Re: [tlug] webcam: USB 2.0 controllers

[David Santinoli <marauder@example.com>]

On Tue, Nov 27, 2007 at 07:25:32PM -0500, jep200404 wrote:
> David Santinoli wrote:
> 
> > Other influential factors are the presence of hubs between the PC
> > and the webcams, and - in case of USB 1.1 cams connected to USB 2.0
> > controllers - how is USB 1.1 supported (via a companion controller
> > or a transaction translator).
> 
> How much have you seen USB 2.0 controllers muck up USB 1.1 devices? 
> Is this an issue of _badly_ implemented USB 2.0 controllers? 

The nVidia-based mainboard I'm experimenting with claims to have two
EHCI controllers, but apparently all USB 1.1 devices end up connected to
a single fallback OHCI controller, no matter where they are plugged in
physically.  It might be a design choice rather than a bug, but it's
quite dysfunctional.  (Drivers, too, are likely to play their perverted
role - plugging and unplugging cameras in certain sequences may result
in a _negative_ total bandwidth reserved for isochronous transfers.)

Cheers,
 David
-- 
 David Santinoli
 Tieffe Sistemi S.r.l.                      viale Piceno 21, Milano
 www.tieffesistemi.com                         tel. +39 02 45490882