nrf: add manually_create_executor example.

examples/nrf/src/bin/manually_create_executor.rs

@@ -0,0 +1,49 @@
+// This example showcases how to manually create an executor.
+// This is what the #[embassy::main] macro does behind the scenes.
+
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use cortex_m_rt::entry;
+use defmt::{info, unwrap};
+use embassy_executor::Executor;
+use embassy_time::{Duration, Timer};
+use static_cell::StaticCell;
+use {defmt_rtt as _, panic_probe as _};
+
+#[embassy_executor::task]
+async fn run1() {
+    loop {
+        info!("BIG INFREQUENT TICK");
+        Timer::after(Duration::from_ticks(64000)).await;
+    }
+}
+
+#[embassy_executor::task]
+async fn run2() {
+    loop {
+        info!("tick");
+        Timer::after(Duration::from_ticks(13000)).await;
+    }
+}
+
+static EXECUTOR: StaticCell<Executor> = StaticCell::new();
+
+#[entry]
+fn main() -> ! {
+    info!("Hello World!");
+
+    let _p = embassy_nrf::init(Default::default());
+
+    // Create the executor and put it in a StaticCell, because `run` needs `&'static mut Executor`.
+    let executor = EXECUTOR.init(Executor::new());
+
+    // Run it.
+    // `run` calls the closure then runs the executor forever. It never returns.
+    executor.run(|spawner| {
+        // Here we get access to a spawner to spawn the initial tasks.
+        unwrap!(spawner.spawn(run1()));
+        unwrap!(spawner.spawn(run2()));
+    });
+}