Required components

To support shared audio in a QNX Hypervisor system, you must add components to your guest and host images, and configure the virtio-snd vdev in the guest's VM.

The host may offer each guest different audio functionality, just as if each guest were running on its own separate board. For example, one guest may be allowed to capture and output audio, while another is allowed only to output audio.

To present audio functionality in the host to any specific guest, you configure the virtio-snd vdev in the VM that hosts the guest. The vdev configuration specifies which PCM streams on the host are exposed to the guest. It also specifies any restrictions to audio parameters that must be applied to the guest, such as sample rates, supported formats, and minumum and maximum fragment sizes. See “vdev virtio-snd” for details.

Host components

To enable the audio framework, you must have the following components on your host:

the audio drivers (deva-*) that you would use for audio when running the QNX Neutrino RTOS on your target board
the host audio service (io-audio) to provide the guests and host applications access to audio capture, playback, and management features
an audio device configuration file (e.g., io-audio.conf) that configures the audio devices for the host
an audio management configuration file (e.g., audio_policy.conf) that configures the audio policy for the host (optional)
the vdev that provides access to audio functionality, virtio-snd. The vdev module, vdev-virtio-snd.so, must be included in the shared object list of your hypervisor host buildfile.
for each VM that hosts a guest that needs to use audio, the virtio-snd vdev is configured; for information on how to do this, see “vdev virtio-snd”
the path to the configuration file (*.qvmconf) for each guest that's running in a VM is included in your hypervisor host buildfile

For general information on how to configure your hypervisor host, see the “Configuration” section of the QNX Hypervisor User's Guide.

Guest components

Because the virtio-snd vdev is a para-virtualized device, a guest must have a VirtIO sound driver that can communicate with the vdev.

Managing access to physical devices by multiple entities

If a PCM device owned by the host has to support concurrent playback on multiple guests, you must configure a software mixer for the device. This mixer is enabled by default, but it may be disabled (or specifically enabled) via the startup instructions for the io-audio service in the host, when the hardware driver is mounted, or through the audio policy configuration file, io_audio_*.conf.

Similarly, if concurrent capture through the same PCM device (in the host) is required, a software splitter must be configured for the device.

Finally, if the host also needs to play and/or capture audio through a PCM device that it makes accessible to guests, the host must have a software mixer and/or splitter to manage concurrent playback and capture.

For more information about the io-audio service, and support for software mixers and splitters, see the Audio Developer's Guide. See also the io-audio entry in the QNX Neutrino Utilities Reference.