Fixed systick monotonic

rtic-time/.gitignore

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+**/*.rs.bk
+.#*
+.gdb_history
+/target
+Cargo.lock
+*.hex

rtic-time/Cargo.toml

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+[package]
+name = "rtic-time"
+version = "1.0.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+critical-section = "1"
+futures-util = { version = "0.3.25", default-features = false }

rtic-time/rust-toolchain.toml

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+[toolchain]
+channel = "nightly"
+components = [ "rust-src", "rustfmt", "llvm-tools-preview" ]
+targets = [ "thumbv6m-none-eabi", "thumbv7m-none-eabi" ]

rtic-time/src/lib.rs

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+//! Crate
+
+#![no_std]
+#![no_main]
+#![deny(missing_docs)]
+#![allow(incomplete_features)]
+#![feature(async_fn_in_trait)]
+
+pub mod monotonic;
+
+use core::future::{poll_fn, Future};
+use core::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+use core::task::{Poll, Waker};
+use futures_util::{
+    future::{select, Either},
+    pin_mut,
+};
+pub use monotonic::Monotonic;
+
+mod linked_list;
+
+use linked_list::{Link, LinkedList};
+
+/// Holds a waker and at which time instant this waker shall be awoken.
+struct WaitingWaker<Mono: Monotonic> {
+    waker: Waker,
+    release_at: Mono::Instant,
+}
+
+impl<Mono: Monotonic> Clone for WaitingWaker<Mono> {
+    fn clone(&self) -> Self {
+        Self {
+            waker: self.waker.clone(),
+            release_at: self.release_at,
+        }
+    }
+}
+
+impl<Mono: Monotonic> PartialEq for WaitingWaker<Mono> {
+    fn eq(&self, other: &Self) -> bool {
+        self.release_at == other.release_at
+    }
+}
+
+impl<Mono: Monotonic> PartialOrd for WaitingWaker<Mono> {
+    fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
+        self.release_at.partial_cmp(&other.release_at)
+    }
+}
+
+/// A generic timer queue for async executors.
+///
+/// # Blocking
+///
+/// The internal priority queue uses global critical sections to manage access. This means that
+/// `await`ing a delay will cause a lock of the entire system for O(n) time. In practice the lock
+/// duration is ~10 clock cycles per element in the queue.
+///
+/// # Safety
+///
+/// This timer queue is based on an intrusive linked list, and by extension the links are strored
+/// on the async stacks of callers. The links are deallocated on `drop` or when the wait is
+/// complete.
+///
+/// Do not call `mem::forget` on an awaited future, or there will be dragons!
+pub struct TimerQueue<Mono: Monotonic> {
+    queue: LinkedList<WaitingWaker<Mono>>,
+    initialized: AtomicBool,
+}
+
+/// This indicates that there was a timeout.
+pub struct TimeoutError;
+
+impl<Mono: Monotonic> TimerQueue<Mono> {
+    /// Make a new queue.
+    pub const fn new() -> Self {
+        Self {
+            queue: LinkedList::new(),
+            initialized: AtomicBool::new(false),
+        }
+    }
+
+    /// Forwards the `Monotonic::now()` method.
+    #[inline(always)]
+    pub fn now(&self) -> Mono::Instant {
+        Mono::now()
+    }
+
+    /// Takes the initialized monotonic to initialize the TimerQueue.
+    pub fn initialize(&self, monotonic: Mono) {
+        self.initialized.store(true, Ordering::SeqCst);
+
+        // Don't run drop on `Mono`
+        core::mem::forget(monotonic);
+    }
+
+    /// Call this in the interrupt handler of the hardware timer supporting the `Monotonic`
+    ///
+    /// # Safety
+    ///
+    /// It's always safe to call, but it must only be called from the interrupt of the
+    /// monotonic timer for correct operation.
+    pub unsafe fn on_monotonic_interrupt(&self) {
+        Mono::clear_compare_flag();
+        Mono::on_interrupt();
+
+        loop {
+            let mut release_at = None;
+            let head = self.queue.pop_if(|head| {
+                release_at = Some(head.release_at);
+
+                Mono::now() >= head.release_at
+            });
+
+            match (head, release_at) {
+                (Some(link), _) => {
+                    link.waker.wake();
+                }
+                (None, Some(instant)) => {
+                    Mono::enable_timer();
+                    Mono::set_compare(instant);
+
+                    if Mono::now() >= instant {
+                        // The time for the next instant passed while handling it,
+                        // continue dequeueing
+                        continue;
+                    }
+
+                    break;
+                }
+                (None, None) => {
+                    // Queue is empty
+                    Mono::disable_timer();
+
+                    break;
+                }
+            }
+        }
+    }
+
+    /// Timeout at a specific time.
+    pub async fn timeout_at<F: Future>(
+        &self,
+        instant: Mono::Instant,
+        future: F,
+    ) -> Result<F::Output, TimeoutError> {
+        let delay = self.delay_until(instant);
+
