Monotonic rewrite (#874)

* Rework timer_queue and monotonic architecture

Goals:
 * make Monotonic purely internal
 * make Monotonic purely tick passed, no fugit involved
 * create a wrapper struct in the user's code via a macro that then
   converts the "now" from the tick based monotonic to a fugit based
   timestamp

We need to proxy the delay functions of the timer queue anyway,
so we could simply perform the conversion in those proxy functions.

* Update cargo.lock

* Update readme of rtic-time

* CI: ESP32: Redact esp_image: Too volatile

* Fixup: Changelog double entry rebase mistake

---------

Co-authored-by: Henrik Tjäder <henrik@tjaders.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/rtic-time/src/timer_queue/backend.rs b/rtic-time/src/timer_queue/backend.rs
new file mode 100644
index 0000000..5b71b7c
--- /dev/null
+++ b/rtic-time/src/timer_queue/backend.rs
@@ -0,0 +1,44 @@
+use super::{TimerQueue, TimerQueueTicks};
+
+/// A backend definition for a monotonic clock/counter.
+pub trait TimerQueueBackend: 'static + Sized {
+    /// The type for ticks.
+    type Ticks: TimerQueueTicks;
+
+    /// Get the current time.
+    fn now() -> Self::Ticks;
+
+    /// 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::Ticks);
+
+    /// 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() {}
+
+    /// Returns a reference to the underlying timer queue.
+    fn timer_queue() -> &'static TimerQueue<Self>;
+}