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

[Jelle de Jong]

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?

Thank in advance,

Jelle