Merge pull request #3593 from bugadani/refactor

Rework time-driver contract.

12 files changed, 176 insertions, 237 deletions

diff --git a/embassy-executor/src/arch/avr.rs b/embassy-executor/src/arch/avr.rs
index 7f9ed4421..70085d04d 100644
--- a/embassy-executor/src/arch/avr.rs
+++ b/embassy-executor/src/arch/avr.rs
@@ -53,10 +53,6 @@ mod thread {
         ///
         /// This function never returns.
         pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
-            unsafe {
-                self.inner.initialize();
-            }
-
             init(self.inner.spawner());
 
             loop {
diff --git a/embassy-executor/src/arch/cortex_m.rs b/embassy-executor/src/arch/cortex_m.rs
index 0c2af88a6..5c517e0a2 100644
--- a/embassy-executor/src/arch/cortex_m.rs
+++ b/embassy-executor/src/arch/cortex_m.rs
@@ -98,9 +98,6 @@ mod thread {
         ///
         /// This function never returns.
         pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
-            unsafe {
-                self.inner.initialize();
-            }
             init(self.inner.spawner());
 
             loop {
@@ -210,9 +207,6 @@ mod interrupt {
             }
 
             let executor = unsafe { (&*self.executor.get()).assume_init_ref() };
-            unsafe {
-                executor.initialize();
-            }
 
             unsafe { NVIC::unmask(irq) }
 
diff --git a/embassy-executor/src/arch/riscv32.rs b/embassy-executor/src/arch/riscv32.rs
index 715e5f3cf..01e63a9fd 100644
--- a/embassy-executor/src/arch/riscv32.rs
+++ b/embassy-executor/src/arch/riscv32.rs
@@ -54,10 +54,6 @@ mod thread {
         ///
         /// This function never returns.
         pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
-            unsafe {
-                self.inner.initialize();
-            }
-
             init(self.inner.spawner());
 
             loop {
diff --git a/embassy-executor/src/arch/spin.rs b/embassy-executor/src/arch/spin.rs
index 54c7458b3..340023620 100644
--- a/embassy-executor/src/arch/spin.rs
+++ b/embassy-executor/src/arch/spin.rs
@@ -48,10 +48,6 @@ mod thread {
         ///
         /// This function never returns.
         pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
-            unsafe {
-                self.inner.initialize();
-            }
-
             init(self.inner.spawner());
 
             loop {
diff --git a/embassy-executor/src/arch/std.rs b/embassy-executor/src/arch/std.rs
index 948c7711b..b02b15988 100644
--- a/embassy-executor/src/arch/std.rs
+++ b/embassy-executor/src/arch/std.rs
@@ -55,10 +55,6 @@ mod thread {
         ///
         /// This function never returns.
         pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
-            unsafe {
-                self.inner.initialize();
-            }
-
             init(self.inner.spawner());
 
             loop {
diff --git a/embassy-executor/src/arch/wasm.rs b/embassy-executor/src/arch/wasm.rs
index 35025f11f..f9d0f935c 100644
--- a/embassy-executor/src/arch/wasm.rs
+++ b/embassy-executor/src/arch/wasm.rs
@@ -71,10 +71,6 @@ mod thread {
         /// - a local variable in a function you know never returns (like `fn main() -> !`), upgrading its lifetime with `transmute`. (unsafe)
         pub fn start(&'static mut self, init: impl FnOnce(Spawner)) {
             unsafe {
-                self.inner.initialize();
-            }
-
-            unsafe {
                 let executor = &self.inner;
                 let future = Closure::new(move |_| {
                     executor.poll();
diff --git a/embassy-executor/src/raw/mod.rs b/embassy-executor/src/raw/mod.rs
index 3f93eae6f..7da14468d 100644
--- a/embassy-executor/src/raw/mod.rs
+++ b/embassy-executor/src/raw/mod.rs
@@ -16,8 +16,7 @@ mod run_queue;
 #[cfg_attr(not(target_has_atomic = "8"), path = "state_critical_section.rs")]
 mod state;
 
-#[cfg(feature = "integrated-timers")]
-mod timer_queue;
+pub mod timer_queue;
 #[cfg(feature = "trace")]
 mod trace;
 pub(crate) mod util;
@@ -31,9 +30,6 @@ use core::pin::Pin;
 use core::ptr::NonNull;
 use core::task::{Context, Poll};
 
