11 files changed, 413 insertions, 83 deletions

diff --git a/.gitignore b/.gitignore
index 96ef6c0b9..25d18d5aa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 /target
 Cargo.lock
+third_party
diff --git a/Cargo.toml b/Cargo.toml
index 25e30eff1..abce83ec6 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,11 +6,16 @@ members = [
     "examples",
 ]
 
+exclude = [
+    "third_party"
+]
+
 [patch.crates-io]
 panic-probe = { git = "https://github.com/knurling-rs/probe-run", branch="main" }
 defmt-rtt = { git = "https://github.com/knurling-rs/defmt", branch="cursed-symbol-names-linkers-must-repent-for-their-sins" }
 defmt = { git = "https://github.com/knurling-rs/defmt", branch="cursed-symbol-names-linkers-must-repent-for-their-sins" }
 static-executor = { git = "https://github.com/Dirbaio/static-executor", branch="multi"}
+futures-intrusive = { git = "https://github.com/Dirbaio/futures-intrusive", branch="master"}
 
 [profile.dev]
 codegen-units = 1
diff --git a/embassy-nrf/src/rtc.rs b/embassy-nrf/src/rtc.rs
index 55869c6e5..ddb4fd367 100644
--- a/embassy-nrf/src/rtc.rs
+++ b/embassy-nrf/src/rtc.rs
@@ -1,8 +1,6 @@
 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;
@@ -86,22 +84,25 @@ impl<T: Instance> RTC<T> {
         interrupt::enable(T::INTERRUPT);
     }
 
+    pub fn now(&self) -> u64 {
+        let counter = self.rtc.counter.read().bits();
+        let period = self.period.load(Ordering::Relaxed);
+        calc_now(period, counter)
+    }
+
     fn on_interrupt(&self) {
         if self.rtc.events_ovrflw.read().bits() == 1 {
             self.rtc.events_ovrflw.write(|w| w);
-            trace!("rtc overflow");
             self.next_period();
         }
 
         if self.rtc.events_compare[0].read().bits() == 1 {
             self.rtc.events_compare[0].write(|w| w);
-            trace!("rtc compare0");
             self.next_period();
         }
 
         if self.rtc.events_compare[1].read().bits() == 1 {
             self.rtc.events_compare[1].write(|w| w);
-            trace!("rtc compare1");
             self.trigger_alarm();
         }
     }
@@ -162,26 +163,28 @@ 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 alarm0(&'static self) -> Alarm<T> {
+        Alarm { rtc: self }
     }
+}
+
+pub struct Alarm<T: Instance> {
+    rtc: &'static RTC<T>,
+}
 
-    fn set_alarm(&self, timestamp: u64, callback: fn()) {
-        self.do_set_alarm(timestamp, Some(callback));
+impl<T: Instance> embassy::time::Alarm for Alarm<T> {
+    fn set(&self, timestamp: u64, callback: fn()) {
+        self.rtc.do_set_alarm(timestamp, Some(callback));
     }
 
-    fn clear_alarm(&self) {
-        self.do_set_alarm(u64::MAX, None);
+    fn clear(&self) {
+        self.rtc.do_set_alarm(u64::MAX, None);
     }
 }
 
 /// Implemented by all RTC instances.
-pub trait Instance: Deref<Target = rtc0::RegisterBlock> + Sized {
+pub trait Instance: Deref<Target = rtc0::RegisterBlock> + Sized + 'static {
     /// The interrupt associated with this RTC instance.
     const INTERRUPT: Interrupt;
 
