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samples: subsys: usb: midi: add new sample
Add a sample application that demonstrates how to use the new USB-MIDI 2.0 device class. This shows how to set up the device tree, how to exchange MIDI data with the host, and how to use the data accessors provided by the new API. Signed-off-by: Titouan Christophe <[email protected]>
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‎samples/subsys/usb/midi/CMakeLists.txt‎

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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(usb_midi)
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include(${ZEPHYR_BASE}/samples/subsys/usb/common/common.cmake)
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FILE(GLOB app_sources src/*.c)
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target_sources(app PRIVATE ${app_sources})

‎samples/subsys/usb/midi/Kconfig‎

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# Copyright (c) 2024 Titouan Christophe
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# SPDX-License-Identifier: Apache-2.0
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# Source common USB sample options used to initialize new experimental USB
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# device stack. The scope of these options is limited to USB samples in project
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# tree, you cannot use them in your own application.
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source "samples/subsys/usb/common/Kconfig.sample_usbd"
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source "Kconfig.zephyr"

‎samples/subsys/usb/midi/README.rst‎

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

‎samples/subsys/usb/midi/app.overlay‎

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/*
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* Copyright (c) 2024 Titouan Christophe
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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/ {
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usb_midi: usb_midi {
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compatible = "zephyr,midi2-device";
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status = "okay";
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#address-cells = <1>;
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#size-cells = <1>;
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midi_in_out@0 {
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reg = <0 1>;
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protocol = "midi1-up-to-128b";
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};
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};
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};

‎samples/subsys/usb/midi/prj.conf‎

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CONFIG_USB_DEVICE_STACK_NEXT=y
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CONFIG_USBD_MIDI2_CLASS=y
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CONFIG_SAMPLE_USBD_PRODUCT="USBD MIDI Sample"
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CONFIG_SAMPLE_USBD_PID=0x0010
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CONFIG_INPUT=y
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CONFIG_LOG=y
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CONFIG_USBD_LOG_LEVEL_WRN=y
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CONFIG_UDC_DRIVER_LOG_LEVEL_WRN=y

‎samples/subsys/usb/midi/sample.yaml‎

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sample:
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name: USB MIDI 2.0 device class sample
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tests:
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sample.usb_device_next.midi:
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depends_on: usbd
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tags: usb
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harness: console
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harness_config:
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type: one_line
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regex:
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- "USB device support enabled"

‎samples/subsys/usb/midi/src/main.c‎

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/*
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* Copyright (c) 2024 Titouan Christophe
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* @file
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* @brief Sample application for USB MIDI 2.0 device class
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*/
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#include <sample_usbd.h>
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#include <zephyr/device.h>
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#include <zephyr/drivers/gpio.h>
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#include <zephyr/input/input.h>
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#include <zephyr/usb/class/usbd_midi2.h>
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#include <zephyr/logging/log.h>
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LOG_MODULE_REGISTER(sample_usb_midi, LOG_LEVEL_INF);
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static const struct device *const midi = DEVICE_DT_GET(DT_NODELABEL(usb_midi));
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static struct gpio_dt_spec led = GPIO_DT_SPEC_GET_OR(DT_ALIAS(led0), gpios, {0});
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static void key_press(struct input_event *evt, void *user_data)
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{
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/* Only handle key presses in the 7bit MIDI range */
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if (evt->type != INPUT_EV_KEY || evt->code > 0x7f) {
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return;
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}
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uint8_t command = evt->value ? UMP_MIDI_NOTE_ON : UMP_MIDI_NOTE_OFF;
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uint8_t channel = 0;
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uint8_t note = evt->code;
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uint8_t velocity = 100;
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struct midi_ump ump = UMP_MIDI1_CHANNEL_VOICE(0, command, channel,
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note, velocity);
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usbd_midi_send(midi, ump);
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}
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INPUT_CALLBACK_DEFINE(NULL, key_press, NULL);
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static void on_midi_packet(const struct device *dev, const struct midi_ump ump)
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{
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LOG_INF("Received MIDI packet (MT=%X)", UMP_MT(ump));
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/* Only send MIDI1 channel voice messages back to the host */
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if (UMP_MT(ump) == UMP_MT_MIDI1_CHANNEL_VOICE) {
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LOG_INF("Send back MIDI1 message %02X %02X %02X", UMP_MIDI_STATUS(ump),
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UMP_MIDI1_P1(ump), UMP_MIDI1_P2(ump));
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usbd_midi_send(dev, ump);
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}
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}
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static void on_device_ready(const struct device *dev, const bool ready)
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{
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/* Light up the LED (if any) when USB-MIDI2.0 is enabled */
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if (led.port) {
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gpio_pin_set_dt(&led, ready);
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}
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}
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static const struct usbd_midi_ops ops = {
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.rx_packet_cb = on_midi_packet,
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.ready_cb = on_device_ready,
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};
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int main(void)
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{
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struct usbd_context *sample_usbd;
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if (!device_is_ready(midi)) {
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LOG_ERR("MIDI device not ready");
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return -1;
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}
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if (led.port) {
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if (gpio_pin_configure_dt(&led, GPIO_OUTPUT)) {
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LOG_ERR("Unable to setup LED, not using it");
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memset(&led, 0, sizeof(led));
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}
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}
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usbd_midi_set_ops(midi, &ops);
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sample_usbd = sample_usbd_init_device(NULL);
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if (sample_usbd == NULL) {
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LOG_ERR("Failed to initialize USB device");
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return -1;
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}
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if (usbd_enable(sample_usbd)) {
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LOG_ERR("Failed to enable device support");
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return -1;
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}
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LOG_INF("USB device support enabled");
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return 0;
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}

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