Add multi thread Example

- Demonstrate that direct zephyr calls can be made even with the Arduino API in use.
- Examples shows concurrency by async blinking of 3 LEDs

Signed-off-by: Dhruva Gole <goledhruva@gmail.com>

Author: DhruvaG2000

samples/threads_arduino/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(threads)
+
+target_sources(app PRIVATE src/main.cpp)

samples/threads_arduino/README.rst

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+.. _arduino_nano_33_ble_multi_thread_blinky:
+
+Basic Thread Example
+####################
+
+Overview
+********
+
+This example demonstrates spawning multiple threads using
+:c:func:`K_THREAD_DEFINE`. It spawns three threads. Each thread is then defined
+at compile time using `K_THREAD_DEFINE`.
+
+These three each control an LED. These LEDs, ``LED_BUILTIN``, ``D10`` and ``D11``, have
+loop control and timing logic controlled by separate functions.
+
+- ``blink0()`` controls ``LED_BUILTIN`` and has a 100ms sleep cycle
+- ``blink1()`` controls ``D11`` and has a 1000ms sleep cycle
+- ``loop()`` controls ``D10`` and has a 300ms sleep cycle
+
+Requirements
+************
+
+The board must have two LEDs connected via GPIO pins and one builtin LED. These are called "User
+LEDs" on many of Zephyr's :ref:`boards`. The LEDs must be mapped using the `<board_name_pinmap.h>`
+``LED_BUILTIN``, ``D10`` and ``D11`` to the :ref:`devicetree <dt-guide>` aliases, in the
+variants folder.
+
+You will see one of these errors if you try to build this sample for an
+unsupported board:
+
+.. code-block:: none
+
+   Unsupported board: LED_BUILTIN devicetree alias is not defined
+   Unsupported board: D11 devicetree alias is not defined
+
+Building
+********
+
+For example, to build this sample for :ref:`arduino_nano_33_ble`:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/basic/arduino-threads
+   :board: arduino_nano_33_ble
+   :goals: build flash
+   :compact:
+
+Change ``arduino_nano_33_ble`` appropriately for other supported boards.

samples/threads_arduino/prj.conf

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+CONFIG_HEAP_MEM_POOL_SIZE=256
+CONFIG_GPIO=y
+CONFIG_CPLUSPLUS=y
+CONFIG_ARDUINO_API=y

samples/threads_arduino/src/main.cpp

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+/*
+ * Copyright (c) 2022 Dhruva Gole
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <Arduino.h>
+
+/* size of stack area used by each thread */
+#define STACKSIZE 1024
+
+/* scheduling priority used by each thread */
+#define PRIORITY 7
+
+void blink0(void)
+{
+	while (1) {
+		digitalWrite(LED_BUILTIN, HIGH);
+		delay(100);
+		digitalWrite(LED_BUILTIN, LOW);
+		delay(100);
+	}
+}
+
+void blink1(void)
+{
+	while (1) {
+		digitalWrite(D11, HIGH);
+		delay(1000);
+		digitalWrite(D11, LOW);
+		delay(1000);
+	}
+}
+
+K_THREAD_DEFINE(blink0_id, STACKSIZE, blink0, NULL, NULL, NULL, PRIORITY, 0, 0);
+K_THREAD_DEFINE(blink1_id, STACKSIZE, blink1, NULL, NULL, NULL, PRIORITY, 0, 0);
+K_THREAD_DEFINE(blink2_id, STACKSIZE, loop, NULL, NULL, NULL, PRIORITY, 0, 0);
+
+void setup()
+{
+	pinMode(LED_BUILTIN, OUTPUT);
+	pinMode(D11, OUTPUT);
+	pinMode(D10, OUTPUT);
+}
+void loop()
+{
+		digitalWrite(D10, HIGH);
+		delay(300);
+		digitalWrite(D10, LOW);
+		delay(300);
+}