diff --git a/embassy/Cargo.toml b/embassy/Cargo.toml
index 5826e8ba6..60428f10d 100644
--- a/embassy/Cargo.toml
+++ b/embassy/Cargo.toml
@@ -13,3 +13,4 @@ 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 }
+static-executor  = { version = "0.1.0", features=["defmt"]}
diff --git a/embassy/src/clock.rs b/embassy/src/clock.rs
deleted file mode 100644
index ca5f26a05..000000000
--- a/embassy/src/clock.rs
+++ /dev/null
@@ -1,21 +0,0 @@
-/// 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/executor.rs b/embassy/src/executor.rs
new file mode 100644
index 000000000..c5d024f7b
--- /dev/null
+++ b/embassy/src/executor.rs
@@ -0,0 +1,72 @@
+use core::marker::PhantomData;
+use static_executor as se;
+
+use crate::time;
+use crate::time::Alarm;
+
+pub use se::{task, SpawnError, SpawnToken};
+
+pub trait Model {
+    fn signal();
+}
+
+pub struct WfeModel;
+
+impl Model for WfeModel {
+    fn signal() {
+        cortex_m::asm::sev()
+    }
+}
+
+pub struct Executor<M, A: Alarm> {
+    inner: se::Executor,
+    alarm: A,
+    timer: time::TimerService,
+    _phantom: PhantomData<M>,
+}
+
+impl<M: Model, A: Alarm> Executor<M, A> {
+    pub fn new(alarm: A) -> Self {
+        Self {
+            inner: se::Executor::new(M::signal),
+            alarm,
+            timer: time::TimerService::new(time::IntrusiveClock),
+            _phantom: PhantomData,
+        }
+    }
+
+    /// Spawn a future on this executor.
+    ///
+    /// safety: can only be called from the executor thread
+    pub unsafe fn spawn(&'static self, token: SpawnToken) -> Result<(), SpawnError> {
+        self.inner.spawn(token)
+    }
+
+    /// Runs the executor until the queue is empty.
+    ///
+    /// safety: can only be called from the executor thread
+    pub unsafe fn run_once(&'static self) {
+        time::with_timer_service(&self.timer, || {
+            self.timer.check_expirations();
+            self.inner.run();
+
+            match self.timer.next_expiration() {
+                // If this is in the past, set_alarm will immediately trigger the alarm,
+                // which will make the wfe immediately return so we do another loop iteration.
+                Some(at) => self.alarm.set(at, M::signal),
+                None => self.alarm.clear(),
+            }
+        })
+    }
+}
+
+impl<A: Alarm> Executor<WfeModel, A> {
+    /// Runs the executor forever
+    /// safety: can only be called from the executor thread
+    pub unsafe fn run(&'static self) -> ! {
+        loop {
+            self.run_once();
+            cortex_m::asm::wfe()
+        }
+    }
+}
diff --git a/embassy/src/lib.rs b/embassy/src/lib.rs
index 89eef3f4c..92ad77424 100644
--- a/embassy/src/lib.rs
+++ b/embassy/src/lib.rs
@@ -3,7 +3,8 @@
 #![feature(generic_associated_types)]
 #![feature(const_fn)]
 
