[pulseaudio-discuss] Headset support

[Pali Rohár]

On Wednesday 04 April 2018 16:47:57 David Woodhouse wrote:
> I've now counted three types of headset control that we should support,
> ideally through a consistent interface.
> 
> 
>  • The first is Bluetooth HFP/HSP for which support is already present 
>    and just needs to be connected up.
> 
>  • Second is the USB HID devices, including most "Skype for Business"
>    certified headsets. I have a Pidgin plugin which drives these 
>    directly, but it would be better for PulseAudio to open the HID 
>    device for itself and for the controls to be associated with the
>    specific hardware.
> 
>  • Third is the Android/etc. 3.5mm jack where button presses are
>    implemented as short-circuit or specific resistances from the mic
>    pin to ground:
>    https://source.android.com/devices/accessories/headset/plug-headset-spec
>    The Linux kernel has support for these (at least for a few codec 
>    chips), and they appear as events on an input device along with the 
>    jack insertion/removal events. Which I note we also don't support in
>    PA yet? Although there were patches in 2011 at 
>    https://www.mail-archive.com/pulseaudio-discuss@mail.0pointer.de/msg09830.html
> 
> 
> Are there any more?

Nokia ECI headsets - 3.5mm jack with bi-directional ECI bus on MIC bias.
In most cases those headsets contain buttons, but ECI bus supports also
some memory read/write operations. But IIRC it is not possible to use
them with ordinary sound cards (activating MIC bias is too slow for ECI)
and Nokia implemented ECI protocol in their phones at ASIC level, some
translation of ECI to I2C. ECI protocol itself is undocumented, but I
saw some images from oscilloscope from which protocol could be decoded.

Other Nokia headsets (non-ECI) - again 3.5mm jack, but supports only one
button press. Maybe similar to your "third" one.

Bluetooth A2DP with AVRCP - but this should be already supported.

-- 
Pali Rohár
pali.rohar at gmail.com
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