-#[cfg(feature = "integrated-timers")]
-use embassy_time_driver::AlarmHandle;
-
 use self::run_queue::{RunQueue, RunQueueItem};
 use self::state::State;
 use self::util::{SyncUnsafeCell, UninitCell};
@@ -47,14 +43,12 @@ pub(crate) struct TaskHeader {
     pub(crate) executor: SyncUnsafeCell<Option<&'static SyncExecutor>>,
     poll_fn: SyncUnsafeCell<Option<unsafe fn(TaskRef)>>,
 
-    #[cfg(feature = "integrated-timers")]
-    pub(crate) expires_at: SyncUnsafeCell<u64>,
-    #[cfg(feature = "integrated-timers")]
+    /// Integrated timer queue storage. This field should not be accessed outside of the timer queue.
     pub(crate) timer_queue_item: timer_queue::TimerQueueItem,
 }
 
 /// This is essentially a `&'static TaskStorage<F>` where the type of the future has been erased.
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, PartialEq)]
 pub struct TaskRef {
     ptr: NonNull<TaskHeader>,
 }
@@ -76,10 +70,53 @@ impl TaskRef {
         }
     }
 
+    /// # Safety
+    ///
+    /// The result of this function must only be compared
+    /// for equality, or stored, but not used.
+    pub const unsafe fn dangling() -> Self {
+        Self {
+            ptr: NonNull::dangling(),
+        }
+    }
+
     pub(crate) fn header(self) -> &'static TaskHeader {
         unsafe { self.ptr.as_ref() }
     }
 
+    /// Returns a reference to the executor that the task is currently running on.
+    pub unsafe fn executor(self) -> Option<&'static Executor> {
+        self.header().executor.get().map(|e| Executor::wrap(e))
+    }
+
+    /// Returns a reference to the timer queue item.
+    pub fn timer_queue_item(&self) -> &'static timer_queue::TimerQueueItem {
+        &self.header().timer_queue_item
+    }
+
+    /// Mark the task as timer-queued. Return whether it should be actually enqueued
+    /// using `_embassy_time_schedule_wake`.
+    ///
+    /// Entering this state prevents the task from being respawned while in a timer queue.
+    ///
+    /// Safety:
+    ///
+    /// This functions should only be called by the timer queue driver, before
+    /// enqueueing the timer item.
+    pub unsafe fn timer_enqueue(&self) -> timer_queue::TimerEnqueueOperation {
+        self.header().state.timer_enqueue()
+    }
+
+    /// Unmark the task as timer-queued.
+    ///
+    /// Safety:
+    ///
+    /// This functions should only be called by the timer queue implementation, after the task has
+    /// been removed from the timer queue.
+    pub unsafe fn timer_dequeue(&self) {
+        self.header().state.timer_dequeue()
+    }
+
     /// The returned pointer is valid for the entire TaskStorage.
     pub(crate) fn as_ptr(self) -> *const TaskHeader {
         self.ptr.as_ptr()
@@ -120,9 +157,6 @@ impl<F: Future + 'static> TaskStorage<F> {
                 // Note: this is lazily initialized so that a static `TaskStorage` will go in `.bss`
                 poll_fn: SyncUnsafeCell::new(None),
 
-                #[cfg(feature = "integrated-timers")]
-                expires_at: SyncUnsafeCell::new(0),
-                #[cfg(feature = "integrated-timers")]
                 timer_queue_item: timer_queue::TimerQueueItem::new(),
             },
             future: UninitCell::uninit(),
@@ -159,10 +193,25 @@ impl<F: Future + 'static> TaskStorage<F> {
         match future.poll(&mut cx) {
             Poll::Ready(_) => {
                 this.future.drop_in_place();
+
+                // Mark this task to be timer queued.
+                // We're splitting the enqueue in two parts, so that we can change task state
+                // to something that prevent re-queueing.
+                let op = this.raw.state.timer_enqueue();
+
+                // Now mark the task as not spawned, so that
+                // - it can be spawned again once it has been removed from the timer queue
+                // - it can not be timer-queued again
+                // We must do this before scheduling the wake, to prevent the task from being
+                // dequeued by the time driver while it's still SPAWNED.
                 this.raw.state.despawn();
 
-                #[cfg(feature = "integrated-timers")]
-                this.raw.expires_at.set(u64::MAX);
+                // Now let's finish enqueueing. While we shouldn't get an `Ignore` here, it's
+                // better to be safe.
+                if op == timer_queue::TimerEnqueueOperation::Enqueue {
+                    // Schedule the task in the past, so it gets dequeued ASAP.
+                    unsafe { _embassy_time_schedule_wake(0, &waker) }
+                }
             }
             Poll::Pending => {}
         }
@@ -181,6 +230,10 @@ impl<F: Future + 'static> TaskStorage<F> {
     }
 }
 
