[LAU] Cracking sound via USB (ALSA urb.c:480: frame 5 active: -18)

[Clemens Ladisch]

Ken Restivo wrote:
> On Wed, May 25, 2011 at 08:55:48AM +0200, Jeremy Jongepier wrote:
> > http://lists.linuxaudio.org/pipermail/linux-audio-user/2010-June/070353.html

That bug in Intel's Rate Matching Hub would corrupt audio data, but
is unlikely to result in error messages from the driver.  (Iso packets
have no error correction; corrupted data is just silently ignored.)

> > So not mixing USB1 and USB2 devices but mixing a device performing
> > Full-Speed isochronous-out transactions with a device performing
> > asynchronous transactions. I've tested my Edirol UA-25 with this chipset
> > too and no matter what I tried, full duplex wouldn't work.

The Linux high speed support is somewhat buggy; this affects full
speed devices connected to high speed hubs.

The Rate Matching Hub is internally organized as a high speed hub.

> Wait, what?
> 
> I've been doing way too much reading of USB specs (and the hub.c,
> message.c, and musb driver source code) for work lately, and even though
> I'm definitely suffering from early onset of Alzheimer's, I distinctly
> remember reading that Isochronous and Bulk endpoints were only allowed
> at High Speed (480Mbps).
> 
> At Full speed (12Mbps), IIRC, you get Interrupt and Control endpoints,
> and that's pretty much it.

Iso/bulk are forbidden only at Low speed (1.5Mbps).


Regards,
Clemens