[App_rpt] USB hubs & USB audio

Sat Jul 26 02:12:40 UTC 2008

David,

Just so you know that it can be done, I used a 7 port USB hub with TT's on
each port and filled it with 7 radio channels running simultaneously for a
commercial trunking radio system and it works just fine.
The server was a 2.66 GHz Pentium 4 on an ASUS motherboard.

73,

Steve Henke, W9SH

On Fri, Jul 25, 2008 at 9:19 PM, David McGough <kb4fxc at inttek.net> wrote:

>
> Hi Everyone,
>
> Well, I just tried one of the usbgear hubs listed below. It ..almost..
> works. The 2 URI devices I'm experimenting with are identified and
> functional EXCEPT that it sounds like the audio sampling rate is
> wrong--way too low with aliasing distortion (or something). ugh. Probably
> a driver confusion issue??
>
> Anyway, the USB hub and hardware otherwise seems to be fine.
> Here is an output from the usbtree utility:
>
> [root at kb4fxc-rpt ~]# ./usbtree
> /: Bus 02.Port 1: Dev 1, Class=root_hub, Drv=ohci_hcd/8p, 12M
> /: Bus 01.Port 1: Dev 1, Class=root_hub, Drv=ehci_hcd/8p, 480M
>    |_ Port 4: Dev 2, If 0, Prod=USB2.0 Hub, Class=hub, Drv=hub/4p, 480M
>        |_ Port 1: Dev 3, If 0, Prod=C-Media USB Headphone Set, Class=audio,
> Drv=snd-usb-audio, 12M
>        |_ Port 1: Dev 3, If 1, Prod=, Class=audio, Drv=snd-usb-audio, 12M
>        |_ Port 1: Dev 3, If 2, Prod=, Class=audio, Drv=snd-usb-audio, 12M
>        |_ Port 1: Dev 3, If 3, Prod=, Class=HID, Drv=usbfs, 12M
>        |_ Port 2: Dev 4, If 0, Prod=C-Media USB Headphone Set, Class=audio,
> Drv=snd-usb-audio, 12M
>        |_ Port 2: Dev 4, If 1, Prod=, Class=audio, Drv=snd-usb-audio, 12M
>        |_ Port 2: Dev 4, If 2, Prod=, Class=audio, Drv=snd-usb-audio, 12M
>        |_ Port 2: Dev 4, If 3, Prod=, Class=HID, Drv=usbhid, 12M
>        |_ Port 4: Dev 5, If 0, Prod=USB2.0 Hub, Class=hub, Drv=hub/4p, 480M
>
>
> I'll investigate further since this is ultimately a config I may want to
> use as well.
>
> David KB4FXC
>
>
> On Tue, 22 Jul 2008, David McGough wrote:
>
> >
> > So, I guess the next question is: Does anyone have a favorite multi-tt
> > hub? ....I have used this one in the past for other linux applications
> and
> > it seemed okay...I'll try one with the URI's....I guess the biggest issue
> > here is that the hub you buy today won't necessarily be the one on the
> > shelves tomorrow....A bit frustrating!
> >
> > http://www.usbgear.com/USBG-217C.html
> >
> > -David
> >
> >
> >
> > On Tue, 22 Jul 2008, David Kramer wrote:
> >
> > > I have successfully tested URIs with several high speed USB hubs.  But
> these
> > > tests were performed without any other USB devices connected at the
> same
> > > time so this may not be very usefull.
> > >
> > > Skip points out the difference between full speed (12Mbps) and high
> speed
> > > (480Mbs) devices.  This terminology is confusing.  Not all USB 2.0
> compliant
> > > hubs support high speed, so be sure the package says HIGH SPEED.
> > >
> > > Very few hubs support multiple transaction translators, probably
> because the
> > > chip sets are more expensive and almost nobody understands the need.
> > > Theoretically, one TT is all that is needed provided you don't mix USB
> 1.x
> > > and 2.0 devices on the same hub.  Keep in mind that USB supports
> several
> > > data modes each with varying priorities and latency allocations.  Plus
> USB
> > > physical layer is half-duplex so one-way communication never comes
> close to
> > > 480Mbps.  The TT tries to handle all the traffic so don't expect good
> > > results if you plug a bunch of web cams or other bandwidth hungry
> devices
> > > into your hub.
> > >
> > > Hope this help.
> > >
> > > David Kramer
> > > DMK Engineering Inc.
> > > 310-544-1222
> > >
> > >
> > > -----Original Message-----
> > > From: app_rpt-bounces at lists.illiana.net
> > > [mailto:app_rpt-bounces at lists.illiana.net] On Behalf Of Skip WB6YMH
> > > Sent: Tuesday, July 22, 2008 1:22 PM
> > > To: app_rpt at lists.illiana.net
> > > Subject: [App_rpt] USB hubs & USB audio
> > >
> > > > Jim Dixon and I have had disapointing results with USB hubs during
> the
> > > > testing of USB fobs with them. We don't know why they don't work
> > > > properly and we don't have the time to figure it out right now. There
> > > > may be hubs which work just fine, but we just don't know as the root
> > > > cause of the problem has not been uncovered.  If Steve Henke W9SH
> > > > knows something I don't them maybe he should speak up on the list.
> > > > Steve  WA6ZFT
> > >
> > > The problem is probably complex.  USB 2.0 hubs come in two flavors
> single-
> > > transaction translators (single-TT) and multi-transaction translators
> > > (multi-TT).  Most USB audio devices are "full speed" devices (12
> > > mbits/sec), not "high speed" devices (480 mbits/sec) so the USB hub
> must
> > > translate the data rate between the host and the device.  The single-TT
> > > devices only have a single translator which is shared between all
> ports.
> > > A multi-TT hub has a translator per port.  So in theory a milti-TT hub
> is
> > > what you should want for optimal bus usage.
> > >
> > > An additional complication is that the Linux kernel must be multi-TT
> hub
> > > aware to properly schedule things.  I'm not current with Linux
> > > development, but I've read discussions in the past about improving the
> > > kernel's USB scheduler in this area.
> > >
> > > Here are a couple of links to info which may be useful:
> > >
> > >
> http://www.commsdesign.com/design_corner/showArticle.jhtml?articleID=1650536
> > > 2
> > >
> > > http://www.linux-usb.org/usb2.html
> > >
> > > 73's Skip WB6YMH
> > >
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