Thinking Kernel Mode

{ Not invented here }

Unless I scribble this down somewhere, I will forget. So let me dump my memory . . 

Kernel Streaming is a fairly complicated topic. And to study this, the available resources are the DDK help documentation and the samples. AFAIK, there are no books written on this topic. And what is present online is also meager. 

The Streaming Devices (Video & Audio) subsection of the DDK help, has everything documented.

Now,  in order to emulate a virtual audio hardware, we have to write an Audio Miniport Adapter driver. The MSAVD sample source code can be used for this purpose.

WHDC Audio Device Technologies for Windows [http://www.microsoft.com/whdc/device/audio/default.mspx] 

Getting Started with WDM Audio Drivers [http://www.microsoft.com/whdc/device/audio/wdmaud-drv.mspx]

This is how the audio device stack will look like. 

The Adapter Driver is what we write and for a virtual audio device it will be a modified MSAVD driver. 

Modifying the MSAVD Driver to make your own virtual audio device.

In Kernel Streaming, every component is a Filter. Filters have input (sink) and output (source) pins. Data enters a filter through its input pin and leaves through the output pin. Every filter has a purpose :  to process the data flowing through them.

As an audio device (virtual or real), your hardware will have a range of audio data parameters which can be accepted. Or in other words, only data complying to a specific format and parameter range can be accepted by the input pins. This is called the property of the pin. 

Specify those ranges in the PinDataRangesStream static variable of the MSAVD source code. 

Now, in the WaveCyclic miniport there are two methods named CopyTo and CopyFrom for copying audio data to and from the audio device's  memory (DMA). Add code to those function to implement a virtual write and read and the minimal audio driver code is complete.