Readd MonoTimer

This was accidentally removed in stm32-rs#192

CHANGELOG.md

@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
-No changes.
+### Added
+
+- Readd MonoTimer. This was accidentally removed before. [#247]
 
 ## [v0.7.0] - 2021-06-18
 
@@ -333,6 +335,7 @@ let clocks = rcc
 [defmt]: https://github.com/knurling-rs/defmt
 [filter]: https://defmt.ferrous-systems.com/filtering.html
 
+[#247]: https://github.com/stm32-rs/stm32f3xx-hal/pull/247
 [#238]: https://github.com/stm32-rs/stm32f3xx-hal/pull/238
 [#234]: https://github.com/stm32-rs/stm32f3xx-hal/pull/234
 [#232]: https://github.com/stm32-rs/stm32f3xx-hal/pull/232

src/timer.rs

@@ -8,6 +8,9 @@
 
 use core::convert::{From, TryFrom};
 
+use cortex_m::peripheral::DWT;
+use void::Void;
+
 use crate::hal::timer::{CountDown, Periodic};
 #[cfg(any(
     feature = "stm32f301",
@@ -58,7 +61,51 @@ use crate::pac::{TIM15, TIM16, TIM17, TIM2, TIM6};
 use crate::pac::{TIM3, TIM7};
 use crate::rcc::{Clocks, APB1, APB2};
 use crate::time::rate::*;
-use void::Void;
+
+/// A monotonic nondecreasing timer.
+#[derive(Clone, Copy)]
+pub struct MonoTimer {
+    frequency: Hertz,
+}
+
+impl MonoTimer {
+    /// Creates a new `Monotonic` timer
+    pub fn new(mut dwt: DWT, clocks: Clocks) -> Self {
+        dwt.enable_cycle_counter();
+
+        // now the CYCCNT counter can't be stopped or resetted
+        drop(dwt);
+
+        MonoTimer {
+            frequency: clocks.hclk(),
+        }
+    }
+
+    /// Returns the frequency at which the monotonic timer is operating at
+    pub fn frequency(self) -> Hertz {
+        self.frequency
+    }
+
+    /// Returns an `Instant` corresponding to "now"
+    pub fn now(self) -> Instant {
+        Instant {
+            now: DWT::get_cycle_count(),
+        }
+    }
+}
+
+/// A measurement of a monotonically nondecreasing clock
+#[derive(Clone, Copy)]
+pub struct Instant {
+    now: u32,
+}
+
+impl Instant {
+    /// Ticks elapsed since the `Instant` was created
+    pub fn elapsed(self) -> u32 {
+        DWT::get_cycle_count().wrapping_sub(self.now)
+    }
+}
 
 /// Associated clocks with timers
 pub trait PclkSrc {