[alsa-devel] Stuttering 100mA and 500mA MaxPower usb audio investigation on bus powered and external powererd usb hubs

[Takashi Iwai]

At Sun, 09 Nov 2008 16:55:31 +0100,
Jelle de Jong wrote:
> 
> Jelle de Jong wrote:
> > Hello everybody,
> > 
> > I have been testing several scenarios to find some glues why some usb
> > audio devices did not fully work and gave stuttering sounds I found the
> > following:
> > 
> > usb devices define a max power attribute during there enumeration
> > process. I have some usb devices that have this at 500mA and some that
> > have this on 100mA.
> > 
> > I also have some usb hubs that have external extra power supply and some
> > that are only a hub with bus power.
> > 
> > Here it comes:
> > 
> > Make sure the 4 port usb hub is full with for example:
> > - usb keyboard (100mA)
> > - usb mouse (100mA)
> > - usb audio (100mA or 500mA)
> > - usb stick (200mA/500mA)
> > 
> > - usb hub with external power (500mA MaxPower) (AC adapter delivers 1A)
> > - usb hub without external power (100mA MaxPower)
> > 
> > Make sure to use audio with several tones low tones (most dvds will do)
> > 
> > When connecting a 100mA usb audio devices on a hub with external power
> > it will give stuttering sound!! (most usb audo devices are 100mA and
> > most hubs are external powered due to more then one usb stick)
> > 
> > When connecting a 500mA usb audio device on a hub with external power it
> > will work perfectly.
> > 
> > When connecting a 100mA or a 500mA usb audio device on a hub without
> > external power it will work perfectly.
> > 
> > I have the idea there is something wrong with the power distribution
> > system when using external powered usb hubs...
> > 
> > Any ideas how to correctly address this problem/bug?
> > 
> > Best regards,
> > 
> > Jelle
> >
> 
> I did some more debugging, it think the 100mA/500mA behavior is just an
> effect of the real problem the usb isochronous audio bandwidth under
> Linux is doing some things that make usb audio not working very well.
> 
> I wanted to be able to use 4 usb audio device on one usb at the same
> time. using a powered usb hub this gives shuttering sound. What are the
> max usb bandwidth limits on Linux?
> 
> I also found out that the only what that all usb audio device work is to
> connected them directly without any hub between them. This takes up a
> lot of resources.
> 
> Would somebody have to possibility to take a good look at the usb audio
> issues with multiple devices and isochronous transfers?

These look more like a general USB bandwidth problem / question than
USB-audio specific.  I'd suggest you to ask this rather on USB devel ML.


thanks,

Takashi