Logitech Webcam USB Standards

[Steve Sisak]

At 5:08 PM -0700 5/5/08, Paul wrote:
>"Logitech QuickCam PC Video Cameras are designed to work on either 
>Universal Host Controller Interface (UHCI) or Open Host Controller 
>Interface (OHCI) implementations of the Universal Serial Bus (USB) 
>standard."
>
>My Sonnet Tango 2.0 FireWire/USB card assigns the AppleUSBEHCI 
>driver according to System Profiler so Logitech's USB 2.0 cameras 
>won't work with Sonnet's PCI cards. I haven't found a fix for that 
>yet but if I find one I'll let you know. I've written Sonnet about 
>it but they wrote back and referred me to Macintouch.com to get 
>support for their product.

I think the documentation on Logitech's site is out of date and 
hasn't been updated to reflect reality -- _all_ USB 2.0 controllers 
are EHCI.

Here's are the possible types of USB controllers:

  UHCI (Universal Host Controller Interface)
  OHCI (Open Host Controller Interface)
  EHCI (Extended Host Controller Interface)

UHCI was Intel's first (1.0) specification -- it's got serious 
performance issues* and we never had to deal with it on the Mac until 
the first Intel Macs shipped with Intel USB controllers.

OHCI is the much-improved USB 1.x controller interface that everyone 
but Intel uses -- Apple skipped directly to OHCI and it's what you 
will encounter on all PPC Macs and nearly all add-in cards.

EHCI is the USB 2.0 specification that everyone uses for high speed 
-- however an EHCI controller will also emulate one or more UHCI or 
OHCI controllers for full speed (as in not high speed) devices.

One thing you might try is adding a high quality, powered USB 2.0 hub 
between the card and camera and see if that makes any difference.

Also, which camera are you using, and what is the misbehavior?

If you see flashes of green in the image, that means that Isochronous 
data is being lost somehow (a zeroed video buffer ends up green if 
interpreted as YUV, where it would be black in RGB).

That could be as simple as a bad cable of connector.

-Steve

-- 
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Steve Sisak, CTO                                 steve.sisak at ioxperts.com
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