Merge #721

721: Added nRF monotonics r=perlindgren a=korken89

Testing completed

Co-authored-by: Emil Fresk <emil.fresk@gmail.com>

8 files changed, 641 insertions, 3 deletions

diff --git a/rtic-monotonics/CHANGELOG.md b/rtic-monotonics/CHANGELOG.md
index 816bc24..2a08694 100644
--- a/rtic-monotonics/CHANGELOG.md
+++ b/rtic-monotonics/CHANGELOG.md
@@ -9,6 +9,7 @@ For each category, *Added*, *Changed*, *Fixed* add new entries at the top!
 
 ### Added
 
+- nRF52xxx, nRF9160, nRF5340 Timer and RTC monotonics
 - Interrupt tokens for `Systick` and `rp2040` to make sure an interrupt handler exists
 
 ### Changed
diff --git a/rtic-monotonics/Cargo.toml b/rtic-monotonics/Cargo.toml
index c961c05..728e171 100644
--- a/rtic-monotonics/Cargo.toml
+++ b/rtic-monotonics/Cargo.toml
@@ -23,8 +23,21 @@ fugit = { version = "0.3.6" }
 atomic-polyfill = "1"
 cfg-if = "1.0.0"
 cortex-m = { version = "0.7.6", optional = true }
+critical-section = { version = "1", optional = true }
+
+# RP2040
 rp2040-pac = { version = ">=0.2.0,<0.5", optional = true }
 
+# nRF52
+nrf52810-pac = { version = "0.12.2", optional = true }
+nrf52811-pac = { version = "0.12.2", optional = true }
+nrf52832-pac = { version = "0.12.2", optional = true }
+nrf52833-pac = { version = "0.12.2", optional = true }
+nrf52840-pac = { version = "0.12.2", optional = true }
+nrf5340-app-pac = { version = "0.12.2", optional = true }
+nrf5340-net-pac = { version = "0.12.2", optional = true }
+nrf9160-pac = { version = "0.12.2", optional = true }
+
 [features]
 default = []
 defmt = ["fugit/defmt"]
@@ -35,4 +48,14 @@ systick-100hz = []
 systick-10khz = []
 
 # Timer peripheral on the RP2040
-rp2040 = ["dep:rp2040-pac"]
+rp2040 = ["dep:cortex-m", "dep:rp2040-pac"]
+
+# nRF Timers and RTC
+nrf52810 = ["dep:cortex-m", "dep:nrf52810-pac", "dep:critical-section"]
+nrf52811 = ["dep:cortex-m", "dep:nrf52811-pac", "dep:critical-section"]
+nrf52832 = ["dep:cortex-m", "dep:nrf52832-pac", "dep:critical-section"]
+nrf52833 = ["dep:cortex-m", "dep:nrf52833-pac", "dep:critical-section"]
+nrf52840 = ["dep:cortex-m", "dep:nrf52840-pac", "dep:critical-section"]
+nrf5340-app = ["dep:cortex-m", "dep:nrf5340-app-pac", "dep:critical-section"]
+nrf5340-net = ["dep:cortex-m", "dep:nrf5340-net-pac", "dep:critical-section"]
+nrf9160 = ["dep:cortex-m", "dep:nrf9160-pac", "dep:critical-section"]
diff --git a/rtic-monotonics/src/lib.rs b/rtic-monotonics/src/lib.rs
index 6143fd0..04ce4e2 100644
--- a/rtic-monotonics/src/lib.rs
+++ b/rtic-monotonics/src/lib.rs
@@ -14,6 +14,54 @@ pub mod systick;
 #[cfg(feature = "rp2040")]
 pub mod rp2040;
 
