Synchronizing Two or More Streams
The SetDmaEngineState routine sets the state of one or more DMA engines to one of the following: running, paused, stopped, or reset. If a call to this routine specifies more than one DMA engine, then all of the DMA engines make the state transition synchronously.
The ability to synchronize a group of streams is required for some audio applications. For example, an audio driver might use codec-combining to create a logical surround-sound audio device that joins two audio codecs: one codec drives the front speakers and a second audio codec drives the back speakers. Depending on the capabilities of the codecs, the audio driver might be required to split the original surround-sound audio stream into two streams, one for each codec. By using the SetDmaEngineState routine to start and stop the streams in unison, the two streams can remain synchronized.
Allowing the two streams to fall out of synchronization by even a few samples might cause undesirable audio artifacts.
The SetDmaEngineState routine is available in both versions of the HD Audio DDI.
The UAA HD Audio class driver does not perform codec-combining.