[wdmaudiodev] Re: KMDF and AVStream revisited

  • From: Tim Roberts <timr@xxxxxxxxx>
  • To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Fri, 12 Nov 2010 16:26:05 -0800

Daniel Rice wrote:
> Can you point me to some reference on this?

There's really no reference for it.  Filter drivers are not hard to
write, especially with KMDF, and there are sample filter drivers in the
WDK.  Usbaudio.sys speaks kernel streaming out of its top end, and URBs
out of its bottom end.  Both of those technologies are documented.

> Our devices aren't class compliant, ...

As long as you use an isochronous pipe, you can generally rewrite things
to satisfy usbaudio.sys.

> ...have many channels, ...

How many?  I don't know whether usbaudio.sys has a limit.  Doesn't the
spec allow 24?

> ...need to have the lowest latency possible through both WDM and ASIO,...

Well, everybody needs that.  It's not like they specifically designed
usbaudio.sys for high latency.

> ...and need to do DSP processing on the usb completion routine for our audio 
> transfers.

I worked with one company that did acoustic echo cancellation through
this kind of lower filter, by processing the audio after it came back. 
It can be done.  Whether it is the easiest path depends on HOW
non-compliant your device is.

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


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