6 files changed, 44 insertions, 17 deletions

diff --git a/embassy-nrf/src/rtc.rs b/embassy-nrf/src/rtc.rs
index 95ee1a068..55869c6e5 100644
--- a/embassy-nrf/src/rtc.rs
+++ b/embassy-nrf/src/rtc.rs
@@ -1,8 +1,8 @@
 use core::cell::Cell;
 use core::ops::Deref;
 use core::sync::atomic::{AtomicU32, Ordering};
-
 use defmt::trace;
+use embassy::clock::Monotonic;
 
 use crate::interrupt;
 use crate::interrupt::Mutex;
@@ -121,12 +121,6 @@ impl<T: Instance> RTC<T> {
         })
     }
 
-    pub fn now(&self) -> u64 {
-        let counter = self.rtc.counter.read().bits();
-        let period = self.period.load(Ordering::Relaxed);
-        calc_now(period, counter)
-    }
-
     fn trigger_alarm(&self) {
         self.rtc.intenclr.write(|w| w.compare1().clear());
         interrupt::free(|cs| {
@@ -139,19 +133,19 @@ impl<T: Instance> RTC<T> {
         });
     }
 
-    fn do_set_alarm(&self, at: u64, f: Option<fn()>) {
+    fn do_set_alarm(&self, timestamp: u64, callback: Option<fn()>) {
         interrupt::free(|cs| {
-            self.alarm.borrow(cs).set((at, f));
+            self.alarm.borrow(cs).set((timestamp, callback));
 
             let t = self.now();
-            if at <= t {
+            if timestamp <= t {
                 self.trigger_alarm();
                 return;
             }
 
-            let diff = at - t;
+            let diff = timestamp - t;
             if diff < 0xc00000 {
-                self.rtc.cc[1].write(|w| unsafe { w.bits(at as u32 & 0xFFFFFF) });
+                self.rtc.cc[1].write(|w| unsafe { w.bits(timestamp as u32 & 0xFFFFFF) });
                 self.rtc.intenset.write(|w| w.compare1().set());
 
                 // We may have been preempted for arbitrary time between checking if `at` is in the past
@@ -159,7 +153,7 @@ impl<T: Instance> RTC<T> {
                 // So, we check again just in case.
 
                 let t = self.now();
-                if at <= t {
+                if timestamp <= t {
                     self.trigger_alarm();
                     return;
                 }
@@ -168,12 +162,20 @@ impl<T: Instance> RTC<T> {
             }
         })
     }
+}
+
+impl<T: Instance> Monotonic for RTC<T> {
+    fn now(&self) -> u64 {
+        let counter = self.rtc.counter.read().bits();
+        let period = self.period.load(Ordering::Relaxed);
+        calc_now(period, counter)
+    }
 
-    pub fn set_alarm(&self, at: u64, f: fn()) {
-        self.do_set_alarm(at, Some(f));
+    fn set_alarm(&self, timestamp: u64, callback: fn()) {
+        self.do_set_alarm(timestamp, Some(callback));
     }
 
-    pub fn clear_alarm(&self) {
+    fn clear_alarm(&self) {
         self.do_set_alarm(u64::MAX, None);
     }
 }
diff --git a/embassy/Cargo.toml b/embassy/Cargo.toml
index f621015ab..5826e8ba6 100644
--- a/embassy/Cargo.toml
+++ b/embassy/Cargo.toml
@@ -12,3 +12,4 @@ defmt = "0.1.0"
 cortex-m = "0.6.3"
 futures     = { version = "0.3.5", default-features = false, features = [ "async-await" ] }
 pin-project = { version = "0.4.23", default-features = false }
+futures-intrusive = { version = "0.3.1", default-features = false }
diff --git a/embassy/src/clock.rs b/embassy/src/clock.rs
new file mode 100644
index 000000000..ca5f26a05
--- /dev/null
+++ b/embassy/src/clock.rs
@@ -0,0 +1,21 @@
+/// Monotonic clock with support for setting an alarm.
+///
+/// The clock uses a "tick" time unit, whose length is an implementation-dependent constant.
+pub trait Monotonic {
+    /// Returns 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.
+    fn now(&self) -> u64;
+
+    /// Sets an alarm at the given timestamp. When the clock reaches that
+    /// timestamp, the provided callback funcion will be called.
+    ///
+    /// When callback is called, it is guaranteed that now() will return a value greater or equal than timestamp.
+    ///
+    /// Only one alarm can be active at a time. This overwrites any previously-set alarm if any.
+    fn set_alarm(&self, timestamp: u64, callback: fn());
+
+    /// Clears the previously-set alarm.
+    /// If no alarm was set, this is a noop.
+    fn clear_alarm(&self);
+}
diff --git a/embassy/src/lib.rs b/embassy/src/lib.rs
index 45716c6cf..89eef3f4c 100644
--- a/embassy/src/lib.rs
+++ b/embassy/src/lib.rs
@@ -3,6 +3,7 @@
 #![feature(generic_associated_types)]
 #![feature(const_fn)]
 
+pub mod clock;
 pub mod flash;
-pub mod util;
 pub mod io;
+pub mod util;
diff --git a/examples/src/bin/rtc_async.rs b/examples/src/bin/rtc_async.rs
index 838a0faef..977621d4c 100644
--- a/examples/src/bin/rtc_async.rs
+++ b/examples/src/bin/rtc_async.rs
@@ -8,6 +8,7 @@ use example_common::*;
 
 use core::mem::MaybeUninit;
 use cortex_m_rt::entry;
+use embassy::clock::Monotonic;
 use embassy_nrf::rtc;
 use futures_intrusive::timer::{Clock, LocalTimer, LocalTimerService};
 use nrf52840_hal::clocks;
diff --git a/examples/src/bin/rtc_raw.rs b/examples/src/bin/rtc_raw.rs
index 8debf12e3..aa98409c4 100644
--- a/examples/src/bin/rtc_raw.rs
+++ b/examples/src/bin/rtc_raw.rs
@@ -8,6 +8,7 @@ use example_common::*;
 
 use core::mem::MaybeUninit;
 use cortex_m_rt::entry;
+use embassy::clock::Monotonic;
 use embassy_nrf::rtc;
 use nrf52840_hal::clocks;