Merge #694

694: RTIC 2 r=AfoHT a=korken89



Co-authored-by: Emil Fresk <emil.fresk@gmail.com>
Co-authored-by: Per Lindgren <per.lindgren@ltu.se>

7 files changed, 563 insertions, 0 deletions

diff --git a/rtic-time/.gitignore b/rtic-time/.gitignore
new file mode 100644
index 0000000..c400256
--- /dev/null
+++ b/rtic-time/.gitignore
@@ -0,0 +1,6 @@
+**/*.rs.bk
+.#*
+.gdb_history
+/target
+Cargo.lock
+*.hex
diff --git a/rtic-time/CHANGELOG.md b/rtic-time/CHANGELOG.md
new file mode 100644
index 0000000..d3a9d84
--- /dev/null
+++ b/rtic-time/CHANGELOG.md
@@ -0,0 +1,16 @@
+# Change Log
+
+All notable changes to this project will be documented in this file.
+This project adheres to [Semantic Versioning](http://semver.org/).
+
+For each category, *Added*, *Changed*, *Fixed* add new entries at the top!
+
+## [Unreleased]
+
+### Added
+
+### Changed
+
+### Fixed
+
+## [v1.0.0] - 2023-xx-xx
diff --git a/rtic-time/Cargo.toml b/rtic-time/Cargo.toml
new file mode 100644
index 0000000..c7d13bb
--- /dev/null
+++ b/rtic-time/Cargo.toml
@@ -0,0 +1,22 @@
+[package]
+name = "rtic-time"
+version = "1.0.0-alpha.0"
+
+edition = "2021"
+authors = [
+  "The Real-Time Interrupt-driven Concurrency developers",
+  "Emil Fresk <emil.fresk@gmail.com>",
+  "Henrik Tjäder <henrik@tjaders.com>",
+  "Jorge Aparicio <jorge@japaric.io>",
+  "Per Lindgren <per.lindgren@ltu.se>",
+]
+categories = ["concurrency", "embedded", "no-std", "asynchronous"]
+description = "rtic-time lib TODO"
+license = "MIT OR Apache-2.0"
+
+# 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-common = { version = "1.0.0-alpha.0", path = "../rtic-common" }
diff --git a/rtic-time/rust-toolchain.toml b/rtic-time/rust-toolchain.toml
new file mode 100644
index 0000000..e28b55d
--- /dev/null
+++ b/rtic-time/rust-toolchain.toml
@@ -0,0 +1,4 @@
+[toolchain]
+channel = "nightly"
+components = [ "rust-src", "rustfmt", "llvm-tools-preview" ]
+targets = [ "thumbv6m-none-eabi", "thumbv7m-none-eabi" ]
diff --git a/rtic-time/src/lib.rs b/rtic-time/src/lib.rs
new file mode 100644
index 0000000..78b57a4
--- /dev/null
+++ b/rtic-time/src/lib.rs
@@ -0,0 +1,273 @@
+//! Crate
+
+#![no_std]
+#![deny(missing_docs)]
+//deny_warnings_placeholder_for_ci
+#![allow(incomplete_features)]
+#![feature(async_fn_in_trait)]
+
+use core::future::{poll_fn, Future};
+use core::pin::Pin;
+use core::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+use core::task::{Poll, Waker};
+use futures_util::{
+    future::{select, Either},
+    pin_mut,
+};
+use linked_list::{Link, LinkedList};
+pub use monotonic::Monotonic;
+use rtic_common::dropper::OnDrop;
+
+mod linked_list;
+mod monotonic;
+
+/// Holds a waker and at which time instant this waker shall be awoken.
+struct WaitingWaker<Mono: Monotonic> {
+    waker: Waker,
+    release_at: Mono::Instant,
+    was_poped: AtomicBool,
+}
+
+impl<Mono: Monotonic> Clone for WaitingWaker<Mono> {
+    fn clone(&self) -> Self {
+        Self {
+            waker: self.waker.clone(),
+            release_at: self.release_at,
+            was_poped: AtomicBool::new(self.was_poped.load(Ordering::Relaxed)),
+        }
+    }
+}
+
+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;
+
+/// This is needed to make the async closure in `delay_until` accept that we "share"
+/// the link possible between threads.
+struct LinkPtr<Mono: Monotonic>(*mut Option<linked_list::Link<WaitingWaker<Mono>>>);
+
+impl<Mono: Monotonic> Clone for LinkPtr<Mono> {
+    fn clone(&self) -> Self {
+        LinkPtr(self.0)
+    }
+}
+
+impl<Mono: Monotonic> LinkPtr<Mono> {
+    /// This will dereference the pointer stored within and give out an `&mut`.
+    unsafe fn get(&mut self) -> &mut Option<linked_list::Link<WaitingWaker<Mono>>> {
+        &mut *self.0
+    }
+}
+
+unsafe impl<Mono: Monotonic> Send for LinkPtr<Mono> {}
+unsafe impl<Mono: Monotonic> Sync for LinkPtr<Mono> {}
+
+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);
+
+                let should_pop = Mono::now() >= head.release_at;
+                head.was_poped.store(should_pop, Ordering::Relaxed);
+
+                should_pop
+            });
+
