RE: [Xen-users] Re: XEN sound emulation locks device exclusively

["Csillag, Kristof \(GE Healthcare, consultant\)" <Kristof.Csillag@xxxxxx>]

After checking the source code of ioemu (which is responsible for the audio 
emulation),
I can see that there is a whole fully configurable audio system, with multiple 
output 
backands, including alsa output. (This whole stuff comes from QEMU.)

So it should be possible to send the sound to alsa via the normal channels,
using the dmix plugin.

So the question is: how can I configure the audio sub-system in qemu-dm?
How can I pass parameters to it?
(If I can not, then there should be a mechanism for that.)

     Kristof Csillag


-----Eredeti üzenet-----
Feladó: Petersson, Mats [mailto:Mats.Petersson@xxxxxxx]
Küldve: 2006-11-13, H 16:15
Címzett: Csillag, Kristof (GE Healthcare, consultant); 
xen-users@xxxxxxxxxxxxxxxxxxx
Tárgy: RE: [Xen-users] Re: XEN sound emulation locks device exclusively
 
 

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Csillag, Kristof (GE Healthcare, consultant)
> Sent: 13 November 2006 07:42
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] Re: XEN sound emulation locks device exclusively
> 
> > As I think XEN has no "audio emulation", there's probably 
> no fix other than
> > using VMware that has an audio emulation.
> 
> OK, so I have the wrong idea about how XEN handles sound.
> (I found no documentation on this, so it was basically a guess.)
> 
> Here is what I know:
> 
> - In the notebook computer there is and Intel HDA sound card.
> - In the configuration file for my HVM guest, I have "soundhw='sb16'".
> - The WinXP running as HVM guest sees a Sound Blaster 16 
> sound device, and can use it.
> 
> Here is what I thought:
> 
> - Either the XEN hypervisor, or some user-space tool 
> (probably the later) emulates
>   the hardware interface of a SB16 for the HVM host, and
> - it relays the sound to the sound system of DOM0.
> 
> If this is not how it goes, then what?
> I thought that since there is no real SB16 in the host in question,
> the SB16 interface must have been emulated,
> but from what you say I seem to be mistaken.
> 
> Could someone please explain this, or give a link to the 
> appropriate documentation?

If it's a HVM guest, the sound emulation is done in QEMU-DM, the device
model for the HVM mode. 
In fact, qemu-dm is responsible for ALL hardware emulation with a few
exceptions (timer and interrupt controller functionality) that for
performance reasons are in Xen itself. 

So, yes, qemu-dm will have a SB16 type emulation layer that then
forwards the sound to be played to the real hardware. 

I would expect that this happens at a very low level, so it's "bare
samples" being sent to the hardware, which may mean that it needs to
lock the device exclusively to prevent other streams from interacting. 

--
Mats

> 
> Thank you:
> 
> 
>      Kristof Csillag
> 
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> 
> 
> 




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