feat: add an example demonstrating UDP echo over USB

This example is a direct port of the embassy-net TCP echo example, but
with UDP instead.

examples/embassy-net-udp/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "embassy-net-udp"
+version = "0.1.0"
+authors.workspace = true
+edition.workspace = true
+publish = false
+
+[dependencies]
+riot-rs = { path = "../../src/riot-rs", features = [ "time", "usb_ethernet"] }
+riot-rs-boards = { path = "../../src/riot-rs-boards" }
+embassy-executor = { workspace = true, default-features = false }
+embassy-time = { workspace = true, default-features = false }
+linkme.workspace = true
+embassy-net = { workspace = true, features = ["udp", "nightly"] }
+embedded-io-async = "0.6.0"

examples/embassy-net-udp/README.md

@@ -0,0 +1,15 @@
+# embassy-net-udp
+
+## About
+
+This application is testing basic
+[embassy](https://github.com/embassy-rs/embassy) _networking_ usage with RIOT-rs.
+
+## How to run
+
+In this folder, run
+
+    laze build -b nrf52840dk run
+
+With the device USB cable connected, a USB ethernet device should pop up.
+RIOT-rs will reply to ping requests on 10.0.42.61.

examples/embassy-net-udp/laze.yml

@@ -0,0 +1,4 @@
+apps:
+  - name: embassy-net-udp
+    selects:
+      - ?release

examples/embassy-net-udp/src/main.rs

@@ -0,0 +1,75 @@
+#![no_main]
+#![no_std]
+#![feature(type_alias_impl_trait)]
+#![feature(used_with_arg)]
+
+use riot_rs as _;
+
+use riot_rs::embassy::TaskArgs;
+use riot_rs::rt::debug::println;
+
+#[embassy_executor::task]
+async fn udp_echo(args: TaskArgs) {
+    use embassy_net::udp::{UdpSocket, PacketMetadata};
+    let stack = args.stack;
+
+    let mut rx_meta = [PacketMetadata::EMPTY; 16];
+    let mut rx_buffer = [0; 4096];
+    let mut tx_meta = [PacketMetadata::EMPTY; 16];
+    let mut tx_buffer = [0; 4096];
+    let mut buf = [0; 4096];
+
+    loop {
+        let mut socket = UdpSocket::new(stack, &mut rx_meta, &mut rx_buffer, &mut tx_meta, &mut tx_buffer);
+
+        println!("Listening on UDP:1234...");
+        if let Err(e) = socket.bind(1234) {
+            println!("bind error: {:?}", e);
+            continue;
+        }
+
+        loop {
+            let (n, remote_endpoint) = match socket.recv_from(&mut buf).await {
+                Ok((0, _)) => {
+                    println!("read EOF");
+                    break;
+                }
+                Ok((n, remote_endpoint)) => (n, remote_endpoint),
+                Err(e) => {
+                    println!("read error: {:?}", e);
+                    break;
+                }
+            };
+
+            println!("Received datagram from {:?}", remote_endpoint);
+
+            //println!("rxd {:02x}", &buf[..n]);
+
+            match socket.send_to(&buf[..n], remote_endpoint).await {
+                Ok(()) => {}
+                Err(e) => {
+                    println!("write error: {:?}", e);
+                    break;
+                }
+            };
+        }
+    }
+}
+
+use linkme::distributed_slice;
+use riot_rs::embassy::EMBASSY_TASKS;
+
+#[distributed_slice(EMBASSY_TASKS)]
+fn __start_udp_echo(spawner: embassy_executor::Spawner, t: TaskArgs) {
+    spawner.spawn(udp_echo(t)).unwrap();
+}
+
+#[no_mangle]
+fn riot_main() {
+    println!(
+        "Hello from riot_main()! Running on a {} board.",
+        riot_rs::buildinfo::BOARD
+    );
+
+    loop {}
+}

examples/laze.yml

@@ -9,6 +9,7 @@ subdirs:
   - core-sizes
   - embassy
   - embassy-net-tcp
+  - embassy-net-udp
     #  - embassy-gpio
   - hello-world
   - minimal