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@lists.illiana.net> > [mailto:
app_rpt-bounces@lists.illiana.net] On Behalf Of Skip WB6YMH
> > Sent: Tuesday, July 22, 2008 1:22 PM
> > To:
app_rpt@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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