-pub mod clock;
+pub mod executor;
 pub mod flash;
 pub mod io;
+pub mod time;
 pub mod util;
diff --git a/embassy/src/time.rs b/embassy/src/time.rs
new file mode 100644
index 000000000..30fd1b680
--- /dev/null
+++ b/embassy/src/time.rs
@@ -0,0 +1,287 @@
+use core::cell::Cell;
+use core::convert::TryInto;
+use core::future::Future;
+use core::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};
+use core::pin::Pin;
+use core::ptr;
+use core::sync::atomic::{AtomicPtr, Ordering};
+use core::task::{Context, Poll};
+
+use fi::LocalTimer;
+use futures_intrusive::timer as fi;
+
+static mut CLOCK: fn() -> u64 = clock_not_set;
+
+fn clock_not_set() -> u64 {
+    panic!("No clock set. You must call embassy::time::set_clock() before trying to use the clock")
+}
+
+pub unsafe fn set_clock(clock: fn() -> u64) {
+    CLOCK = clock;
+}
+
+fn now() -> u64 {
+    unsafe { CLOCK() }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Instant {
+    ticks: u64,
+}
+
+impl Instant {
+    pub fn now() -> Instant {
+        Instant { ticks: now() }
+    }
+
+    pub fn into_ticks(&self) -> u64 {
+        self.ticks
+    }
+
+    pub fn duration_since(&self, earlier: Instant) -> Duration {
+        Duration {
+            ticks: (self.ticks - earlier.ticks).try_into().unwrap(),
+        }
+    }
+
+    pub fn checked_duration_since(&self, earlier: Instant) -> Option<Duration> {
+        if self.ticks < earlier.ticks {
+            None
+        } else {
+            Some(Duration {
+                ticks: (self.ticks - earlier.ticks).try_into().unwrap(),
+            })
+        }
+    }
+
+    pub fn saturating_duration_since(&self, earlier: Instant) -> Duration {
+        Duration {
+            ticks: if self.ticks < earlier.ticks {
+                0
+            } else {
+                (self.ticks - earlier.ticks).try_into().unwrap()
+            },
+        }
+    }
+
+    pub fn elapsed(&self) -> Duration {
+        Instant::now() - *self
+    }
+
+    pub fn checked_add(&self, duration: Duration) -> Option<Instant> {
+        self.ticks
+            .checked_add(duration.ticks.into())
+            .map(|ticks| Instant { ticks })
+    }
+    pub fn checked_sub(&self, duration: Duration) -> Option<Instant> {
+        self.ticks
+            .checked_sub(duration.ticks.into())
+            .map(|ticks| Instant { ticks })
+    }
+}
+
+impl Add<Duration> for Instant {
+    type Output = Instant;
+
+    fn add(self, other: Duration) -> Instant {
+        self.checked_add(other)
+            .expect("overflow when adding duration to instant")
+    }
+}
+
+impl AddAssign<Duration> for Instant {
+    fn add_assign(&mut self, other: Duration) {
+        *self = *self + other;
+    }
+}
+
+impl Sub<Duration> for Instant {
+    type Output = Instant;
+
+    fn sub(self, other: Duration) -> Instant {
+        self.checked_sub(other)
+            .expect("overflow when subtracting duration from instant")
+    }
+}
+
+impl SubAssign<Duration> for Instant {
+    fn sub_assign(&mut self, other: Duration) {
+        *self = *self - other;
+    }
+}
+
+impl Sub<Instant> for Instant {
+    type Output = Duration;
+
+    fn sub(self, other: Instant) -> Duration {
+        self.duration_since(other)
+    }
+}
+
+#[derive(Debug, Default, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Duration {
+    ticks: u32,
+}
+
+impl Duration {
+    pub const fn from_ticks(ticks: u32) -> Duration {
+        Duration { ticks }
+    }
+
+    pub fn checked_add(self, rhs: Duration) -> Option<Duration> {
+        self.ticks
+            .checked_add(rhs.ticks)
+            .map(|ticks| Duration { ticks })
+    }
+
+    pub fn checked_sub(self, rhs: Duration) -> Option<Duration> {
+        self.ticks
+            .checked_sub(rhs.ticks)
+            .map(|ticks| Duration { ticks })
+    }
+
+    pub fn checked_mul(self, rhs: u32) -> Option<Duration> {
+        self.ticks.checked_mul(rhs).map(|ticks| Duration { ticks })
+    }
+
+    pub fn checked_div(self, rhs: u32) -> Option<Duration> {
+        self.ticks.checked_div(rhs).map(|ticks| Duration { ticks })
