On 19 Nov 2016 18:48, "Marek Marczykowski-Górecki" <
[email protected]> wrote:
>
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> On Sat, Nov 19, 2016 at 06:27:05AM -0800, Eric Shelton wrote:
> > Although I do not have a current working solution (the main workaround I
> > have heard discussed is passing through a USB controller and using a USB
> > audio device), there are a few development possibilities I wanted to
note:
> >
> > (1) Windows PV audio drivers from OpenXT
> > (https://github.com/OpenXT/xc-windows/tree/master/xenaud).  This might
> > provide most of the framework needed to implement a Qubes-compatible PV
> >
> > (2) Linux stubdom + QEMU emulated audio device.  This might be a
convenient
> > way to get audio working in all HVMs (Windows, Linux, etc), since QEMU
> > provides a number of options for emulated devices (ES1370, AC97, Intel
HDA,
> > and others).

These drivers are a tiny bit iffy, as only PulseAudio and ich9 seem to work
well in Windows.

It requires extra environment variables to be passed to qemu, such as more
often audio interrupt and smaller buffer for low latency. I also had
problems setting it to output 32-bit depth in Windows.

That said, given real-time configured PulseAudio server (in a real-time
configured sound vm) it can deliver latencies low enough for recording
monitoring on KVM (increase scheduler granularity) and on Xen with rtds
scheduler. Getting stubdom to set up correctly required some scripting.

Make sure to enable threadirqs in the host and that VM. (kernel boot
option)

You can have more than one device and each shows up as a separate stream.
Surround sound is supported.

> > (3) Xen upstream PV audio support.  There have been several attempts and
> > renewed attempts at implementing a "sndif" in mainline Xen (once a
> > candidate feature for Xen
> > 4.6:
https://lists.xenproject.org/archives/html/xen-devel/2015-05/msg00129.html,
> > recent xen-devel
> > discussion:
https://lists.xenproject.org/archives/html/xen-devel/2015-05/msg00129.html).

Sorta works but is Xen only.

R.

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