+            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 link_ptr: Option<linked_list::Link<WaitingWaker<Mono>>> = None;
+
+        // Make this future `Drop`-safe
+        // SAFETY(link_ptr): Shadow the original definition of `link_ptr` so we can't abuse it.
+        let mut link_ptr =
+            LinkPtr(&mut link_ptr as *mut Option<linked_list::Link<WaitingWaker<Mono>>>);
+        let mut link_ptr2 = link_ptr.clone();
+
+        let queue = &self.queue;
+        let marker = &AtomicUsize::new(0);
+
+        let dropper = OnDrop::new(|| {
+            queue.delete(marker.load(Ordering::Relaxed));
+        });
+
+        poll_fn(|cx| {
+            if Mono::now() >= instant {
+                return Poll::Ready(());
+            }
+
+            // SAFETY: This pointer is only dereferenced here and on drop of the future
+            // which happens outside this `poll_fn`'s stack frame, so this mutable access cannot
+            // happen at the same time as `dropper` runs.
+            let link = unsafe { link_ptr2.get() };
+            if link.is_none() {
+                let link_ref = link.insert(Link::new(WaitingWaker {
+                    waker: cx.waker().clone(),
+                    release_at: instant,
+                    was_poped: AtomicBool::new(false),
+                }));
+
+                // SAFETY(new_unchecked): The address to the link is stable as it is defined
+                //outside this stack frame.
+                // SAFETY(insert): `link_ref` lifetime comes from `link_ptr` that is shadowed, and
+                // we make sure in `dropper` that the link is removed from the queue before
+                // dropping `link_ptr` AND `dropper` makes sure that the shadowed `link_ptr` lives
+                // until the end of the stack frame.
+                let (was_empty, addr) = unsafe { queue.insert(Pin::new_unchecked(link_ref)) };
+
+                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;
+
+        // SAFETY: We only run this and dereference the pointer if we have
+        // exited the `poll_fn` below in the `drop(dropper)` call. The other dereference
+        // of this pointer is in the `poll_fn`.
+        if let Some(link) = unsafe { link_ptr.get() } {
+            if link.val.was_poped.load(Ordering::Relaxed) {
+                // If it was poped from the queue there is no need to run delete
+                dropper.defuse();
+            }
+        } else {
+            // Make sure that our link is deleted from the list before we drop this stack
+            drop(dropper);
+        }
+    }
+}
diff --git a/rtic-time/src/linked_list.rs b/rtic-time/src/linked_list.rs
new file mode 100644
index 0000000..d4256c9
--- /dev/null
+++ b/rtic-time/src/linked_list.rs
@@ -0,0 +1,182 @@
+//! ...
+
+use core::marker::PhantomPinned;
+use core::pin::Pin;
+use core::sync::atomic::{AtomicPtr, Ordering};
+use critical_section as cs;
+
+/// A sorted linked list for the timer queue.
+pub(crate) 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`.
+    ///
+    /// SAFETY: The pinned link must live until it is removed from this list.
+    pub unsafe fn insert(&self, val: Pin<&Link<T>>) -> (bool, usize) {
+        cs::with(|_| {
+            // SAFETY: This datastructure does not move the underlying value.
+            let val = val.get_ref();
+            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 as *const _ as *mut _, 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 as *const _ as *mut _, 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 as *const _ as *mut _, 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 as *const _ as *mut _, Ordering::Relaxed);
+
+            (false, addr)
+        })
+    }
+}
+
+/// A link in the linked list.
+pub struct Link<T> {
+    pub(crate) 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,
+        }
+    }
+}
diff --git a/rtic-time/src/monotonic.rs b/rtic-time/src/monotonic.rs
new file mode 100644
index 0000000..9b3742f
--- /dev/null
+++ b/rtic-time/src/monotonic.rs
@@ -0,0 +1,60 @@
+//! ...
+
+/// # 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() {}
+}