aioespnow: Add library providing asyncio support for espnow module.

This module provides asyncio support for the espnow module on ESP32 and
ESP8266 ports.

micropython/aioespnow/README.md

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+# `aioespnow`
+
+A supplementary module which extends the micropython `espnow` module to provide
+`asyncio` support.
+
+- Asyncio support is available on all ESP32 targets as well as those ESP8266
+boards which include the `uasyncio` module (ie. ESP8266 devices with at least
+2MB flash storage).
+
+## API reference
+
+- class `AIOESPNow()`: inherits all the methods of the `ESPNow` class and
+  extends the interface with the following async methods:
+
+  - `async AIOESPNow.arecv()`
+
+      Asyncio support for ESPNow.recv(). Note that this method does not take a
+      timeout value as argument.
+
+  - `async AIOESPNow.airecv()`
+
+      Asyncio support for ESPNow.irecv(). Use this method to reduce memory
+      fragmentation, as it will reuse common storage for each new message
+      received, whereas the `arecv()` method will allocate new memory for every
+      message received.
+
+  - `async AIOESPNow.asend(mac, msg, sync=True)`
+  - `async AIOESPNow.asend(msg)`
+
+      Asyncio support for ESPNow.send().
+
+  - `__aiter__()/async __anext__()`
+
+      AIOESPNow also supports reading incoming messages by asynchronous
+      iteration using `async for`, eg:
+
+    ```python
+      e = AIOESPNow()
+      e.active(True)
+      async def recv_till_halt(e):
+          async for mac, msg in e:
+              print(mac, msg)
+              if msg == b'halt':
+                  break
+      asyncio.run(recv_till_halt(e))
+    ```
+
+## Example Usage
+
+A small async server example::
+
+```python
+    import network
+    import aioespnow
+    import uasyncio as asyncio
+
+    # A WLAN interface must be active to send()/recv()
+    network.WLAN(network.STA_IF).active(True)
+
+    e = aioespnow.AIOESPNow()  # Returns AIOESPNow enhanced with async support
+    e.active(True)
+    peer = b'\xbb\xbb\xbb\xbb\xbb\xbb'
+    e.add_peer(peer)
+
+    # Send a periodic ping to a peer
+    async def heartbeat(e, peer, period=30):
+        while True:
+            if not await e.asend(peer, b'ping'):
+                print("Heartbeat: peer not responding:", peer)
+            else:
+                print("Heartbeat: ping", peer)
+            await asyncio.sleep(period)
+
+    # Echo any received messages back to the sender
+    async def echo_server(e):
+        async for mac, msg in e:
+            print("Echo:", msg)
+            try:
+                await e.asend(mac, msg)
+            except OSError as err:
+                if len(err.args) > 1 and err.args[1] == 'ESP_ERR_ESPNOW_NOT_FOUND':
+                    e.add_peer(mac)
+                    await e.asend(mac, msg)
+
+    async def main(e, peer, timeout, period):
+        asyncio.create_task(heartbeat(e, peer, period))
+        asyncio.create_task(echo_server(e))
+        await asyncio.sleep(timeout)
+
+    asyncio.run(main(e, peer, 120, 10))
+```

micropython/aioespnow/aioespnow.py

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+# aioespnow module for MicroPython on ESP32 and ESP8266
+# MIT license; Copyright (c) 2022 Glenn Moloney @glenn20
+
+import uasyncio as asyncio
+import espnow
+
+
+# Modelled on the uasyncio.Stream class (extmod/stream/stream.py)
+# NOTE: Relies on internal implementation of uasyncio.core (_io_queue)
+class AIOESPNow(espnow.ESPNow):
+    # Read one ESPNow message
+    async def arecv(self):
+        yield asyncio.core._io_queue.queue_read(self)
+        return self.recv(0)  # type: ignore
+
+    async def airecv(self):
+        yield asyncio.core._io_queue.queue_read(self)
+        return self.irecv(0)  # type: ignore
+
+    async def asend(self, mac, msg=None, sync=None):
+        if msg is None:
+            msg, mac = mac, None  # If msg is None: swap mac and msg
+        yield asyncio.core._io_queue.queue_write(self)
+        return self.send(mac, msg, sync)  # type: ignore
+
+    # "async for" support
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        return await self.airecv()

micropython/aioespnow/manifest.py

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+metadata(
+    description="Extends the micropython espnow module with methods to support asyncio.",
+    version="0.1",
+)
+
+module("aioespnow.py")