Monty Montgomery, (Tue Sep 14, 5:57 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Clemens Ladisch, (Thu Sep 16, 7:21 am)
Re: [LAU] USB audio interface and a buggy USB controller, Philipp Überbacher, (Wed Sep 15, 6:30 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Philipp Überbacher, (Sat Sep 18, 7:04 am)
Re: [LAU] USB audio interface and a buggy USB controller, Monty Montgomery, (Fri Sep 17, 9:21 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Jeremy Jongepier, (Sat Sep 18, 11:36 am)
Re: [LAU] USB audio interface and a buggy USB controller, Patrick Shirkey, (Sat Sep 18, 7:06 am)
Re: [LAU] USB audio interface and a buggy USB controller, Monty Montgomery, (Wed Sep 15, 6:42 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Clemens Ladisch, (Thu Sep 16, 12:32 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Monty Montgomery, (Thu Sep 16, 8:40 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Philipp Überbacher, (Thu Sep 16, 12:04 pm)
Re: [LAU] USB audio interface and a buggy USB controller, Jeremy Jongepier, (Wed Sep 15, 8:01 am)