Add module-level documentation for embassy::time

embassy/src/time/mod.rs

@@ -1,3 +1,6 @@
+/// Time abstractions
+/// To use these abstractions, first call `set_clock` with an instance of an monotonic `Clock`.
+///
 mod duration;
 mod instant;
 mod traits;
@@ -14,10 +17,16 @@ pub const TICKS_PER_SECOND: u64 = 32768;
 
 static mut CLOCK: Option<&'static dyn Clock> = None;
 
+/// Sets the clock used for the timing abstractions
+///
+/// Safety: Sets a mutable global.
 pub unsafe fn set_clock(clock: &'static dyn Clock) {
     CLOCK = Some(clock);
 }
 
+/// Return the current timestamp in ticks.
+/// This is guaranteed to be monotonic, i.e. a call to now() will always return
+/// a greater or equal value than earler calls.
 pub(crate) fn now() -> u64 {
     unsafe { unwrap!(CLOCK, "No clock set").now() }
 }