USB buses [was: Re: [linux-audio-user] maudio quattro...]

[Sampo Savolainen]

Hi,

It does look like that you have two busses. Actually root hub would be a
more exact term.

I guess you understand this, but for general education:
 - Soundcards need to stream small bits of data ALL THE TIME
 - Hard drives burst (comparatively) HUGE chunks once in a while. 
This kind of operation does not mix well (=at all), when the streaming
data has to received on time and with low latency.

This incompatibility has nothing to do with bandwidth, it's a limitation
of serial interfaces. It's not about doubling your bandwidth, it's about
having two independent communication channels.

After sounding like I know about this stuff, here is something I don't
understand:
 - I have four usb controllers visible with lspci. 
   3 UHCI (USB1.1) and 1 EHCI (USB2) controllers.
 - cat /proc/interrupts shows that there are three usb-uhci modules
   and one ehci module, each module using a different IRQ. 
 - With lsusb -v I see that 3 root hubs are "USB UHCI Root Hub" and one
   is "Intel Corp. 82801DB USB2".

This looks like all USB2 devices are connected to this hub. That means
that there is a strong possibility that at least in my systems, all USB2
devices would share the same hub, regardless of which usb jack the
device is plugged into. I do not know how this works out in the driver
level, but it looks quite suspicious.

Does anyone have better knowledge about this? Could you enlighten us?


 Sampo


On Thu, 2004-06-10 at 22:00, Frank Barknecht wrote:
> Is there a way to find out how many buses there with things like
> lsusb? Or being concrete again: Does this output mean, that I have two
> busses, that should be able to provide the double bandwidth?
> 
> $ /usr/sbin/lsusb 
> Bus 002 Device 001: ID 0000:0000  
> Bus 001 Device 002: ID 0547:1002 Anchor Chips, Inc. 
> Bus 001 Device 001: ID 0000:0000  
> 
> This would be interesting as I might consider using some data
> intensive devices on one bus while the other is taken by the
> soundcard.
> 
> Ciao