traits: add delay trait

delay allows downstream libraries
to use async delay without depending
on a specific delay implementation

embassy-traits/src/delay.rs

@@ -0,0 +1,9 @@
+use core::future::Future;
+use core::pin::Pin;
+
+pub trait Delay {
+    type DelayFuture<'a>: Future<Output = ()> + 'a;
+
+    fn delay_ms<'a>(self: Pin<&'a mut Self>, millis: u64) -> Self::DelayFuture<'a>;
+    fn delay_us<'a>(self: Pin<&'a mut Self>, micros: u64) -> Self::DelayFuture<'a>;
+}

embassy-traits/src/lib.rs

@@ -5,6 +5,7 @@
 #![feature(const_option)]
 #![allow(incomplete_features)]
 
+pub mod delay;
 pub mod flash;
 pub mod gpio;
 pub mod uart;