DireWolf with ALSA Loopback Devices
===================================

As part of poking around with Packet setups,
I wanted to be able to easily test things by running two DireWolf instances communicating locally.

Unfortunately while DireWolf can use a UDP socket or ``stdin`` for *input*,
it will only output to a sound device.

Fortunately we can fake sound devices,
thanks to `ALSA's snd-aloop <https://www.alsa-project.org/wiki/Matrix:Module-aloop>`_

(This is all on Debian GNU/Linux; you can probably do something similar on macOS with Loopback / BlackHole; I have no idea about Windows)

Basic setup and testing
-----------------------

* ``sudo modprobe snd_aloop`` to load the ``aloop`` driver per https://www.alsa-project.org/wiki/Matrix:Module-aloop
* ``aplay -l`` and ``arecord -l`` should show you now have the relevant ``Loopback`` devices
    * You may need to install ``alsa-utils`` if you don't have ``arecord`` or ``aplay``
    * The devices (I think that's the right term?) are of the format ``Loopback,X,Y`` where Y is the subchannel; audio from ``0,Y`` is output to ``1,Y`` and vice versa
* ``gen_packets -o x.wav`` (packaged with ``direwolf``) will produce you some test packet data in ``x.wav`` 
* ``atest x.wav`` will check the test data you just generated

Then to actually test transmission:

* In one session ``arecord -D plughw:Loopback,1,0 -f cd y.wav`` to start recording to ``y.wav``
* In another session then ``aplay -D plughw:Loopback,0,0 x.wav`` to play the test data
* Terminate the ``arecord`` once ``aplay`` has finished
* Then verify received data with ``atest y.wav``
    * Sometimes I lose the last packet here - haven't quite figured out why
    * This probably isn't entirely correct/optimal in terms of channel and quality etc. but it works Well Enough

DireWolf setup
--------------

A basic test setup looks like:

.. code-block:: ini
   :linenos:
   :caption: direwolf0.conf

    # Input 0,1 Output 1,0
    ADEVICE plughw:Loopback,0,1 plughw:Loopback,1,0

    # Explicit AGW/KISS ports to not conflict
    AGWPORT 5000
    KISSPORT 6000

    # Send some periodic test data
    MYCALL XXXXX-10
    CBEACON delay=0:10 every=0:10 info=0

.. code-block:: ini
   :linenos:
   :caption: direwolf1.conf

    # Input 0,0 Output 1,1
    ADEVICE plughw:Loopback,0,0 plughw:Loopback,1,1

    # Explicit AGW/KISS ports to not conflict
    AGWPORT 5001
    KISSPORT 6001

    # Send some periodic test data
    MYCALL XXXXX-11
    CBEACON delay=0:10 every=0:10 info=1

You can then run these with:

.. code-block:: shell

    # Session 0
    # Run direwolf dumping packets, with text colours off, reporting audio stats every 30s
    $ direwolf -dp -t 0 -a 30 -c direwolf0.conf

    # Session 1
    # Run direwolf dumping packets, with text colours off, reporting audio stats every 30s
    $ direwolf -dp -t 0 -a 30 -c direwolf1.conf

And you'll have two DireWolf instances beaconing at each other through your loopback audio interfaces!