eMIDI

MIDI library optimized for beeing used on embedded devices

This library is in a usable state but not recommended for productive use yet! Most events are not supported yet and the API meight break at any time

Overall Design Goals

• The main target are microcontrollers with very limited ressources

• Robust design / does not behave undefined on malformed or broken MIDI files

• Implementation is done after MIDI 1.0 specification

• Minimum code footprint (configurable by #define)

• Minimum RAM footprint (configurable by #define)

• MIDI file gets not loaded into memory but gets streamed

• A lock free buffer cache which is filled while playing to avoid real time issues on playback

• No use of dynamic memory (malloc and free), just static memory

• Simple abstraction layer, so the library can be ported to any platform easily

• In a later development state MIDI files can also be created. This allows implementing a simple sequencer for example.

Implemented features so far

• Opening and closing of MIDI files and validation of header.
• Reading of all midi events of any midi0 file (data bytes of some events are ignored)
• Support of running status events
• Non-Blocking MIDI player
• Supported channel events
  • NoteOff
  • NoteOn
  • Control Change
  • Program Change
  • Pitch Bend
• Supported META events
  • End of Track
  • Set Tempo
  • Midi Port
  • All other events are ignored in first iteration and will be supported later

Planned

• A cache for the MIDI player to avoid playback timing issues due to slow media access
• Creation of MIDI files
• Support of MIDI 1 files
• MIDI 1 to MIDI 0 converter
• "Compression" - Use running status events plus Note-On with zero velocity for Note-Off

Contraints

• Only little endian platforms supported

Using on Arch Linux

Development and testing is done using Arch Linux. Even this library is targeted for embedded devices it can also be used on non-embedded devices like windows and linux.

Build

Just execute Make

You will find some examples in utils directory:

• dump: dumps all events of a MIDI file
• player: plays a MIDI file using fluidsynth
• gcode: converts a MIDI0 file into gcode, so it can be used for playing music on a CNC mill or 3D printer. (Under development)

To play a MIDI file just execute

bin/player tests/midis/cdefgabc_0.mid

If you get an error like:

Error: cannot open /dev/sequencer

You might need to install fluidsynth first:

Install fluidsynth

sudo pacman -S fluidsynth

Install a soundfont

sudo pacman -S soundfont-fluid

Setup daemon for MIDI playback

sudo vim /etc/conf.d/fluidsynth 

Replace the contents by:

SOUND_FONT=/usr/share/soundfonts/FluidR3_GM.sf2
AUDIO_DRIVER=alsa
OTHER_OPTS='-is -m alsa_seq -r 48000'

Enable and start the fluidsynth daemon

Create a file at

~/.config/systemd/user/fluidsynth.service

You meight create the systemd/user directories first!

Insert the following content:

[Unit]
Description=FluidSynth launched in server mode
After=sound.target

[Service]
ExecStart=/usr/bin/fluidsynth -a pulseaudio -m alsa_seq -i -l -s -p FluidSynth /usr/share/soundfonts/FluidR3_GM.sf2

[Install]
WantedBy=default.target

Execute:

systemctl --user start fluidsynth.service
systemctl --user enable fluidsynth.service

If /dev/sequencer is not showing up you also meight execute:

sudo modprobe snd-seq-oss

And let is start on each boot by opening

/etc/modules-load.d/modules.conf

and adding:

snd-seq-oss