+#[cfg(any(
+    feature = "nrf52810",
+    feature = "nrf52811",
+    feature = "nrf52832",
+    feature = "nrf52833",
+    feature = "nrf52840",
+    feature = "nrf5340-app",
+    feature = "nrf5340-net",
+    feature = "nrf9160",
+))]
+pub mod nrf;
+
+#[allow(dead_code)]
+pub(crate) const fn cortex_logical2hw(logical: u8, nvic_prio_bits: u8) -> u8 {
+    ((1 << nvic_prio_bits) - logical) << (8 - nvic_prio_bits)
+}
+
+#[cfg(any(
+    feature = "rp2040",
+    feature = "nrf52810",
+    feature = "nrf52811",
+    feature = "nrf52832",
+    feature = "nrf52833",
+    feature = "nrf52840",
+    feature = "nrf5340-app",
+    feature = "nrf5340-net",
+    feature = "nrf9160",
+))]
+pub(crate) unsafe fn set_monotonic_prio(
+    prio_bits: u8,
+    interrupt: impl cortex_m::interrupt::InterruptNumber,
+) {
+    extern "C" {
+        static RTIC_ASYNC_MAX_LOGICAL_PRIO: u8;
+    }
+
+    let max_prio = RTIC_ASYNC_MAX_LOGICAL_PRIO.max(1).min(1 << prio_bits);
+
+    let hw_prio = crate::cortex_logical2hw(max_prio, prio_bits);
+
+    // We take ownership of the entire IRQ and all settings to it, we only change settings
+    // for the IRQ we control.
+    // This will also compile-error in case the NVIC changes in size.
+    let mut nvic: cortex_m::peripheral::NVIC = core::mem::transmute(());
+
+    nvic.set_priority(interrupt, hw_prio);
+}
+
 /// This marker is implemented on an interrupt token to enforce that the right tokens
 /// are given to the correct monotonic implementation.
 ///
diff --git a/rtic-monotonics/src/nrf.rs b/rtic-monotonics/src/nrf.rs
new file mode 100644
index 0000000..0f6b973
--- /dev/null
+++ b/rtic-monotonics/src/nrf.rs
@@ -0,0 +1,4 @@
+//! Monotonic implementations for the nRF series of MCUs.
+
+pub mod rtc;
+pub mod timer;
diff --git a/rtic-monotonics/src/nrf/rtc.rs b/rtic-monotonics/src/nrf/rtc.rs
new file mode 100644
index 0000000..03610c0
--- /dev/null
+++ b/rtic-monotonics/src/nrf/rtc.rs
@@ -0,0 +1,241 @@
+//! RTIC Monotonic impl for the nRF RTCs.
+//!
+//! # Example
+//!
+//! ```
+//! use rtic_monotonics::nrf::rtc::*;
+//!
+//! fn init() {
+//!     # // This is normally provided by the selected PAC
+//!     # let rtc = unsafe { core::mem::transmute(()) };
+//!     // Generate the required token
+//!     let token = rtic_monotonics::create_nrf_rtc0_monotonic_token!();
+//!
+//!     // Start the monotonic
+//!     Rtc0::start(rtc, token);
+//! }
+//!
+//! async fn usage() {
+//!     loop {
+//!          // Use the monotonic
+//!          Rtc0::delay(100.millis()).await;
+//!     }
+//! }
+//! ```
+
+#[cfg(feature = "nrf52810")]
+use nrf52810_pac::{self as pac, Interrupt, RTC0, RTC1};
+#[cfg(feature = "nrf52811")]
+use nrf52811_pac::{self as pac, Interrupt, RTC0, RTC1};
+#[cfg(feature = "nrf52832")]
+use nrf52832_pac::{self as pac, Interrupt, RTC0, RTC1, RTC2};
+#[cfg(feature = "nrf52833")]
+use nrf52833_pac::{self as pac, Interrupt, RTC0, RTC1, RTC2};
+#[cfg(feature = "nrf52840")]
+use nrf52840_pac::{self as pac, Interrupt, RTC0, RTC1, RTC2};
+#[cfg(feature = "nrf5340-app")]
+use nrf5340_app_pac::{self as pac, Interrupt, RTC0_NS as RTC0, RTC1_NS as RTC1};
+#[cfg(feature = "nrf5340-net")]
+use nrf5340_net_pac::{self as pac, Interrupt, RTC0_NS as RTC0, RTC1_NS as RTC1};
+#[cfg(feature = "nrf9160")]
+use nrf9160_pac::{self as pac, Interrupt, RTC0_NS as RTC0, RTC1_NS as RTC1};
+
+use super::super::Monotonic;
+pub use super::super::{TimeoutError, TimerQueue};
+use atomic_polyfill::{AtomicU32, Ordering};
+use core::future::Future;
+pub use fugit::{self, ExtU64};
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __internal_create_nrf_rtc_interrupt {
+    ($mono_timer:ident, $rtc:ident, $rtc_token:ident) => {{
+        #[no_mangle]
+        #[allow(non_snake_case)]
+        unsafe extern "C" fn $rtc() {
+            $crate::nrf::rtc::$mono_timer::__tq().on_monotonic_interrupt();
+        }
+
+        pub struct $rtc_token;
+
+        unsafe impl $crate::InterruptToken<$crate::nrf::rtc::$mono_timer> for $rtc_token {}
+
+        $rtc_token
+    }};
+}
+
+/// Register the Rtc0 interrupt for the monotonic.
+#[macro_export]
+macro_rules! create_nrf_rtc0_monotonic_token {
+    () => {{
+        $crate::__internal_create_nrf_rtc_interrupt!(Rtc0, RTC0, Rtc0Token)
+    }};
+}
+
