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# `embedded-runtime-nrf52840`
This crate provides a tiny async runtime, targeted at embedded devices. Therefore, it provides a single-threaded
executor as well as a stack-allocated box to box futures. This crate injects a hardware implementation for the
`nrf52840`, based upon `wfe`/`sev`.

## Example
```rust
# use core::{
#     future::Future,
#     pin::Pin,
#     task::{Poll, Context}
# };
#
# /// Blocks until an event occurs (may wake spuriously)
# #[no_mangle]
# #[allow(non_snake_case)]
# pub fn _runtime_waitforevent_TBFzxdKN() {
#     // No-op
# }
# 
# /// Raises an event
# #[no_mangle]
# #[allow(non_snake_case)]
# pub fn _runtime_sendevent_3YSaPmB7() {
#     // No-op
# }
use embedded_runtime::run;

/// A countdown future that resolves to pending until the poll-countdown becomes zero
struct CountdownFuture {
    /// The current countdown value
    countdown: usize
}
impl CountdownFuture {
    /// Creates a new countdown future
    pub const fn new(countdown: usize) -> Self {
        Self { countdown }
    }
}
impl Future for CountdownFuture {
    type Output = ();

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
        // Decrement the value if we are still pending
        if self.countdown > 0 {
            // Print the countdown
            println!("{}!", self.countdown);

            // Decrement the future, wake the executor and return pending
            *self = Self::new(self.countdown - 1);
            cx.waker().wake_by_ref();
            return Poll::Pending;
        }

        // Return ready
        println!("Liftoff 🚀");
        Poll::Ready(())
    }
}

// This creates a new runtime and executes the given futures in an async context
run!(async {
    CountdownFuture::new(3).await;
    CountdownFuture::new(7).await;
}).expect("failed to perform countdowns");
```