Developers

The MOD Duo (as of release 1.1) runs Linux, version 3.4, with real time patch.
ALSA is used for the audio driver. JACK runs inside as audio server backend, with mod-host loading each LV2 plugin as a new JACK client as mod-ui as the web server.
There's no X11 or any other kind of graphical interface. In fact, X11 libs are not even available.
SSH is open by default, user 'root' and password 'mod'.

The CPU is a Cortex A7, running at a constant 912 MHz.
The compiler is GCC 4.9, with the default compilation flags being:
-O3 -mcpu=cortex-a7 -mtune=cortex-a7 -mfpu=neon-vfpv4 -mfloat-abi=hard -mvectorize-with-neon-quad

For aggressive optimization, add these:
-ffast-math -fprefetch-loop-arrays -funroll-loops -funsafe-loop-optimizations

Building binaries for the MOD Duo can be easily done using the mod-plugin-builder.

mod-plugin-builder

The mod-plugin-builder is a custom build system that gives developers a similar system to what's available inside the Duo.
We do not recommend the use of a regular Linux armhf system or compiler, it might lead to issues due to mismatching library versions.

If you're running Linux just clone MOD Plugin Builder and follow the instructions.

In summary:

$ git clone git://github.com/moddevices/mod-plugin-builder
$ cd mod-plugin-builder
$ ./bootstrap.sh

This process should take at least 1 hour, probably more depending on your CPU.
Assuming your source code is cross-compile friendly (ie, no hardcoded compiler and paths and uses pkg-config to find extra libraries), the compiler setup is as simple as: (adjust as needed)

$ . ~/mod-plugin-builder/local.env
$ # cmake, waf configure, ./configure, etc
$ make

The local.env file will setup your Linux compiler environment variables (such as CC, CXX, CFLAGS, etc) to use mod-plugin-builder files.
If everything goes well, the resulting binaries will be ARMv7, MOD Duo compatible.

Quick example plugin

A quick example plugin is available inside mod-plugin-builder in make -C plugins/package/eg-amp-lv2/source/, which works with this cross-compilation setup.
See https://github.com/moddevices/mod-plugin-builder/tree/master/plugins/package/eg-amp-lv2/source

Building this example plugin can be done like so:

$ . ~/mod-plugin-builder/local.env
$ make -C ~/mod-plugin-builder/plugins/package/eg-amp-lv2/source

After this the eg-amp.lv2 bundle is ready to be deployed into a MOD unit.

Deploying plugins

We can deploy compiled LV2 plugins to the MOD using MOD-SDK or via command-line using curl.

If you have mod-sdk installed start it up using the target plugin dir as LV2_PATH, like so:

$ export LV2_PATH=~/mod-plugin-builder/plugins/package/eg-amp-lv2/
$ modsdk

Then open a browser at localhost:9000, select a plugin from the list and use the "deploy" tab to push the selected plugin's bundle to the Duo.

For advanced users, you can push a bundle to the mod by running this: (adjust as needed)

$ cd ~/mod-plugin-builder/plugins/package/eg-amp-lv2/
$ tar cz eg-amp.lv2 | base64 | curl -F 'package=@-' http://192.168.51.1/sdk/install

That's it! Your plugin is now inside the MOD!

Linux

Being Linux, developers have access to UNIX and POSIX APIs.
This means <unistd.h>, <pthread.h> and <stdlib.h> for example.

For more information see:

• https://www.kernel.org/doc/man-pages/
• http://pubs.opengroup.org/onlinepubs/9699919799/functions/contents.html

Toolchain

As of release 1.1, the MOD Duo uses:

• GCC 4.9
• glibc 2.21
• binutils 2.25

JACK

Also known as Jack Audio Connection Kit, is the audio server running inside the MOD.
Developers can create JACK clients to interact with the audio data directly (without being managed by a plugin host).

For more information see:

• http://jackaudio.org/api/index.html

NOTE: As of release 1.1, MOD Duo uses JACK2.

LV2

Audio and MIDI plugins in MOD Duo are done in LV2 format.
MOD provides custom LV2 extensions (for MOD specific data and HTML interfaces).

For more information see:

• http://lv2plug.in/pages/developing.html
• http://web1.moddevices.com/shared/ns/mod/
• http://web1.moddevices.com/shared/ns/modgui/

Developer mode

MOD's web interface has some hidden features, not really useful for users but useful for developers.
This includes:

• Buffer size change (128 or 256 frames)
• Install-All button in plugin store
• Network statistics
• Xrun counter

To enable developer mode, open the browser developer console and enter:

   enable_dev_mode()

Starting from v1.3, this setting is saved within the MOD, and developer mode is enabled the next time the page loads.
To disable developer mode, open the browser developer console and enter:

   disable_dev_mode()

Unstable plugins

To see unstable plugins on the plugin store open the browser development console and enter:

   $("#cloud-plugins-stable").parent().show()

NOTE: Do not report bugs when using unstable plugins.
They have not been curated or tested, so they might corrupt memory or even crash.
Use with caution.

Libraries

The following libraries are available inside the Duo:

• acl
• alsa
• armadillo
• audiofile
• boost
• cairo
• dbus
• expat
• fftw/fftwf
• ffmpeg
• flac
• fluidsynth
• fontconfig
• freetype
• gio/giomm
• glib/glibmm
• glibc (v2.21)
• icu
• jack
• libffi
• libgig
• libjpeg/libturbojpeg
• liblo
• libogg
• libpng
• libsamplerate
• libsigc
• libsndfile
• libvorbis
• libxml2
• lilv
• lvtk
• mxml
• ncurses
• ne10
• pcre
• pixman
• python (v3.4)
• qt5 (core, network, sql and xml)
• readline
• serd
• sord
• sratom
• systemd (v219)
• zita-convolver
• zita-resampler

USB Device Support

• Several USB-MIDI devices
• Arduino running MocoLufa firmware (to create midi-controllers)
• PlayStation 3 and 4 Controllers
• Guitar Hero Controller (Red Octane Xbox version)

Hardware Specification

CPU:

• Dual Core ARM A7 1.0GHz
• 4GB Flash Storage, 1GB RAM

AUDIO CODEC:

• Cirrus Logic, 24 bit / 48 kHz AD/DA
• DAC/ADC: 104dB Dynamic Range. -90dB THD+N

CONTROLLER:

• 2 knobs with LCD screen
• 2 foot switches with color LEDs

I/O CONNECTIONS:

• MIDI IN/OUT – Standard DIN 5 pins
• Control Chain – RJ45 connector – for additional controllers
• USB HOST – USB 2.0 Standard-A type, supporting: USB Bluetooth, USB Wifi, USB MIDI
• USB DEVICE – USB 2.0 Standard-B type, supporting: USB Ethernet Connection