+/// Register the Rtc1 interrupt for the monotonic.
+#[macro_export]
+macro_rules! create_nrf_rtc1_monotonic_token {
+    () => {{
+        $crate::__internal_create_nrf_rtc_interrupt!(Rtc1, RTC1, Rtc1Token)
+    }};
+}
+
+/// Register the Rtc2 interrupt for the monotonic.
+#[cfg(any(feature = "nrf52832", feature = "nrf52833", feature = "nrf52840"))]
+#[macro_export]
+macro_rules! create_nrf_rtc2_monotonic_token {
+    () => {{
+        $crate::__internal_create_nrf_rtc_interrupt!(Rtc2, RTC2, Rtc2Token)
+    }};
+}
+
+macro_rules! make_rtc {
+    ($mono_name:ident, $rtc:ident, $overflow:ident, $tq:ident) => {
+        /// Monotonic timer queue implementation.
+        pub struct $mono_name;
+
+        static $overflow: AtomicU32 = AtomicU32::new(0);
+        static $tq: TimerQueue<$mono_name> = TimerQueue::new();
+
+        impl $mono_name {
+            /// Start the timer monotonic.
+            pub fn start(rtc: $rtc, _interrupt_token: impl crate::InterruptToken<Self>) {
+                unsafe { rtc.prescaler.write(|w| w.bits(0)) };
+                rtc.intenset.write(|w| w.compare0().set().ovrflw().set());
+                rtc.evtenset.write(|w| w.compare0().set().ovrflw().set());
+
+                rtc.tasks_clear.write(|w| unsafe { w.bits(1) });
+                rtc.tasks_start.write(|w| unsafe { w.bits(1) });
+
+                $tq.initialize(Self {});
+
+                // SAFETY: We take full ownership of the peripheral and interrupt vector,
+                // plus we are not using any external shared resources so we won't impact
+                // basepri/source masking based critical sections.
+                unsafe {
+                    crate::set_monotonic_prio(pac::NVIC_PRIO_BITS, Interrupt::$rtc);
+                    pac::NVIC::unmask(Interrupt::$rtc);
+                }
+            }
+
+            /// Used to access the underlying timer queue
+            #[doc(hidden)]
+            pub fn __tq() -> &'static TimerQueue<$mono_name> {
+                &$tq
+            }
+
+            /// Timeout at a specific time.
+            #[inline]
+            pub async fn timeout_at<F: Future>(
+                instant: <Self as Monotonic>::Instant,
+                future: F,
+            ) -> Result<F::Output, TimeoutError> {
+                $tq.timeout_at(instant, future).await
+            }
+
+            /// Timeout after a specific duration.
+            #[inline]
+            pub async fn timeout_after<F: Future>(
+                duration: <Self as Monotonic>::Duration,
+                future: F,
+            ) -> Result<F::Output, TimeoutError> {
+                $tq.timeout_after(duration, future).await
+            }
+
+            /// Delay for some duration of time.
+            #[inline]
+            pub async fn delay(duration: <Self as Monotonic>::Duration) {
+                $tq.delay(duration).await;
+            }
+
+            /// Delay to some specific time instant.
+            #[inline]
+            pub async fn delay_until(instant: <Self as Monotonic>::Instant) {
+                $tq.delay_until(instant).await;
+            }
+
+            #[inline(always)]
+            fn is_overflow() -> bool {
+                let rtc = unsafe { &*$rtc::PTR };
+                rtc.events_ovrflw.read().bits() == 1
+            }
+        }
+
+        #[cfg(feature = "embedded-hal-async")]
+        impl embedded_hal_async::delay::DelayUs for $mono_name {
+            type Error = core::convert::Infallible;
+
+            #[inline]
+            async fn delay_us(&mut self, us: u32) -> Result<(), Self::Error> {
+                $tq.delay((us as u64).micros()).await;
+                Ok(())
+            }
+
+            #[inline]
+            async fn delay_ms(&mut self, ms: u32) -> Result<(), Self::Error> {
+                $tq.delay((ms as u64).millis()).await;
+                Ok(())
+            }
+        }
+
+        impl Monotonic for $mono_name {
+            const ZERO: Self::Instant = Self::Instant::from_ticks(0);
+
+            type Instant = fugit::TimerInstantU64<32_768>;
+            type Duration = fugit::TimerDurationU64<32_768>;
+
+            fn now() -> Self::Instant {
+                // In a critical section to not get a race between overflow updates and reading it