+        pin_mut!(future);
+        pin_mut!(delay);
+
+        match select(future, delay).await {
+            Either::Left((r, _)) => Ok(r),
+            Either::Right(_) => Err(TimeoutError),
+        }
+    }
+
+    /// Timeout after a specific duration.
+    #[inline]
+    pub async fn timeout_after<F: Future>(
+        &self,
+        duration: Mono::Duration,
+        future: F,
+    ) -> Result<F::Output, TimeoutError> {
+        self.timeout_at(Mono::now() + duration, future).await
+    }
+
+    /// Delay for some duration of time.
+    #[inline]
+    pub async fn delay(&self, duration: Mono::Duration) {
+        let now = Mono::now();
+
+        self.delay_until(now + duration).await;
+    }
+
+    /// Delay to some specific time instant.
+    pub async fn delay_until(&self, instant: Mono::Instant) {
+        if !self.initialized.load(Ordering::Relaxed) {
+            panic!(
+                "The timer queue is not initialized with a monotonic, you need to run `initialize`"
+            );
+        }
+
+        let mut first_run = true;
+        let queue = &self.queue;
+        let mut link = Link::new(WaitingWaker {
+            waker: poll_fn(|cx| Poll::Ready(cx.waker().clone())).await,
+            release_at: instant,
+        });
+
+        let marker = &AtomicUsize::new(0);
+
+        let dropper = OnDrop::new(|| {
+            queue.delete(marker.load(Ordering::Relaxed));
+        });
+
+        poll_fn(|_| {
+            if Mono::now() >= instant {
+                return Poll::Ready(());
+            }
+
+            if first_run {
+                first_run = false;
+                let (was_empty, addr) = queue.insert(&mut link);
+                marker.store(addr, Ordering::Relaxed);
+
+                if was_empty {
+                    // Pend the monotonic handler if the queue was empty to setup the timer.
+                    Mono::pend_interrupt();
+                }
+            }
+
+            Poll::Pending
+        })
+        .await;
+
+        // Make sure that our link is deleted from the list before we drop this stack
+        drop(dropper);
+    }
+}
+
+struct OnDrop<F: FnOnce()> {
+    f: core::mem::MaybeUninit<F>,
+}
+
+impl<F: FnOnce()> OnDrop<F> {
+    pub fn new(f: F) -> Self {
+        Self {
+            f: core::mem::MaybeUninit::new(f),
+        }
+    }
+
+    #[allow(unused)]
+    pub fn defuse(self) {
+        core::mem::forget(self)
+    }
+}
+
+impl<F: FnOnce()> Drop for OnDrop<F> {
+    fn drop(&mut self) {
+        unsafe { self.f.as_ptr().read()() }
+    }
+}
+
+// -------- Test program ---------
+//
+//
+// use systick_monotonic::{Systick, TimerQueue};
+//
+// // same panicking *behavior* as `panic-probe` but doesn't print a panic message
+// // this prevents the panic message being printed *twice* when `defmt::panic` is invoked
+// #[defmt::panic_handler]
+// fn panic() -> ! {
+//     cortex_m::asm::udf()
+// }
+//
+// /// Terminates the application and makes `probe-run` exit with exit-code = 0
+// pub fn exit() -> ! {
+//     loop {
+//         cortex_m::asm::bkpt();
+//     }
+// }
+//
+// defmt::timestamp!("{=u64:us}", {
+//     let time_us: fugit::MicrosDurationU32 = MONO.now().duration_since_epoch().convert();
+//
+//     time_us.ticks() as u64
+// });
+//
+// make_systick_timer_queue!(MONO, Systick<1_000>);
+//
+// #[rtic::app(
+//     device = nrf52832_hal::pac,
+//     dispatchers = [SWI0_EGU0, SWI1_EGU1, SWI2_EGU2, SWI3_EGU3, SWI4_EGU4, SWI5_EGU5],
+// )]
+// mod app {
+//     use super::{Systick, MONO};
+//     use fugit::ExtU32;
+//
+//     #[shared]
+//     struct Shared {}
+//
+//     #[local]
+//     struct Local {}
+//
+//     #[init]
+//     fn init(cx: init::Context) -> (Shared, Local) {
+//         defmt::println!("init");
+//
+//         let systick = Systick::start(cx.core.SYST, 64_000_000);
+//
+//         defmt::println!("initializing monotonic");
+//
+//         MONO.initialize(systick);
+//
+//         async_task::spawn().ok();
+//         async_task2::spawn().ok();
+//         async_task3::spawn().ok();
+//
+//         (Shared {}, Local {})
+//     }
+//
+//     #[idle]
+//     fn idle(_: idle::Context) -> ! {
+//         defmt::println!("idle");
+//
+//         loop {
+//             core::hint::spin_loop();
+//         }
+//     }
+//
+//     #[task]
+//     async fn async_task(_: async_task::Context) {
+//         loop {
+//             defmt::println!("async task waiting for 1 second");
+//             MONO.delay(1.secs()).await;
+//         }
+//     }
+//
+//     #[task]
+//     async fn async_task2(_: async_task2::Context) {
+//         loop {
+//             defmt::println!("    async task 2 waiting for 0.5 second");
+//             MONO.delay(500.millis()).await;
+//         }
+//     }
+//
+//     #[task]
+//     async fn async_task3(_: async_task3::Context) {
+//         loop {
+//             defmt::println!("        async task 3 waiting for 0.2 second");
+//             MONO.delay(200.millis()).await;
+//         }
+//     }
+// }
+//

