Add 64-bit rtc driver with alarm support.

1 files changed, 204 insertions, 0 deletions

diff --git a/embassy-nrf/src/rtc.rs b/embassy-nrf/src/rtc.rs
new file mode 100644
index 000000000..a5810eb5e
--- /dev/null
+++ b/embassy-nrf/src/rtc.rs
@@ -0,0 +1,204 @@
+use core::cell::Cell;
+use core::ops::Deref;
+use core::sync::atomic::{AtomicU32, Ordering};
+
+use defmt::trace;
+
+use crate::interrupt;
+use crate::interrupt::Mutex;
+use crate::pac::{rtc0, Interrupt, RTC0, RTC1};
+
+#[cfg(any(feature = "52832", feature = "52833", feature = "52840"))]
+use crate::pac::RTC2;
+
+fn calc_now(period: u32, counter: u32) -> u64 {
+    let shift = ((period & 1) << 23) + 0x400000;
+    let counter_shifted = (counter + shift) & 0xFFFFFF;
+    ((period as u64) << 23) + counter_shifted as u64 - 0x400000
+}
+
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_calc_now() {
+        assert_eq!(calc_now(0, 0x000000), 0x0_000000);
+        assert_eq!(calc_now(0, 0x000001), 0x0_000001);
+        assert_eq!(calc_now(0, 0x7FFFFF), 0x0_7FFFFF);
+        assert_eq!(calc_now(1, 0x7FFFFF), 0x0_7FFFFF);
+        assert_eq!(calc_now(0, 0x800000), 0x0_800000);
+        assert_eq!(calc_now(1, 0x800000), 0x0_800000);
+        assert_eq!(calc_now(1, 0x800001), 0x0_800001);
+        assert_eq!(calc_now(1, 0xFFFFFF), 0x0_FFFFFF);
+        assert_eq!(calc_now(2, 0xFFFFFF), 0x0_FFFFFF);
+        assert_eq!(calc_now(1, 0x000000), 0x1_000000);
+        assert_eq!(calc_now(2, 0x000000), 0x1_000000);
+    }
+}
+
+pub struct RTC<T> {
+    rtc: T,
+
+    /// Number of 2^23 periods elapsed since boot.
+    ///
+    /// This is incremented by 1
+    /// - on overflow (counter value 0)
+    /// - on "midway" between overflows (at counter value 0x800000)
+    ///
+    /// Therefore: When even, counter is in 0..0x7fffff. When odd, counter is in 0x800000..0xFFFFFF
+    /// This allows for now() to return the correct value even if it races an overflow.
+    ///
+    /// It overflows on 2^32 * 2^23 / 32768 seconds of uptime, which is 34865 years.
+    period: AtomicU32,
+
+    /// Timestamp at which to fire alarm. u64::MAX if no alarm is scheduled.