+extern "Rust" {
+    fn _embassy_time_schedule_wake(at: u64, waker: &core::task::Waker);
+}
+
 /// An uninitialized [`TaskStorage`].
 pub struct AvailableTask<F: Future + 'static> {
     task: &'static TaskStorage<F>,
@@ -316,34 +369,16 @@ impl Pender {
 pub(crate) struct SyncExecutor {
     run_queue: RunQueue,
     pender: Pender,
-
-    #[cfg(feature = "integrated-timers")]
-    pub(crate) timer_queue: timer_queue::TimerQueue,
-    #[cfg(feature = "integrated-timers")]
-    alarm: AlarmHandle,
 }
 
 impl SyncExecutor {
     pub(crate) fn new(pender: Pender) -> Self {
-        #[cfg(feature = "integrated-timers")]
-        let alarm = unsafe { unwrap!(embassy_time_driver::allocate_alarm()) };
-
         Self {
             run_queue: RunQueue::new(),
             pender,
-
-            #[cfg(feature = "integrated-timers")]
-            timer_queue: timer_queue::TimerQueue::new(),
-            #[cfg(feature = "integrated-timers")]
-            alarm,
         }
     }
 
-    pub(crate) unsafe fn initialize(&'static self) {
-        #[cfg(feature = "integrated-timers")]
-        embassy_time_driver::set_alarm_callback(self.alarm, Self::alarm_callback, self as *const _ as *mut ());
-    }
-
     /// Enqueue a task in the task queue
     ///
     /// # Safety
@@ -360,12 +395,6 @@ impl SyncExecutor {
         }
     }
 
-    #[cfg(feature = "integrated-timers")]
-    fn alarm_callback(ctx: *mut ()) {
-        let this: &Self = unsafe { &*(ctx as *const Self) };
-        this.pender.pend();
-    }
-
     pub(super) unsafe fn spawn(&'static self, task: TaskRef) {
         task.header().executor.set(Some(self));
 
@@ -379,56 +408,27 @@ impl SyncExecutor {
     ///
     /// Same as [`Executor::poll`], plus you must only call this on the thread this executor was created.
     pub(crate) unsafe fn poll(&'static self) {
-        #[allow(clippy::never_loop)]
-        loop {
-            #[cfg(feature = "integrated-timers")]
-            self.timer_queue
-                .dequeue_expired(embassy_time_driver::now(), wake_task_no_pend);
-
-            self.run_queue.dequeue_all(|p| {
-                let task = p.header();
-
-                #[cfg(feature = "integrated-timers")]
-                task.expires_at.set(u64::MAX);
-
-                if !task.state.run_dequeue() {
-                    // If task is not running, ignore it. This can happen in the following scenario:
-                    //   - Task gets dequeued, poll starts
-                    //   - While task is being polled, it gets woken. It gets placed in the queue.
-                    //   - Task poll finishes, returning done=true
-                    //   - RUNNING bit is cleared, but the task is already in the queue.
-                    return;
-                }
-
-                #[cfg(feature = "trace")]
-                trace::task_exec_begin(self, &p);
+        self.run_queue.dequeue_all(|p| {
+            let task = p.header();
+
+            if !task.state.run_dequeue() {
+                // If task is not running, ignore it. This can happen in the following scenario:
+                //   - Task gets dequeued, poll starts
+                //   - While task is being polled, it gets woken. It gets placed in the queue.
+                //   - Task poll finishes, returning done=true
+                //   - RUNNING bit is cleared, but the task is already in the queue.
+                return;
+            }
 
-                // Run the task
-                task.poll_fn.get().unwrap_unchecked()(p);
+            #[cfg(feature = "trace")]
+            trace::task_exec_begin(self, &p);
 
-                #[cfg(feature = "trace")]
-                trace::task_exec_end(self, &p);
+            // Run the task
+            task.poll_fn.get().unwrap_unchecked()(p);
 