rtic-time/src/linked_list.rs

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+//! ...
+
+use core::marker::PhantomPinned;
+use core::sync::atomic::{AtomicPtr, Ordering};
+use critical_section as cs;
+
+/// A sorted linked list for the timer queue.
+pub struct LinkedList<T> {
+    head: AtomicPtr<Link<T>>,
+}
+
+impl<T> LinkedList<T> {
+    /// Create a new linked list.
+    pub const fn new() -> Self {
+        Self {
+            head: AtomicPtr::new(core::ptr::null_mut()),
+        }
+    }
+}
+
+impl<T: PartialOrd + Clone> LinkedList<T> {
+    /// Pop the first element in the queue if the closure returns true.
+    pub fn pop_if<F: FnOnce(&T) -> bool>(&self, f: F) -> Option<T> {
+        cs::with(|_| {
+            // Make sure all previous writes are visible
+            core::sync::atomic::fence(Ordering::SeqCst);
+
+            let head = self.head.load(Ordering::Relaxed);
+
+            // SAFETY: `as_ref` is safe as `insert` requires a valid reference to a link
+            if let Some(head) = unsafe { head.as_ref() } {
+                if f(&head.val) {
+                    // Move head to the next element
+                    self.head
+                        .store(head.next.load(Ordering::Relaxed), Ordering::Relaxed);
+
+                    // We read the value at head
+                    let head_val = head.val.clone();
+
+                    return Some(head_val);
+                }
+            }
+            None
+        })
+    }
+
+    /// Delete a link at an address.
+    pub fn delete(&self, addr: usize) {
+        cs::with(|_| {
+            // Make sure all previous writes are visible
+            core::sync::atomic::fence(Ordering::SeqCst);
+
+            let head = self.head.load(Ordering::Relaxed);
+
+            // SAFETY: `as_ref` is safe as `insert` requires a valid reference to a link
+            let head_ref = if let Some(head_ref) = unsafe { head.as_ref() } {
+                head_ref
+            } else {
+                // 1. List is empty, do nothing
+                return;
+            };
+
+            if head as *const _ as usize == addr {
+                // 2. Replace head with head.next
+                self.head
+                    .store(head_ref.next.load(Ordering::Relaxed), Ordering::Relaxed);
+
+                return;
+            }
+
+            // 3. search list for correct node
+            let mut curr = head_ref;
+            let mut next = head_ref.next.load(Ordering::Relaxed);
+
+            // SAFETY: `as_ref` is safe as `insert` requires a valid reference to a link
+            while let Some(next_link) = unsafe { next.as_ref() } {
+                // Next is not null
+
+                if next as *const _ as usize == addr {
+                    curr.next
+                        .store(next_link.next.load(Ordering::Relaxed), Ordering::Relaxed);
+
+                    return;
+                }
+
+                // Continue searching
+                curr = next_link;
+                next = next_link.next.load(Ordering::Relaxed);
+            }
+        })
+    }
+
+    /// Insert a new link into the linked list.
+    /// The return is (was_empty, address), where the address of the link is for use with `delete`.
+    pub fn insert(&self, val: &mut Link<T>) -> (bool, usize) {
+        cs::with(|_| {
+            let addr = val as *const _ as usize;
+
+            // Make sure all previous writes are visible
+            core::sync::atomic::fence(Ordering::SeqCst);
+
+            let head = self.head.load(Ordering::Relaxed);
+
+            // 3 cases to handle
+
+            // 1. List is empty, write to head
+            // SAFETY: `as_ref` is safe as `insert` requires a valid reference to a link
+            let head_ref = if let Some(head_ref) = unsafe { head.as_ref() } {
+                head_ref
+            } else {
+                self.head.store(val, Ordering::Relaxed);
+                return (true, addr);
+            };
+
+            // 2. val needs to go in first
+            if val.val < head_ref.val {
+                // Set current head as next of `val`
+                val.next.store(head, Ordering::Relaxed);
+
+                // `val` is now first in the queue
+                self.head.store(val, Ordering::Relaxed);
+
+                return (false, addr);
+            }
+
+            // 3. search list for correct place
+            let mut curr = head_ref;
+            let mut next = head_ref.next.load(Ordering::Relaxed);
+
+            // SAFETY: `as_ref` is safe as `insert` requires a valid reference to a link
+            while let Some(next_link) = unsafe { next.as_ref() } {
+                // Next is not null
+
+                if val.val < next_link.val {
+                    // Replace next with `val`
+                    val.next.store(next, Ordering::Relaxed);
+
+                    // Insert `val`
+                    curr.next.store(val, Ordering::Relaxed);
+
+                    return (false, addr);
+                }
+
+                // Continue searching
+                curr = next_link;
+                next = next_link.next.load(Ordering::Relaxed);
+            }
+
+            // No next, write link to last position in list
+            curr.next.store(val, Ordering::Relaxed);
+
+            (false, addr)
+        })
+    }
+}
+
+/// A link in the linked list.
+pub struct Link<T> {
+    val: T,
+    next: AtomicPtr<Link<T>>,
+    _up: PhantomPinned,
+}
+
+impl<T> Link<T> {
+    /// Create a new link.
+    pub const fn new(val: T) -> Self {
+        Self {
+            val,
+            next: AtomicPtr::new(core::ptr::null_mut()),
+            _up: PhantomPinned,
+        }
+    }
+}