+                // and the flag here.
+                critical_section::with(|_| {
+                    let rtc = unsafe { &*$rtc::PTR };
+                    let cnt = rtc.counter.read().bits() as u64;
+                    let ovf = if Self::is_overflow() {
+                        $overflow.load(Ordering::Relaxed) + 1
+                    } else {
+                        $overflow.load(Ordering::Relaxed)
+                    } as u64;
+
+                    Self::Instant::from_ticks((ovf << 24) | cnt)
+                })
+            }
+
+            fn on_interrupt() {
+                let rtc = unsafe { &*$rtc::PTR };
+                if Self::is_overflow() {
+                    $overflow.fetch_add(1, Ordering::SeqCst);
+                    rtc.events_ovrflw.write(|w| unsafe { w.bits(0) });
+                }
+            }
+
+            // NOTE: To fix errata for RTC, if the release time is within 4 ticks
+            // we release as the RTC will not generate a compare interrupt...
+            fn should_dequeue_check(release_at: Self::Instant) -> bool {
+                Self::now() + <Self as Monotonic>::Duration::from_ticks(4) >= release_at
+            }
+
+            fn enable_timer() {}
+
+            fn disable_timer() {}
+
+            fn set_compare(instant: Self::Instant) {
+                let rtc = unsafe { &*$rtc::PTR };
+                unsafe { rtc.cc[0].write(|w| w.bits(instant.ticks() as u32 & 0xffffff)) };
+            }
+
+            fn clear_compare_flag() {
+                let rtc = unsafe { &*$rtc::PTR };
+                unsafe { rtc.events_compare[0].write(|w| w.bits(0)) };
+            }
+
+            fn pend_interrupt() {
+                pac::NVIC::pend(Interrupt::$rtc);
+            }
+        }
+    };
+}
+
+make_rtc!(Rtc0, RTC0, RTC0_OVERFLOWS, RTC0_TQ);
+make_rtc!(Rtc1, RTC1, RTC1_OVERFLOWS, RTC1_TQ);
+#[cfg(any(feature = "nrf52832", feature = "nrf52833", feature = "nrf52840"))]
+make_rtc!(Rtc2, RTC2, RTC2_OVERFLOWS, RTC2_TQ);
diff --git a/rtic-monotonics/src/nrf/timer.rs b/rtic-monotonics/src/nrf/timer.rs
new file mode 100644
index 0000000..db5316f
--- /dev/null
+++ b/rtic-monotonics/src/nrf/timer.rs
@@ -0,0 +1,268 @@
+//! Monotonic impl for the 32-bit timers of the nRF series.
+//!
+//! # Example
+//!
+//! ```
+//! use rtic_monotonics::nrf::timer::*;
+//!
+//! fn init() {
+//!     # // This is normally provided by the selected PAC
+//!     # let timer = unsafe { core::mem::transmute(()) };
+//!     // Generate the required token
+//!     let token = rtic_monotonics::create_nrf_timer0_monotonic_token!();
+//!
+//!     // Start the monotonic
+//!     Timer0::start(timer, token);
+//! }
+//!
+//! async fn usage() {
+//!     loop {
+//!          // Use the monotonic
+//!          Timer0::delay(100.millis()).await;
+//!     }
+//! }
+//! ```
+
+use super::super::Monotonic;
+pub use super::super::{TimeoutError, TimerQueue};
+use atomic_polyfill::{AtomicU32, Ordering};
+use core::future::Future;
+pub use fugit::{self, ExtU64};
+
+#[cfg(feature = "nrf52810")]
+use nrf52810_pac::{self as pac, Interrupt, TIMER0, TIMER1, TIMER2};
+#[cfg(feature = "nrf52811")]
+use nrf52811_pac::{self as pac, Interrupt, TIMER0, TIMER1, TIMER2};
+#[cfg(feature = "nrf52832")]
+use nrf52832_pac::{self as pac, Interrupt, TIMER0, TIMER1, TIMER2, TIMER3, TIMER4};
+#[cfg(feature = "nrf52833")]
+use nrf52833_pac::{self as pac, Interrupt, TIMER0, TIMER1, TIMER2, TIMER3, TIMER4};
+#[cfg(feature = "nrf52840")]
+use nrf52840_pac::{self as pac, Interrupt, TIMER0, TIMER1, TIMER2, TIMER3, TIMER4};
+#[cfg(feature = "nrf5340-app")]
+use nrf5340_app_pac::{
+    self as pac, Interrupt, TIMER0_NS as TIMER0, TIMER1_NS as TIMER1, TIMER2_NS as TIMER2,
+};
+#[cfg(feature = "nrf5340-net")]
+use nrf5340_net_pac::{
+    self as pac, Interrupt, TIMER0_NS as TIMER0, TIMER1_NS as TIMER1, TIMER2_NS as TIMER2,
+};
+#[cfg(feature = "nrf9160")]
+use nrf9160_pac::{
+    self as pac, Interrupt, TIMER0_NS as TIMER0, TIMER1_NS as TIMER1, TIMER2_NS as TIMER2,
+};
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __internal_create_nrf_timer_interrupt {
+    ($mono_timer:ident, $timer:ident, $timer_token:ident) => {{
+        #[no_mangle]
+        #[allow(non_snake_case)]
+        unsafe extern "C" fn $timer() {
