USB MIDI2 device
Overview
This sample demonstrates how to implement a USB MIDI device. It can run on any board with a USB device controller. This sample sends all MIDI1 messages sent to the device back to the host. In addition, presses and release on input keys (such as the board user buttons) are sent as MIDI1 note on and note off events.
The application exposes a single USB-MIDI interface with a single bidirectional group terminal. This allows exchanging data with the host on a “virtual wire” that carries MIDI1 messages, pretty much like a standard USB-MIDI in/out adapter would provide. The loopback acts as if a real MIDI cable was connected between the output and the input, and the input keys act as a MIDI keyboard.
Building and Running
The code can be found in samples/subsys/usb/midi.
To build and flash the application:
west build -b nucleo_f429zi samples/subsys/usb/midi
west flash
Using the MIDI interface
Once this sample is flashed, connect the device USB port to a host computer with MIDI support. For example, on Linux, you can use alsa to access the device:
$ amidi -l
Dir Device Name
IO hw:2,1,0 Group 1 (USBD MIDI Sample)
On Mac OS you can use the system tool “Audio MIDI Setup” to view the device, see https://support.apple.com/guide/audio-midi-setup/set-up-midi-devices-ams875bae1e0/mac
The “USBD MIDI Sample” interface should also appear in any program with MIDI support; like your favorite Digital Audio Workstation or synthetizer. If you don’t have any such program at hand, there are some webmidi programs online, for example: https://muted.io/piano/.
Testing loopback
Open a first shell, and start dumping MIDI events:
$ amidi -p hw:2,1,0 -d
Then, in a second shell, send some MIDI events (for example note-on/note-off):
$ amidi -p hw:2,1,0 -S "90427f 804200"
These events should then appear in the first shell (dump)
On devboards with a user button, press it and observe that there are some note on/note off events delivered to the first shell (dump)
$ amidi -p hw:2,1,0 -d
90 40 7F
80 40 7F
90 40 7F
80 40 7F
[...]