boards: shields: olimex_shield_midi: new shield

Add a new very simple shield that provides MIDI DIN-5 IN/OUT/THROUGH,
as well as 2 leds. Other features of the shields (capacitive sensors)
are currently not reified in Zephyr.

While there is no further device on the shield itself (everything goes
through the Arduino header directly), this allows for meaningful
device-tree naming when using the shield.

Signed-off-by: Titouan Christophe <[email protected]>

Author: titouanc

boards/shields/olimex_shield_midi/Kconfig.shield

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+# Copyright (c) 2025 Titouan Christophe
+# SPDX-License-Identifier: Apache-2.0
+
+config SHIELD_OLIMEX_SHIELD_MIDI
+	def_bool $(shields_list_contains,olimex_shield_midi)

boards/shields/olimex_shield_midi/doc/index.rst

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+.. _olimex_shield_midi:
+
+Olimex SHIELD-MIDI
+##################
+
+Overview
+********
+
+This is a MIDI shield which allows Arduino like boards to receive and send MIDI
+messages. The shield allows direct wiring of up to 5 piezzo sensors and a
+keyboard (with buttons and serial resistors) making it ideal for drums projects.
+
+.. figure:: olimex_shield_midi.jpg
+   :align: center
+   :alt: Olimex SHIELD-MIDI
+
+* MIDI-IN, MIDI-OUT and MIDI-THRU connectors
+* 5 Piezzo sensors for drum implementation
+* Keyboard for piano implementation
+* Works with both 3.3V and 5V Arduino-like boards
+
+More information on the `SHIELD-MIDI website`_.
+
+Peripherals
+***********
+
+The following peripherals are available in Zephyr:
+
+- MIDI IN/OUT: on ``midi_serial`` (set at 31.25kb/s)
+- leds: ``midi_green_led``, ``midi_red_led``
+
+Programming
+***********
+
+Set ``--shield olimex_shield_midi`` when you invoke ``west build``. For example:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/net/midi2
+   :board: nucleo_f429zi
+   :shield: olimex_shield_midi
+   :goals: build
+
+.. _SHIELD-MIDI website:
+   https://www.olimex.com/Products/Duino/Shields/SHIELD-MIDI/open-source-hardware

boards/shields/olimex_shield_midi/doc/olimex_shield_midi.jpg

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+/*
+ * Copyright (c) 2025 Titouan Christophe
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	leds {
+		midi_green_led: midi-green-led {
+			gpios = <&arduino_header 13 GPIO_ACTIVE_HIGH>;
+		};
+
+		midi_red_led: midi-red-led {
+			gpios = <&arduino_header 12 GPIO_ACTIVE_HIGH>;
+		};
+	};
+};
+
+midi_serial: &arduino_serial {
+	current-speed = <31250>;
+};

boards/shields/olimex_shield_midi/olimex_shield_midi.overlay

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+shield:
+  name: olimex_shield_midi
+  full_name: Olimex SHIELD-MIDI
+  vendor: olimex
+  supported_features:
+    - led
+    - uart