Re: [RFC v5 1/8] audio: Move tel drivers to DBus interface

Hello Luiz,

Le 17/12/2011 11:15, Luiz Augusto von Dentz a écrit :

quoted

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Good work putting this together, probably we should add this to the
documentation, btw this already shows us the latency won't be that
great with this solution.

Thanks
Which solution is not great ? both ?

Both have problems, endpoint add extra round trips per connection
which can be a problem for audio transfer/SCO reconnections.

OK, So I will continue with "Transport path" proposal.

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Currently, if I take volume speaker as sample, BlueZ sends
SpeakerGainChanged signal on reception of SetSpeakerGain method call (user
action on the phone) or AT+VGS command (user action on headset).

This signal should only be sent by the Media Transport object, i.e. :
  - for "Transport path" proposal, this signal should be moved
        from headset.c to transport.c.
  - for "Media Endpoint" proposal, this signal should be moved
        to the Media Transport of the telephony agent.

I do not understand why a ping-pong effect should start (no application
should react to SpeakerGainChanged signal by a SetSpeakerGain method call).

Yep, IMO the gains/volume need to be moved to transport, btw both
agent and endpoint need to react to events such as volume change, the
agent need to send AT+VG commands and the endpoint notify the
application when the volume change completes.

In case of Telephony agent implementing the Audio Gateway part of HSP/HFP, it will send a +VG unsolicited result, which will not get reply from the Headset.
So, endpoint will not be able to notify the application when the volume change completes.

Now, I don't think it is impossible to handle this it is just tricky
and we cannot detect errors easily, but volume changes is already
tricky (see PulseAudio), so I think it might be fine to try this first
and see the results.

OK

quoted

Not yet, but your are right this test should be removed.
We must make it possible to set Noise Reduction, Echo Cancellation, speaker
or microphone gain values before the audio is connected.
Those values should be stored in the Media Transport object.

Whenever you give the transport object you have to give permission to
the agent, but don't simplify let any process changes those values.

OK, I will add Telephony agent to the test.

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True, but are you sure the agent wont have to deal directly with the
SCO connection? Afaik there were some AT commands to do the audio
transfer, although for HFP it seems to be directly by
connecting/disconnecting SCO.

My understanding is that BlueZ/oFono are not involved in decision to set-up
or not the SCO connection, this decision should be taken by PulseAudio or a
policy manager component, and SCO connection will be performed on Acquire
method called by PulseAudio.

Audio transfer is both ways, but apparently there is no AT command for
triggering it, iirc it was part of HSP spec, but I don't think we have
to worry too much about HSP nowadays.

OK

Regards

Fred

-- 
Frederic Danis                            Open Source Technology Center
frederic.danis@intel.com                              Intel Corporation