samples: subsys: usb: midi: add new sample

# SPDX-License-Identifier: Apache-2.0

cmake_minimum_required(VERSION 3.20.0)

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})

project(usb_midi)

include(${ZEPHYR_BASE}/samples/subsys/usb/common/common.cmake)

FILE(GLOB app_sources src/*.c)

target_sources(app PRIVATE ${app_sources})

# Copyright (c) 2024 Titouan Christophe

# SPDX-License-Identifier: Apache-2.0

# Source common USB sample options used to initialize new experimental USB

# device stack. The scope of these options is limited to USB samples in project

# tree, you cannot use them in your own application.

source "samples/subsys/usb/common/Kconfig.sample_usbd"

source "Kconfig.zephyr"

.. zephyr:code-sample:: midi

   :name: USB MIDI device class

   :relevant-api: usbd_api usb_midi input_events

   Implements a simple USB-MIDI loopback and keyboard 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 :zephyr_file:`samples/subsys/usb/midi`.

To build and flash the application:

.. zephyr-app-commands::

   :zephyr-app: samples/subsys/usb/midi

   :board: nucleo_f429zi

   :goals: build flash

   :compact:

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:

.. code-block:: console

  $ 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:

.. code-block:: console

  $ amidi -p hw:2,1,0 -d

Then, in a second shell, send some MIDI events (for example note-on/note-off):

.. code-block:: console

  $ 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)

.. code-block:: console

  $ amidi -p hw:2,1,0 -d

  90 40 7F

  80 40 7F

  90 40 7F

  80 40 7F

  [...]

/*

 * Copyright (c) 2024 Titouan Christophe

 *

 * SPDX-License-Identifier: Apache-2.0

 */

/ {

	usb_midi: usb_midi {

		compatible = "zephyr,midi2-device";

		status = "okay";

		#address-cells = <1>;

		#size-cells = <1>;

		midi_in_out@0 {

			reg = <0 1>;

			protocol = "midi1-up-to-128b";

		};

	};

};

CONFIG_USB_DEVICE_STACK_NEXT=y

CONFIG_USBD_MIDI2_CLASS=y

CONFIG_SAMPLE_USBD_PRODUCT="USBD MIDI Sample"

CONFIG_SAMPLE_USBD_PID=0x0010

CONFIG_INPUT=y

CONFIG_LOG=y

CONFIG_USBD_LOG_LEVEL_WRN=y

CONFIG_UDC_DRIVER_LOG_LEVEL_WRN=y