[wdmaudiodev] Re: Reg: USB Audio class 2.0

  • From: Tim Roberts <timr@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Thu, 03 Dec 2009 09:38:31 -0800

swarna jakka wrote:
> Actually my question is that i am developing an USB Audio class 1.0,
> and using USB 2.0 device.
> This device is operating in Full speed mode only and i am able to
> operate Audio class1.0 in full speed only and not in High speed mode.
> Enumeration is going to be completed in High speed mode but     i
> can't play audio file in High Speed.
> But the  device using will operate in High speed as well as Full speed.

Your message is confused.  If you are enumerating as high speed, then
you are operating in high speed mode.  If you can only support full
speed, then your device should enumerate in full speed.

The key limitation of usbaudio.sys is that it cannot drive an
isochronous pipe that does more than 1 request per frame.  There are
several ways to meet that requirement.  One is to go full speed, and set
the isochronous interval to 1.  The other is to go high speed, and set
the isochronous interval to 4 (meaning 1 packet every 8 microframes). 
Your device would not see any difference in the two -- the throughput
will be the same.

Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.


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