+    alarm: Mutex<Cell<u64>>,
+}
+
+impl<T: Instance> RTC<T> {
+    pub fn new(rtc: T) -> Self {
+        Self {
+            rtc,
+            period: AtomicU32::new(0),
+            alarm: Mutex::new(Cell::new(u64::MAX)),
+        }
+    }
+
+    pub fn start(&'static self) {
+        self.rtc.cc[0].write(|w| unsafe { w.bits(0x800000) });
+
+        self.rtc.intenset.write(|w| {
+            let w = w.ovrflw().set();
+            let w = w.compare0().set();
+            w
+        });
+
+        self.rtc.tasks_clear.write(|w| w.tasks_clear().set_bit());
+        self.rtc.tasks_start.write(|w| w.tasks_start().set_bit());
+
+        // Wait for clear
+        while self.rtc.counter.read().bits() != 0 {}
+
+        T::set_rtc_instance(self);
+        interrupt::enable(T::INTERRUPT);
+    }
+
+    fn on_interrupt(&self) {
+        if self.rtc.events_ovrflw.read().bits() == 1 {
+            self.rtc.events_ovrflw.write(|w| w);
+            trace!("rtc overflow");
+            self.next_period();
+        }
+
+        if self.rtc.events_compare[0].read().bits() == 1 {
+            self.rtc.events_compare[0].write(|w| w);
+            trace!("rtc compare0");
+            self.next_period();
+        }
+
+        if self.rtc.events_compare[1].read().bits() == 1 {
+            self.rtc.events_compare[1].write(|w| w);
+            trace!("rtc compare1");
+            self.trigger_alarm();
+        }
+    }
+
+    fn next_period(&self) {
+        interrupt::free(|cs| {
+            let period = self.period.fetch_add(1, Ordering::Relaxed) + 1;
+            let t = (period as u64) << 23;
+
+            let at = self.alarm.borrow(cs).get();
+
+            let diff = at - t;
+            if diff < 0xc00000 {
+                self.rtc.cc[1].write(|w| unsafe { w.bits(at as u32 & 0xFFFFFF) });
+                self.rtc.intenset.write(|w| w.compare1().set());
+            }
+        })
+    }
+
+    pub fn now(&self) -> u64 {
+        let counter = self.rtc.counter.read().bits();
+        let period = self.period.load(Ordering::Relaxed);
+        calc_now(period, counter)
+    }
+
+    fn trigger_alarm(&self) {
+        self.rtc.intenclr.write(|w| w.compare1().clear());
+        interrupt::free(|cs| self.alarm.borrow(cs).set(u64::MAX));
+
+        // TODO
+        trace!("ALARM! {:u32}", self.now() as u32);
+    }
+
+    pub fn set_alarm(&self, at: u64) {
+        interrupt::free(|cs| {
+            let t = self.now();
+            if at <= t {
+                self.trigger_alarm();
+                return;
+            }
+
+            self.alarm.borrow(cs).set(at);
+
+            let diff = at - t;
+            if diff < 0xc00000 {
+                self.rtc.cc[1].write(|w| unsafe { w.bits(at as u32 & 0xFFFFFF) });
+                self.rtc.intenset.write(|w| w.compare1().set());
+
+                // We may have been preempted for arbitrary time between checking if `at` is in the past
+                // and setting the cc. In that case, we don't know if the cc has triggered.
+                // So, we check again just in case.
+
+                let t = self.now();
+                if at <= t {
+                    self.trigger_alarm();
+                    return;
+                }
+            } else {
+                self.rtc.intenclr.write(|w| w.compare1().clear());
+            }
+        })
+    }
+
+    pub fn clear_alarm(&self) {
+        self.set_alarm(u64::MAX);
+    }
+}
+
+/// Implemented by all RTC instances.
+pub trait Instance: Deref<Target = rtc0::RegisterBlock> + Sized {
+    /// The interrupt associated with this RTC instance.
+    const INTERRUPT: Interrupt;
+
+    fn set_rtc_instance(rtc: &'static RTC<Self>);
+    fn get_rtc_instance() -> &'static RTC<Self>;
+}
+
+macro_rules! impl_instance {
+    ($name:ident, $static_name:ident) => {
+        static mut $static_name: Option<&'static RTC<$name>> = None;
+
+        impl Instance for $name {
+            const INTERRUPT: Interrupt = Interrupt::$name;
+            fn set_rtc_instance(rtc: &'static RTC<Self>) {
+                unsafe { $static_name = Some(rtc) }
+            }
+            fn get_rtc_instance() -> &'static RTC<Self> {
+                unsafe { $static_name.unwrap() }
+            }
+        }
+
+        #[interrupt]
+        fn $name() {
+            $name::get_rtc_instance().on_interrupt();
+        }
+    };
+}
+
+impl_instance!(RTC0, RTC0_INSTANCE);
+impl_instance!(RTC1, RTC1_INSTANCE);
+
+#[cfg(any(feature = "52832", feature = "52833", feature = "52840"))]
+impl_instance!(RTC2, RTC2_INSTANCE);