+    }
+}
+
+impl Add for Duration {
+    type Output = Duration;
+
+    fn add(self, rhs: Duration) -> Duration {
+        self.checked_add(rhs)
+            .expect("overflow when adding durations")
+    }
+}
+
+impl AddAssign for Duration {
+    fn add_assign(&mut self, rhs: Duration) {
+        *self = *self + rhs;
+    }
+}
+
+impl Sub for Duration {
+    type Output = Duration;
+
+    fn sub(self, rhs: Duration) -> Duration {
+        self.checked_sub(rhs)
+            .expect("overflow when subtracting durations")
+    }
+}
+
+impl SubAssign for Duration {
+    fn sub_assign(&mut self, rhs: Duration) {
+        *self = *self - rhs;
+    }
+}
+
+impl Mul<u32> for Duration {
+    type Output = Duration;
+
+    fn mul(self, rhs: u32) -> Duration {
+        self.checked_mul(rhs)
+            .expect("overflow when multiplying duration by scalar")
+    }
+}
+
+impl Mul<Duration> for u32 {
+    type Output = Duration;
+
+    fn mul(self, rhs: Duration) -> Duration {
+        rhs * self
+    }
+}
+
+impl MulAssign<u32> for Duration {
+    fn mul_assign(&mut self, rhs: u32) {
+        *self = *self * rhs;
+    }
+}
+
+impl Div<u32> for Duration {
+    type Output = Duration;
+
+    fn div(self, rhs: u32) -> Duration {
+        self.checked_div(rhs)
+            .expect("divide by zero error when dividing duration by scalar")
+    }
+}
+
+impl DivAssign<u32> for Duration {
+    fn div_assign(&mut self, rhs: u32) {
+        *self = *self / rhs;
+    }
+}
+
+pub(crate) struct IntrusiveClock;
+
+impl fi::Clock for IntrusiveClock {
+    fn now(&self) -> u64 {
+        now()
+    }
+}
+
+pub(crate) type TimerService = fi::LocalTimerService<IntrusiveClock>;
+
+static CURRENT_TIMER_SERVICE: AtomicPtr<TimerService> = AtomicPtr::new(ptr::null_mut());
+
+pub(crate) fn with_timer_service<R>(svc: &'static TimerService, f: impl FnOnce() -> R) -> R {
+    let svc = svc as *const _ as *mut _;
+    let prev_svc = CURRENT_TIMER_SERVICE.swap(svc, Ordering::Relaxed);
+    let r = f();
+    let svc2 = CURRENT_TIMER_SERVICE.swap(prev_svc, Ordering::Relaxed);
+    assert_eq!(svc, svc2);
+    r
+}
+
+fn current_timer_service() -> &'static TimerService {
+    unsafe {
+        CURRENT_TIMER_SERVICE
+            .load(Ordering::Relaxed)
+            .as_ref()
+            .unwrap()
+    }
+}
+
+pub struct Timer {
+    inner: fi::LocalTimerFuture<'static>,
+}
+
+impl Timer {
+    pub fn at(when: Instant) -> Self {
+        let svc: &TimerService = current_timer_service();
+        Self {
+            inner: svc.deadline(when.into_ticks()),
+        }
+    }
+
+    pub fn after(dur: Duration) -> Self {
+        Self::at(Instant::now() + dur)
+    }
+}
+
+impl Future for Timer {
+    type Output = ();
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        unsafe { Pin::new_unchecked(&mut self.get_unchecked_mut().inner) }.poll(cx)
+    }
+}
+
+/// Trait to register a callback at a given timestamp.
+pub trait Alarm {
+    /// 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(&self, timestamp: u64, callback: fn());
+
+    /// Clears the previously-set alarm.
+    /// If no alarm was set, this is a noop.
+    fn clear(&self);
+}
diff --git a/examples/Cargo.toml b/examples/Cargo.toml
index 4e81d1daa..7b49ffb1f 100644
--- a/examples/Cargo.toml
+++ b/examples/Cargo.toml
@@ -27,5 +27,4 @@ nrf52840-hal    = { version = "0.11.0" }
 embassy = { version = "0.1.0", path = "../embassy" }
 embassy-nrf = { version = "0.1.0", path = "../embassy-nrf", features = ["defmt-trace", "52840"] }
 static-executor  = { version = "0.1.0", features=["defmt"]}
-futures = { version = "0.3.5", default-features = false }
-futures-intrusive = { version = "0.3.1", default-features = false }
\ No newline at end of file
+futures = { version = "0.3.5", default-features = false }
\ No newline at end of file
diff --git a/examples/src/bin/rtc_async.rs b/examples/src/bin/rtc_async.rs
index 977621d4c..3bffabf0f 100644
--- a/examples/src/bin/rtc_async.rs
+++ b/examples/src/bin/rtc_async.rs
@@ -8,39 +8,30 @@ use example_common::*;
 
