This change introduces a new feature to the mobile application -
audio I/O support, which allows the user to speak right from the
host side running mobile through its ordinary mic and speakers.
The audio I/O is based on libosmogapk [1][2], which in its turn
uses the ALSA sound system for the playback and capture. This
is a new optional dependency of mobile, which is automatically
picked up if available during the build configuration. Whether
to depend on it or not can be controlled using '--with-gapk-io'.
The API offered by libosmogapk implies to use the processing chains,
which generally consist of a source block, several processing blocks,
and a sink block. The mobile app implements the following chains:
- 'pq_audio_source' (voice capture -> frame encoding),
- 'pq_audio_sink' (frame decoding -> voice playback).
both taking/storing TCH frames from/to the following two buffers:
- 'tch_fb_ul' - a buffer for to be played DL TCH frames,
- 'tch_fb_dl' - a buffer for encoded UL TCH frames.
The buffers are served by a new function gapk_io_dequeue().
[1] https://gitea.osmocom.org/osmocom/gapk/
[1] https://osmocom.org/projects/gapk
Change-Id: Ib86b0746606c191573cc773f01172afbb52f33a9
Related: OS#5599