-                // Enqueue or update into timer_queue
-                #[cfg(feature = "integrated-timers")]
-                self.timer_queue.update(p);
-            });
-
-            #[cfg(feature = "integrated-timers")]
-            {
-                // If this is already in the past, set_alarm might return false
-                // In that case do another poll loop iteration.
-                let next_expiration = self.timer_queue.next_expiration();
-                if embassy_time_driver::set_alarm(self.alarm, next_expiration) {
-                    break;
-                }
-            }
-
-            #[cfg(not(feature = "integrated-timers"))]
-            {
-                break;
-            }
-        }
+            #[cfg(feature = "trace")]
+            trace::task_exec_end(self, &p);
+        });
 
         #[cfg(feature = "trace")]
         trace::executor_idle(self)
@@ -494,15 +494,6 @@ impl Executor {
         }
     }
 
-    /// Initializes the executor.
-    ///
-    /// # Safety
-    ///
-    /// This function must be called once before any other method is called.
-    pub unsafe fn initialize(&'static self) {
-        self.inner.initialize();
-    }
-
     /// Spawn a task in this executor.
     ///
     /// # Safety
@@ -575,21 +566,3 @@ pub fn wake_task_no_pend(task: TaskRef) {
         }
     }
 }
-
-#[cfg(feature = "integrated-timers")]
-struct TimerQueue;
-
-#[cfg(feature = "integrated-timers")]
-impl embassy_time_queue_driver::TimerQueue for TimerQueue {
-    fn schedule_wake(&'static self, at: u64, waker: &core::task::Waker) {
-        let task = waker::task_from_waker(waker);
-        let task = task.header();
-        unsafe {
-            let expires_at = task.expires_at.get();
-            task.expires_at.set(expires_at.min(at));
-        }
-    }
-}
-
-#[cfg(feature = "integrated-timers")]
-embassy_time_queue_driver::timer_queue_impl!(static TIMER_QUEUE: TimerQueue = TimerQueue);
diff --git a/embassy-executor/src/raw/state_atomics.rs b/embassy-executor/src/raw/state_atomics.rs
index e1279ac0b..15eb9a368 100644
--- a/embassy-executor/src/raw/state_atomics.rs
+++ b/embassy-executor/src/raw/state_atomics.rs
@@ -1,11 +1,12 @@
 use core::sync::atomic::{AtomicU32, Ordering};
 
+use super::timer_queue::TimerEnqueueOperation;
+
 /// Task is spawned (has a future)
 pub(crate) const STATE_SPAWNED: u32 = 1 << 0;
 /// Task is in the executor run queue
 pub(crate) const STATE_RUN_QUEUED: u32 = 1 << 1;
 /// Task is in the executor timer queue
-#[cfg(feature = "integrated-timers")]
 pub(crate) const STATE_TIMER_QUEUED: u32 = 1 << 2;
 
 pub(crate) struct State {
@@ -56,18 +57,31 @@ impl State {
         state & STATE_SPAWNED != 0
     }
 
-    /// Mark the task as timer-queued. Return whether it was newly queued (i.e. not queued before)
-    #[cfg(feature = "integrated-timers")]
+    /// Mark the task as timer-queued. Return whether it can be enqueued.
     #[inline(always)]
-    pub fn timer_enqueue(&self) -> bool {
-        let old_state = self.state.fetch_or(STATE_TIMER_QUEUED, Ordering::AcqRel);
-        old_state & STATE_TIMER_QUEUED == 0
+    pub fn timer_enqueue(&self) -> TimerEnqueueOperation {
+        if self
+            .state
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |state| {
+                // If not started, ignore it
+                if state & STATE_SPAWNED == 0 {
+                    None
+                } else {
+                    // Mark it as enqueued
+                    Some(state | STATE_TIMER_QUEUED)
+                }
+            })
+            .is_ok()
+        {
+            TimerEnqueueOperation::Enqueue
+        } else {
+            TimerEnqueueOperation::Ignore
+        }
     }
 
     /// Unmark the task as timer-queued.
-    #[cfg(feature = "integrated-timers")]
     #[inline(always)]
     pub fn timer_dequeue(&self) {
-        self.state.fetch_and(!STATE_TIMER_QUEUED, Ordering::AcqRel);
+        self.state.fetch_and(!STATE_TIMER_QUEUED, Ordering::Relaxed);
     }
 }
diff --git a/embassy-executor/src/raw/state_atomics_arm.rs b/embassy-executor/src/raw/state_atomics_arm.rs
index e4dfe5093..7a152e8c0 100644
--- a/embassy-executor/src/raw/state_atomics_arm.rs
+++ b/embassy-executor/src/raw/state_atomics_arm.rs
@@ -1,9 +1,12 @@
 use core::arch::asm;
 use core::sync::atomic::{compiler_fence, AtomicBool, AtomicU32, Ordering};
 