+            $crate::nrf::timer::$mono_timer::__tq().on_monotonic_interrupt();
+        }
+
+        pub struct $timer_token;
+
+        unsafe impl $crate::InterruptToken<$crate::nrf::timer::$mono_timer> for $timer_token {}
+
+        $timer_token
+    }};
+}
+
+/// Register the Timer0 interrupt for the monotonic.
+#[macro_export]
+macro_rules! create_nrf_timer0_monotonic_token {
+    () => {{
+        $crate::__internal_create_nrf_timer_interrupt!(Timer0, TIMER0, Timer0Token)
+    }};
+}
+
+/// Register the Timer1 interrupt for the monotonic.
+#[macro_export]
+macro_rules! create_nrf_timer1_monotonic_token {
+    () => {{
+        $crate::__internal_create_nrf_timer_interrupt!(Timer1, TIMER1, Timer1Token)
+    }};
+}
+
+/// Register the Timer2 interrupt for the monotonic.
+#[macro_export]
+macro_rules! create_nrf_timer2_monotonic_token {
+    () => {{
+        $crate::__internal_create_nrf_timer_interrupt!(Timer2, TIMER2, Timer2Token)
+    }};
+}
+
+/// Register the Timer3 interrupt for the monotonic.
+#[cfg(any(feature = "nrf52832", feature = "nrf52833", feature = "nrf52840"))]
+#[macro_export]
+macro_rules! create_nrf_timer3_monotonic_token {
+    () => {{
+        $crate::__internal_create_nrf_timer_interrupt!(Timer3, TIMER3, Timer3Token)
+    }};
+}
+
+/// Register the Timer4 interrupt for the monotonic.
+#[cfg(any(feature = "nrf52832", feature = "nrf52833", feature = "nrf52840"))]
+#[macro_export]
+macro_rules! create_nrf_timer4_monotonic_token {
+    () => {{
+        $crate::__internal_create_nrf_timer_interrupt!(Timer4, TIMER4, Timer4Token)
+    }};
+}
+
+macro_rules! make_timer {
+    ($mono_name:ident, $timer:ident, $overflow:ident, $tq:ident) => {
+        /// Monotonic timer queue implementation.
+        pub struct $mono_name;
+
+        static $overflow: AtomicU32 = AtomicU32::new(0);
+        static $tq: TimerQueue<$mono_name> = TimerQueue::new();
+
+        impl $mono_name {
+            /// Start the timer monotonic.
+            pub fn start(timer: $timer, _interrupt_token: impl crate::InterruptToken<Self>) {
+                // 1 MHz
+                timer.prescaler.write(|w| unsafe { w.prescaler().bits(4) });
+                timer.bitmode.write(|w| w.bitmode()._32bit());
+                timer
+                    .intenset
+                    .modify(|_, w| w.compare0().set().compare1().set());
+                timer.cc[1].write(|w| unsafe { w.cc().bits(0) }); // Overflow
+                timer.tasks_clear.write(|w| unsafe { w.bits(1) });
+                timer.tasks_start.write(|w| unsafe { w.bits(1) });
+
+                $tq.initialize(Self {});
+
+                timer.events_compare[0].write(|w| w);
+                timer.events_compare[1].write(|w| w);
+
+                // SAFETY: We take full ownership of the peripheral and interrupt vector,
+                // plus we are not using any external shared resources so we won't impact
+                // basepri/source masking based critical sections.
+                unsafe {
+                    crate::set_monotonic_prio(pac::NVIC_PRIO_BITS, Interrupt::$timer);
+                    pac::NVIC::unmask(Interrupt::$timer);
+                }
+            }
+
+            /// Used to access the underlying timer queue
+            #[doc(hidden)]
+            pub fn __tq() -> &'static TimerQueue<$mono_name> {
+                &$tq
+            }
+
+            /// Timeout at a specific time.
+            #[inline]
+            pub async fn timeout_at<F: Future>(
+                instant: <Self as Monotonic>::Instant,
+                future: F,
+            ) -> Result<F::Output, TimeoutError> {
+                $tq.timeout_at(instant, future).await
+            }
+
+            /// Timeout after a specific duration.
+            #[inline]
+            pub async fn timeout_after<F: Future>(
+                duration: <Self as Monotonic>::Duration,
+                future: F,
+            ) -> Result<F::Output, TimeoutError> {
+                $tq.timeout_after(duration, future).await
+            }
+
+            /// Delay for some duration of time.
+            #[inline]
+            pub async fn delay(duration: <Self as Monotonic>::Duration) {
+                $tq.delay(duration).await;
+            }
+
+            /// Delay to some specific time instant.
