[pulseaudio-discuss] HSP as Audio Gateway

[Pali Rohár]

Hi! Just note... it is not related to HSP/HFP profiles, but maybe it
could be interested for you. For A2DP profile there are some codecs
(e.g. FastStream of aptX Low Latency) which support backchannel used for
microphone voice -- so these codecs are bi-directional. Support for
FastStream (it is just SBC codec with fixed parameters) including
backchannel is in my patch series sent to this list for extending A2DP
codec support.

On Thursday 31 January 2019 12:04:28 diego.ml wrote:
> Hi all,
> 
> I have two Linux embedded boards with kernel 4.9, and recent Bluez (5.50) and pulseaudio (12.2). At the moment I've elected to keep ofono disabled to keep things simple, so just HSP without HFP.
> 
> I want to connect them for testing purposes using HSP: my target is to play an audio sample on one side (board #1) and record it at the other side (board #2). The same test  is already working using A2DP, so I can transmit (paplay) and receive (parec) high quality audio between the two boards.
> If I understand correctly what I need to do is to connect the two boards using HSP, using Audio Gateway role on one side and Headset role on the other side.
> Unfortunately if I look at "pactl list cards" output:
> https://pastebin.com/8pkTCNya
> I see that both boards have "headset_head_unit available yes" and "headset_audio_gateway available no".
> 
> Does the role selection depend on Bluez settings? (E.g. the class of the device specified in /etc/bluetooth/main.conf) Or does it depend on some pulseaudio setting?
> 
> Currently I've read:
> https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User/Bluetooth/
> https://gavv.github.io/articles/pulseaudio-under-the-hood/#bluetooth-backend
> https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User/Modules/#index36h3 (this seems a bit outdated)
> and source code of the bluetooth policy module:
> https://gitlab.freedesktop.org/pulseaudio/pulseaudio/blob/master/src/modules/bluetooth/module-bluetooth-policy.c
> but I still don't have a clear picture.
> 
> So my target is: connect two Linux PC and transmit audio between them using HSP (or HFP with ofono).
> 
> Any help is really appreciated.
> 
> Thank you,
> Diego
> 
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-- 
Pali Rohár
pali.rohar at gmail.com