+use super::timer_queue::TimerEnqueueOperation;
+
 // Must be kept in sync with the layout of `State`!
 pub(crate) const STATE_SPAWNED: u32 = 1 << 0;
 pub(crate) const STATE_RUN_QUEUED: u32 = 1 << 8;
+pub(crate) const STATE_TIMER_QUEUED: u32 = 1 << 16;
 
 #[repr(C, align(4))]
 pub(crate) struct State {
@@ -87,15 +90,29 @@ impl State {
         r
     }
 
-    /// Mark the task as timer-queued. Return whether it was newly queued (i.e. not queued before)
-    #[cfg(feature = "integrated-timers")]
+    /// Mark the task as timer-queued. Return whether it can be enqueued.
     #[inline(always)]
-    pub fn timer_enqueue(&self) -> bool {
-        !self.timer_queued.swap(true, Ordering::Relaxed)
+    pub fn timer_enqueue(&self) -> TimerEnqueueOperation {
+        if self
+            .as_u32()
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |state| {
+                // If not started, ignore it
+                if state & STATE_SPAWNED == 0 {
+                    None
+                } else {
+                    // Mark it as enqueued
+                    Some(state | STATE_TIMER_QUEUED)
+                }
+            })
+            .is_ok()
+        {
+            TimerEnqueueOperation::Enqueue
+        } else {
+            TimerEnqueueOperation::Ignore
+        }
     }
 
     /// Unmark the task as timer-queued.
-    #[cfg(feature = "integrated-timers")]
     #[inline(always)]
     pub fn timer_dequeue(&self) {
         self.timer_queued.store(false, Ordering::Relaxed);
diff --git a/embassy-executor/src/raw/state_critical_section.rs b/embassy-executor/src/raw/state_critical_section.rs
index c3cc1b0b7..367162ba2 100644
--- a/embassy-executor/src/raw/state_critical_section.rs
+++ b/embassy-executor/src/raw/state_critical_section.rs
@@ -2,12 +2,13 @@ use core::cell::Cell;
 
 use critical_section::Mutex;
 
+use super::timer_queue::TimerEnqueueOperation;
+
 /// Task is spawned (has a future)
 pub(crate) const STATE_SPAWNED: u32 = 1 << 0;
 /// Task is in the executor run queue
 pub(crate) const STATE_RUN_QUEUED: u32 = 1 << 1;
 /// Task is in the executor timer queue
-#[cfg(feature = "integrated-timers")]
 pub(crate) const STATE_TIMER_QUEUED: u32 = 1 << 2;
 
 pub(crate) struct State {
@@ -73,19 +74,22 @@ impl State {
         })
     }
 
-    /// Mark the task as timer-queued. Return whether it was newly queued (i.e. not queued before)
-    #[cfg(feature = "integrated-timers")]
+    /// Mark the task as timer-queued. Return whether it can be enqueued.
     #[inline(always)]
-    pub fn timer_enqueue(&self) -> bool {
+    pub fn timer_enqueue(&self) -> TimerEnqueueOperation {
         self.update(|s| {
-            let ok = *s & STATE_TIMER_QUEUED == 0;
-            *s |= STATE_TIMER_QUEUED;
-            ok
+            // FIXME: we need to split SPAWNED into two phases, to prevent enqueueing a task that is
+            // just being spawned, because its executor pointer may still be changing.
+            if *s & STATE_SPAWNED == STATE_SPAWNED {
+                *s |= STATE_TIMER_QUEUED;
+                TimerEnqueueOperation::Enqueue
+            } else {
+                TimerEnqueueOperation::Ignore
+            }
         })
     }
 
     /// Unmark the task as timer-queued.
-    #[cfg(feature = "integrated-timers")]
     #[inline(always)]
     pub fn timer_dequeue(&self) {
         self.update(|s| *s &= !STATE_TIMER_QUEUED);
diff --git a/embassy-executor/src/raw/timer_queue.rs b/embassy-executor/src/raw/timer_queue.rs
index 94a5f340b..2ba0e00a9 100644
--- a/embassy-executor/src/raw/timer_queue.rs
+++ b/embassy-executor/src/raw/timer_queue.rs
@@ -1,76 +1,39 @@
-use core::cmp::min;
+//! Timer queue operations.
+
+use core::cell::Cell;
 
 use super::TaskRef;
-use crate::raw::util::SyncUnsafeCell;
 