+            #[inline]
+            pub async fn delay_until(instant: <Self as Monotonic>::Instant) {
+                $tq.delay_until(instant).await;
+            }
+        }
+
+        #[cfg(feature = "embedded-hal-async")]
+        impl embedded_hal_async::delay::DelayUs for $mono_name {
+            type Error = core::convert::Infallible;
+
+            #[inline]
+            async fn delay_us(&mut self, us: u32) -> Result<(), Self::Error> {
+                $tq.delay((us as u64).micros()).await;
+                Ok(())
+            }
+
+            #[inline]
+            async fn delay_ms(&mut self, ms: u32) -> Result<(), Self::Error> {
+                $tq.delay((ms as u64).millis()).await;
+                Ok(())
+            }
+        }
+
+        impl Monotonic for $mono_name {
+            const ZERO: Self::Instant = Self::Instant::from_ticks(0);
+
+            type Instant = fugit::TimerInstantU64<1_000_000>;
+            type Duration = fugit::TimerDurationU64<1_000_000>;
+
+            fn now() -> Self::Instant {
+                // In a critical section to not get a race between overflow updates and reading it
+                // and the flag here.
+                critical_section::with(|_| {
+                    let timer = unsafe { &*$timer::PTR };
+                    timer.tasks_capture[2].write(|w| unsafe { w.bits(1) });
+
+                    let unhandled_overflow = if timer.events_compare[1].read().bits() & 1 != 0 {
+                        // The overflow has not been handled yet, so add an extra to the read overflow.
+                        1
+                    } else {
+                        0
+                    };
+
+                    Self::Instant::from_ticks(
+                        (unhandled_overflow + $overflow.load(Ordering::Relaxed) as u64) << 32
+                            | timer.cc[2].read().bits() as u64,
+                    )
+                })
+            }
+
+            fn on_interrupt() {
+                let timer = unsafe { &*$timer::PTR };
+
+                // If there is a compare match on channel 1, it is an overflow
+                if timer.events_compare[1].read().bits() & 1 != 0 {
+                    timer.events_compare[1].write(|w| w);
+                    $overflow.fetch_add(1, Ordering::SeqCst);
+                }
+            }
+
+            fn enable_timer() {}
+
+            fn disable_timer() {}
+
+            fn set_compare(instant: Self::Instant) {
+                let timer = unsafe { &*$timer::PTR };
+                timer.cc[0].write(|w| unsafe { w.cc().bits(instant.ticks() as u32) });
+            }
+
+            fn clear_compare_flag() {
+                let timer = unsafe { &*$timer::PTR };
+                timer.events_compare[0].write(|w| w);
+            }
+
+            fn pend_interrupt() {
+                pac::NVIC::pend(Interrupt::$timer);
+            }
+        }
+    };
+}
+
+make_timer!(Timer0, TIMER0, TIMER0_OVERFLOWS, TIMER0_TQ);
+make_timer!(Timer1, TIMER1, TIMER1_OVERFLOWS, TIMER1_TQ);
+make_timer!(Timer2, TIMER2, TIMER2_OVERFLOWS, TIMER2_TQ);
+#[cfg(any(feature = "nrf52832", feature = "nrf52833", feature = "nrf52840"))]
+make_timer!(Timer3, TIMER3, TIMER3_OVERFLOWS, TIMER3_TQ);
+#[cfg(any(feature = "nrf52832", feature = "nrf52833", feature = "nrf52840"))]
+make_timer!(Timer4, TIMER4, TIMER4_OVERFLOWS, TIMER4_TQ);
diff --git a/rtic-monotonics/src/rp2040.rs b/rtic-monotonics/src/rp2040.rs
index 9d2f4f3..c656afc 100644
--- a/rtic-monotonics/src/rp2040.rs
+++ b/rtic-monotonics/src/rp2040.rs
@@ -1,4 +1,28 @@
 //! A monotonic implementation for RP2040's Timer peripheral.
+//!
+//! # Example
+//!
+//! ```
+//! use rtic_monotonics::rp2040::*;
+//!
+//! fn init() {
+//!     # // This is normally provided by the selected PAC
+//!     # let timer = unsafe { core::mem::transmute(()) };
+//!     # let mut resets = unsafe { core::mem::transmute(()) };
+//!     // Generate the required token
+//!     let token = rtic_monotonics::create_rp2040_monotonic_token!();
+//!
+//!     // Start the monotonic
+//!     Timer::start(timer, &mut resets, token);
+//! }
+//!
+//! async fn usage() {
+//!     loop {
+//!          // Use the monotonic
+//!          Timer::delay(100.millis()).await;
+//!     }
+//! }
+//! ```
 
