Function block_on 

pub fn block_on<F, W>(future: F, wait: W) -> F::Output
where
    F: Future + Unpin,
    W: FnMut(),

Run future to completion and return its output. This will repeatedly poll the future and call wait().

This is useful for microcontrollers that can be set into a low-power mode while waiting, such as using Cortex-M’s wfi instruction.

use futures::pin_mut;

let task = async { true };
pin_mut!(task);

let output = async_hal::block_on(task, || {
    dbg!("Waiting!");
});
assert!(output);