-pub(crate) struct TimerQueueItem {
-    next: SyncUnsafeCell<Option<TaskRef>>,
-}
+/// An item in the timer queue.
+pub struct TimerQueueItem {
+    /// The next item in the queue.
+    ///
+    /// If this field contains `Some`, the item is in the queue. The last item in the queue has a
+    /// value of `Some(dangling_pointer)`
+    pub next: Cell<Option<TaskRef>>,
 
-impl TimerQueueItem {
-    pub const fn new() -> Self {
-        Self {
-            next: SyncUnsafeCell::new(None),
-        }
-    }
+    /// The time at which this item expires.
+    pub expires_at: Cell<u64>,
 }
 
-pub(crate) struct TimerQueue {
-    head: SyncUnsafeCell<Option<TaskRef>>,
-}
+unsafe impl Sync for TimerQueueItem {}
 
-impl TimerQueue {
-    pub const fn new() -> Self {
+impl TimerQueueItem {
+    pub(crate) const fn new() -> Self {
         Self {
-            head: SyncUnsafeCell::new(None),
-        }
-    }
-
-    pub(crate) unsafe fn update(&self, p: TaskRef) {
-        let task = p.header();
-        if task.expires_at.get() != u64::MAX {
-            if task.state.timer_enqueue() {
-                task.timer_queue_item.next.set(self.head.get());
-                self.head.set(Some(p));
-            }
+            next: Cell::new(None),
+            expires_at: Cell::new(0),
         }
     }
+}
 
-    pub(crate) unsafe fn next_expiration(&self) -> u64 {
-        let mut res = u64::MAX;
-        self.retain(|p| {
-            let task = p.header();
-            let expires = task.expires_at.get();
-            res = min(res, expires);
-            expires != u64::MAX
-        });
-        res
-    }
-
-    pub(crate) unsafe fn dequeue_expired(&self, now: u64, on_task: impl Fn(TaskRef)) {
-        self.retain(|p| {
-            let task = p.header();
-            if task.expires_at.get() <= now {
-                on_task(p);
-                false
-            } else {
-                true
-            }
-        });
-    }
-
-    pub(crate) unsafe fn retain(&self, mut f: impl FnMut(TaskRef) -> bool) {
-        let mut prev = &self.head;
-        while let Some(p) = prev.get() {
-            let task = p.header();
-            if f(p) {
-                // Skip to next
-                prev = &task.timer_queue_item.next;
-            } else {
-                // Remove it
-                prev.set(task.timer_queue_item.next.get());
-                task.state.timer_dequeue();
-            }
-        }
-    }
+/// The operation to perform after `timer_enqueue` is called.
+#[derive(Debug, Copy, Clone, PartialEq)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+#[must_use]
+pub enum TimerEnqueueOperation {
+    /// Enqueue the task (or update its expiration time).
+    Enqueue,
+    /// The task must not be enqueued in the timer queue.
+    Ignore,
 }
diff --git a/embassy-executor/src/raw/trace.rs b/embassy-executor/src/raw/trace.rs
index c7bcf9c11..b34387b58 100644
--- a/embassy-executor/src/raw/trace.rs
+++ b/embassy-executor/src/raw/trace.rs
@@ -61,29 +61,23 @@ pub(crate) fn executor_idle(executor: &SyncExecutor) {
     rtos_trace::trace::system_idle();
 }
 
-#[cfg(all(feature = "rtos-trace", feature = "integrated-timers"))]
-const fn gcd(a: u64, b: u64) -> u64 {
-    if b == 0 {
-        a
-    } else {
-        gcd(b, a % b)
-    }
-}
-
 #[cfg(feature = "rtos-trace")]
 impl rtos_trace::RtosTraceOSCallbacks for crate::raw::SyncExecutor {
     fn task_list() {
         // We don't know what tasks exist, so we can't send them.
     }
-    #[cfg(feature = "integrated-timers")]
     fn time() -> u64 {
+        const fn gcd(a: u64, b: u64) -> u64 {
+            if b == 0 {
+                a
+            } else {
+                gcd(b, a % b)
+            }
+        }
+
         const GCD_1M: u64 = gcd(embassy_time_driver::TICK_HZ, 1_000_000);
         embassy_time_driver::now() * (1_000_000 / GCD_1M) / (embassy_time_driver::TICK_HZ / GCD_1M)
     }
-    #[cfg(not(feature = "integrated-timers"))]
-    fn time() -> u64 {
-        0
-    }
 }
 
 #[cfg(feature = "rtos-trace")]