 use core::mem::MaybeUninit;
 use cortex_m_rt::entry;
-use embassy::clock::Monotonic;
+use embassy::executor::{task, Executor, WfeModel};
+use embassy::time::{Duration, Instant, Timer};
+use embassy_nrf::pac;
 use embassy_nrf::rtc;
-use futures_intrusive::timer::{Clock, LocalTimer, LocalTimerService};
 use nrf52840_hal::clocks;
-use static_executor::{task, Executor};
-
-struct RtcClock<T>(rtc::RTC<T>);
-
-impl<T: rtc::Instance> Clock for RtcClock<T> {
-    fn now(&self) -> u64 {
-        self.0.now()
-    }
-}
 
 #[task]
-async fn run1(rtc: &'static rtc::RTC<embassy_nrf::pac::RTC1>, timer: &'static LocalTimerService) {
+async fn run1() {
     loop {
-        info!("tick 1");
-        timer.deadline(rtc.now() + 64000).await;
+        info!("BIG INFREQUENT TICK");
+        Timer::after(Duration::from_ticks(64000)).await;
     }
 }
 
 #[task]
-async fn run2(rtc: &'static rtc::RTC<embassy_nrf::pac::RTC1>, timer: &'static LocalTimerService) {
+async fn run2() {
     loop {
-        info!("tick 2");
-        timer.deadline(rtc.now() + 23000).await;
+        info!("tick");
+        Timer::after(Duration::from_ticks(13000)).await;
     }
 }
 
-static EXECUTOR: Executor = Executor::new(cortex_m::asm::sev);
-static mut RTC: MaybeUninit<RtcClock<embassy_nrf::pac::RTC1>> = MaybeUninit::uninit();
-static mut TIMER: MaybeUninit<LocalTimerService> = MaybeUninit::uninit();
+static mut RTC: MaybeUninit<rtc::RTC<pac::RTC1>> = MaybeUninit::uninit();
+static mut EXECUTOR: MaybeUninit<Executor<WfeModel, rtc::Alarm<pac::RTC1>>> = MaybeUninit::uninit();
 
 #[entry]
 fn main() -> ! {
@@ -55,35 +46,23 @@ fn main() -> ! {
 
     let rtc: &'static _ = unsafe {
         let ptr = RTC.as_mut_ptr();
-        ptr.write(RtcClock(rtc::RTC::new(p.RTC1)));
+        ptr.write(rtc::RTC::new(p.RTC1));
         &*ptr
     };
 
-    rtc.0.start();
+    rtc.start();
+    unsafe { embassy::time::set_clock(|| RTC.as_ptr().as_ref().unwrap().now()) };
 
-    let timer: &'static _ = unsafe {
-        let ptr = TIMER.as_mut_ptr();
-        ptr.write(LocalTimerService::new(rtc));
+    let executor: &'static _ = unsafe {
+        let ptr = EXECUTOR.as_mut_ptr();
+        ptr.write(Executor::new(rtc.alarm0()));
         &*ptr
     };
 
     unsafe {
-        EXECUTOR.spawn(run1(&rtc.0, timer)).dewrap();
-        EXECUTOR.spawn(run2(&rtc.0, timer)).dewrap();
-
-        loop {
-            timer.check_expirations();
-
-            EXECUTOR.run();
-
-            match timer.next_expiration() {
-                // If this is in the past, set_alarm will immediately trigger the alarm,
-                // which will make the wfe immediately return so we do another loop iteration.
-                Some(at) => rtc.0.set_alarm(at, cortex_m::asm::sev),
-                None => rtc.0.clear_alarm(),
-            }
+        executor.spawn(run1()).dewrap();
+        executor.spawn(run2()).dewrap();
 
-            cortex_m::asm::wfe();
-        }
+        executor.run()
     }
 }
diff --git a/examples/src/bin/rtc_raw.rs b/examples/src/bin/rtc_raw.rs
index aa98409c4..2e4b28653 100644
--- a/examples/src/bin/rtc_raw.rs
+++ b/examples/src/bin/rtc_raw.rs
@@ -8,7 +8,7 @@ use example_common::*;
 
 use core::mem::MaybeUninit;
 use cortex_m_rt::entry;
-use embassy::clock::Monotonic;
+use embassy::time::Alarm;
 use embassy_nrf::rtc;
 use nrf52840_hal::clocks;
 
@@ -31,8 +31,11 @@ fn main() -> ! {
         &*ptr
     };
 
+    let alarm = rtc.alarm0();
+
     rtc.start();
-    rtc.set_alarm(53719, || info!("ALARM TRIGGERED"));
+
+    alarm.set(53719, || info!("ALARM TRIGGERED"));
 
     info!("initialized!");