 use super::Monotonic;
 pub use super::{TimeoutError, TimerQueue};
@@ -22,7 +46,10 @@ impl Timer {
 
         TIMER_QUEUE.initialize(Self {});
 
-        unsafe { NVIC::unmask(Interrupt::TIMER_IRQ_0) };
+        unsafe {
+            crate::set_monotonic_prio(rp2040_pac::NVIC_PRIO_BITS, Interrupt::TIMER_IRQ_0);
+            NVIC::unmask(Interrupt::TIMER_IRQ_0);
+        }
     }
 
     fn timer() -> &'static timer::RegisterBlock {
@@ -41,6 +68,7 @@ impl Timer {
     }
 
     /// Timeout at a specific time.
+    #[inline]
     pub async fn timeout_at<F: Future>(
         instant: <Self as Monotonic>::Instant,
         future: F,
@@ -64,6 +92,7 @@ impl Timer {
     }
 
     /// Delay to some specific time instant.
+    #[inline]
     pub async fn delay_until(instant: <Self as Monotonic>::Instant) {
         TIMER_QUEUE.delay_until(instant).await;
     }
diff --git a/rtic-monotonics/src/systick.rs b/rtic-monotonics/src/systick.rs
index f4345d4..6a28a11 100644
--- a/rtic-monotonics/src/systick.rs
+++ b/rtic-monotonics/src/systick.rs
@@ -1,4 +1,28 @@
-//! ...
+//! A monotonics based on Cortex-M SysTick. Note that this implementation is inefficient as it
+//! ticks, and generates interrupts, at a constant rate.
+//!
+//! # Example
+//!
+//! ```
+//! use rtic_monotonics::systick::*;
+//!
+//! fn init() {
+//!     # // This is normally provided by the selected PAC
+//!     # let systick = unsafe { core::mem::transmute(()) };
+//!     // Generate the required token
+//!     let systick_token = rtic_monotonics::create_systick_token!();
+//!
+//!     // Start the monotonic
+//!     Systick::start(systick, 12_000_000, systick_token);
+//! }
+//!
+//! async fn usage() {
+//!     loop {
+//!          // Use the monotonic
+//!          Systick::delay(100.millis()).await;
+//!     }
+//! }
+//! ```
 
 use super::Monotonic;
 pub use super::{TimeoutError, TimerQueue};