[pulseaudio-discuss] alsa ucm in pulseaudio

Feng Wei feng.wei at linaro.org
Fri Oct 14 07:39:01 UTC 2011


2011/10/14 David Henningsson <david.henningsson at canonical.com>:
> On 10/14/2011 04:47 AM, Feng Wei wrote:
>>
>> Hi Liam, Mark, Colin, and all,
>>   I study the codes in pulseaudio and alsa ucm patch recently, and
>> create a page of my study result. I appreciate your feedback. The page
>> is at
>> https://wiki.linaro.org/WorkingGroups/Middleware/Multimedia/Specs/1111/AudioIntegration/UCMPulseAudio/Analyzation.
>>   Also if needed, I'm glad to contribute to the integration of alsa
>> ucm in pulseaudio.
>>   Thank you.
>
> Oh, nice diagrams :-) Some of them might be useful additions to the
> PulseAudio wiki.
Thanks :-)
>
> I think the modelling of UCM concepts onto PulseAudio concepts is an
> important discussion. In PulseAudio, profiles are mainly connected to device
> strings, how to open the devices, channels supported, whereas ports are just
> alsa mixer kcontrol changes. UCM verbs, as I understand it, contain both.
My understanding is profile:port and verb:device/modifier are both
hierarchical. e.g. we have an alsa device string hw:0,0, and some
mixer controls for route speaker or headset. In pa profile, we
describe a profile output:analog-stereo with two ports, one for
speaker, and the other for  headset. In ucm, we define verb "hifi" and
two excluded devices speaker and headset, both of the devices have
PlaybackPCM hw:0,0. And we can also define two modifiers to switch
between speaker and headset. So we can create profile by verb and
create profile input/output mappings by devices(merge the same hw
device) and create ports by modifier. I'm not sure if it break the
original ucm concepts, but I think it can work.
>
> In this context, I have a question: Can more than verb be active at a time
> for a specific card (e g can both "hifi" and "record" be active for the
> panda), and if so, how is it described in UCM what verbs that can coexist
> and which ones are mutually exclusive? I believe PulseAudio is going to need
> that information in order to be able to know how to create its profiles.
In current alsa ucm implementation, only an active verb is permitted,
but it can have more than one devices enabled. In my mind, in "hifi"
mode, we can still record something because we have some devices
(playback or capture) available.
>
> --
> David Henningsson, Canonical Ltd.
> http://launchpad.net/~diwic
>



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Wei.Feng (irc wei_feng)
Linaro Multimedia Team
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