[pulseaudio-discuss] alsa ucm in pulseaudio

[Feng Wei]

2011/10/14 David Henningsson <david.henningsson at canonical.com>:
> On 10/14/2011 09:39 AM, Feng Wei wrote:
>>
>> 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.
>
> There is also the "Use Case" concept in UCM, Is there always exactly one
> verb for every use case? If not, one might wonder if "Use Case" or "Verb" is
> what should correspond to the "Profile" concept.
verb is equal to use case. "use case" is a concept and verb is in the
source code.
>
> Card, Sink/Source, Profile and Port are the core concepts in PulseAudio. I
> think UCM should use alsa-sink, alsa-card and alsa-source, but the rest of
> the stuff: pa_alsa_profile_*, pa_alsa_path_*, pa_alsa_mapping - in short,
> everything in alsa-mixer.h, I don't think the UCM implementation should
> touch them. They are too tightly coupled with the existing ideas of how to
> map ALSA kcontrols to Profiles and Ports, something that UCM does in its own
> way. So in my opinion, you should forget about mappings - it's Profile and
> Port (and Sink/Source) we need to match against.
Actually we must map the concepts because ucm is designed for abstract
the complicated kcontrol. In my mind, if we use ucm in pa, the
original profile configuration files and mixer configuration files
will be replaced by ucm configuration files.
>
> As for ports, this again depends on what is mutually exclusive and what
> could be used in parallel, I vaguely remember "Modifiers" as something that
> could be used in parallel with existing streams, if so, they need to be
> separate sinks/sources.
>
>>> 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.
>
> Hmm, for every sink/source, there can only be one active port at a time.
> Also, ports on the same sink/source can be changed on the fly without
> restarting the stream. Does this fit with the description of a UCM "Device"?
As my example described, ucm device is more abstract than physical
device. mutually exclusive ucm device "speaker" and "headset" may
refer to same alsa device "hw:0,0", the only difference is the mixer
route. I'm not sure how to implement the active port switching, if
mapping port to modifier, it should call ucm enable/disable modifier,
but it's more reasonable to call ucm switch device in concept.
>
> --
> David Henningsson, Canonical Ltd.
> http://launchpad.net/~diwic
>



-- 
Wei.Feng (irc wei_feng)
Linaro Multimedia Team
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