Supporting Auxiliary Audio Devices

Kernel-mode drivers that support auxiliary audio devices can use the auxiliary audio message dispatcher, SoundAuxDispatch, provided by soundlib.lib. If you use soundlib.lib, the amount of customized code a driver needs to provide is minimal. If the hardware provides a mixer, then soundlib.lib calls the mixer’s HwSetControlData and HwGetControlData functions to control volume (see MIXER_INFO). If the hardware does not provide mixer hardware, the driver needs to include a HwSetVolume function for the auxiliary audio device, to control volume (see SOUND_DEVICE_INIT). A DevCapsRoutine is the only other function you need to provide (see SOUND_DEVICE_INIT).

To use soundlib.lib for handling auxiliary audio devices, you must:

• Within the driver object received by DriverEntry, assign SoundDispatch to be the driver’s main dispatcher for IRP control codes. See “Examining_DriverEntry in sndblst.sys.”

• Define a SOUND_DEVICE_INIT structure. The structures’ DispatchRoutine members must be set to the address of SoundAuxDispatch, which is the auxiliary audio dispatch routine within soundlib.lib for DeviceIoControl messages.

• Call SoundCreateDevice once for each SOUND_DEVICE_INIT structure you have defined.