1 files changed, 221 insertions, 0 deletions
diff --git a/src/cyccnt.rs b/src/cyccnt.rs
new file mode 100644
index 0000000..8e07b00
--- /dev/null
+++ b/src/cyccnt.rs
@@ -0,0 +1,221 @@
+//! Data Watchpoint Trace (DWT) unit's CYCle CouNTer (CYCCNT)
+
+use core::{
+    cmp::Ordering,
+    convert::{Infallible, TryInto},
+    fmt, ops,
+};
+
+use cortex_m::peripheral::DWT;
+
+use crate::Fraction;
+
+/// A measurement of the CYCCNT. Opaque and useful only with `Duration`
+///
+/// This data type is only available on ARMv7-M
+///
+/// # Correctness
+///
+/// Adding or subtracting a `Duration` of more than `(1 << 31)` cycles to an `Instant` effectively
+/// makes it "wrap around" and creates an incorrect value. This is also true if the operation is
+/// done in steps, e.g. `(instant + dur) + dur` where `dur` is `(1 << 30)` ticks.
+#[derive(Clone, Copy, Eq, PartialEq)]
+pub struct Instant {
+    inner: i32,
+}
+
+impl Instant {
+    /// Returns an instant corresponding to "now"
+    ///
+    /// *HEADS UP* this function can, and will, return nonsensical values if called within `init`.
+    /// Only use it in `idle` and tasks. In `init`, use the `init::Context.start` field, or the
+    /// `CYCCNT::zero` function, instead of this function
+    pub fn now() -> Self {
+        Instant {
+            inner: DWT::get_cycle_count() as i32,
+        }
+    }
+
+    /// Returns the amount of time elapsed since this instant was created.
+    pub fn elapsed(&self) -> Duration {
+        let diff = Instant::now().inner.wrapping_sub(self.inner);
+        assert!(diff >= 0, "instant now is earlier than self");
+        Duration { inner: diff as u32 }
+    }
+
+    /// Returns the amount of time elapsed from another instant to this one.
+    pub fn duration_since(&self, earlier: Instant) -> Duration {
+        let diff = self.inner.wrapping_sub(earlier.inner);
+        assert!(diff >= 0, "second instant is later than self");
+        Duration { inner: diff as u32 }
+    }
+}
+
+impl fmt::Debug for Instant {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("Instant")
+            .field(&(self.inner as u32))
+            .finish()
+    }
+}
+
+impl ops::AddAssign<Duration> for Instant {
+    fn add_assign(&mut self, dur: Duration) {
+        // NOTE this is a debug assertion because there's no foolproof way to detect a wrap around;
+        // the user may write `(instant + dur) + dur` where `dur` is `(1<<31)-1` ticks.
+        debug_assert!(dur.inner < (1 << 31));
+        self.inner = self.inner.wrapping_add(dur.inner as i32);
+    }
+}
+
+impl ops::Add<Duration> for Instant {
+    type Output = Self;
+
+    fn add(mut self, dur: Duration) -> Self {
+        self += dur;
+        self
+    }
+}
+
+impl ops::SubAssign<Duration> for Instant {
+    fn sub_assign(&mut self, dur: Duration) {
+        // NOTE see the NOTE in `<Instant as AddAssign<Duration>>::add_assign`
+        debug_assert!(dur.inner < (1 << 31));
+        self.inner = self.inner.wrapping_sub(dur.inner as i32);
+    }
+}
+
+impl ops::Sub<Duration> for Instant {
+    type Output = Self;
+
+    fn sub(mut self, dur: Duration) -> Self {
+        self -= dur;
+        self
+    }
+}
+
+impl ops::Sub<Instant> for Instant {
+    type Output = Duration;
+
+    fn sub(self, other: Instant) -> Duration {
+        self.duration_since(other)
+    }
+}
+
+impl Ord for Instant {
+    fn cmp(&self, rhs: &Self) -> Ordering {
+        self.inner.wrapping_sub(rhs.inner).cmp(&0)
+    }
+}
+
+impl PartialOrd for Instant {
+    fn partial_cmp(&self, rhs: &Self) -> Option<Ordering> {
+        Some(self.cmp(rhs))
+    }
+}
+
+/// A `Duration` type to represent a span of time.
+///
+/// This data type is only available on ARMv7-M
+///
+/// # Correctness
+///
+/// This type is *not* appropriate for representing time spans in the order of, or larger than,
+/// seconds because it can hold a maximum of `(1 << 31)` "ticks" where each tick is the inverse of
+/// the CPU frequency, which usually is dozens of MHz.
+#[derive(Clone, Copy, Default, Eq, Ord, PartialEq, PartialOrd)]
+pub struct Duration {
+    inner: u32,
+}
+
+impl Duration {
+    /// Creates a new `Duration` from the specified number of clock cycles
+    pub fn from_cycles(cycles: u32) -> Self {
+        Duration { inner: cycles }
+    }
+
+    /// Returns the total number of clock cycles contained by this `Duration`
+    pub fn as_cycles(&self) -> u32 {
+        self.inner
+    }
+}
+
+impl TryInto<u32> for Duration {
+    type Error = Infallible;
+
+    fn try_into(self) -> Result<u32, Infallible> {
+        Ok(self.as_cycles())
+    }
+}
+
+impl ops::AddAssign for Duration {
+    fn add_assign(&mut self, dur: Duration) {
+        self.inner += dur.inner;
+    }
+}
+
+impl ops::Add<Duration> for Duration {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        Duration {
+            inner: self.inner + other.inner,
+        }
+    }
+}
+
+impl ops::SubAssign for Duration {
+    fn sub_assign(&mut self, rhs: Duration) {
+        self.inner -= rhs.inner;
+    }
+}
+
+impl ops::Sub<Duration> for Duration {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self {
+        Duration {
+            inner: self.inner - rhs.inner,
+        }
+    }
+}
+
+/// Adds the `cycles` method to the `u32` type
+///
+/// This trait is only available on ARMv7-M
+pub trait U32Ext {
+    /// Converts the `u32` value into clock cycles
+    fn cycles(self) -> Duration;
+}
+
+impl U32Ext for u32 {
+    fn cycles(self) -> Duration {
+        Duration { inner: self }
+    }
+}
+
+/// Implementation of the `Monotonic` trait based on CYCle CouNTer
+pub struct CYCCNT;
+
+impl crate::Monotonic for CYCCNT {
+    type Instant = Instant;
+
+    fn ratio() -> Fraction {
+        Fraction {
+            numerator: 1,
+            denominator: 1,
+        }
+    }
+
+    unsafe fn reset() {
+        (0xE0001004 as *mut u32).write_volatile(0)
+    }
+
+    fn now() -> Instant {
+        Instant::now()
+    }
+
+    fn zero() -> Instant {
+        Instant { inner: 0 }
+    }
+}