rtic-time/src/monotonic.rs

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+//! ...
+
+/// # A monotonic clock / counter definition.
+///
+/// ## Correctness
+///
+/// The trait enforces that proper time-math is implemented between `Instant` and `Duration`. This
+/// is a requirement on the time library that the user chooses to use.
+pub trait Monotonic {
+    /// The time at time zero.
+    const ZERO: Self::Instant;
+
+    /// The type for instant, defining an instant in time.
+    ///
+    /// **Note:** In all APIs in RTIC that use instants from this monotonic, this type will be used.
+    type Instant: Ord
+        + Copy
+        + core::ops::Add<Self::Duration, Output = Self::Instant>
+        + core::ops::Sub<Self::Duration, Output = Self::Instant>
+        + core::ops::Sub<Self::Instant, Output = Self::Duration>;
+
+    /// The type for duration, defining an duration of time.
+    ///
+    /// **Note:** In all APIs in RTIC that use duration from this monotonic, this type will be used.
+    type Duration;
+
+    /// Get the current time.
+    fn now() -> Self::Instant;
+
+    /// Set the compare value of the timer interrupt.
+    ///
+    /// **Note:** This method does not need to handle race conditions of the monotonic, the timer
+    /// queue in RTIC checks this.
+    fn set_compare(instant: Self::Instant);
+
+    /// Clear the compare interrupt flag.
+    fn clear_compare_flag();
+
+    /// Pend the timer's interrupt.
+    fn pend_interrupt();
+
+    /// Optional. Runs on interrupt before any timer queue handling.
+    fn on_interrupt() {}
+
+    /// Optional. This is used to save power, this is called when the timer queue is not empty.
+    ///
+    /// Enabling and disabling the monotonic needs to propagate to `now` so that an instant
+    /// based of `now()` is still valid.
+    ///
+    /// NOTE: This may be called more than once.
+    fn enable_timer() {}
+
+    /// Optional. This is used to save power, this is called when the timer queue is empty.
+    ///
+    /// Enabling and disabling the monotonic needs to propagate to `now` so that an instant
+    /// based of `now()` is still valid.
+    ///
+    /// NOTE: This may be called more than once.
+    fn disable_timer() {}
+}