3 files changed, 41 insertions, 9 deletions
diff --git a/rtic-monotonics/src/lib.rs b/rtic-monotonics/src/lib.rs
index a4a1f428..6143fd0e 100644
--- a/rtic-monotonics/src/lib.rs
+++ b/rtic-monotonics/src/lib.rs
@@ -13,3 +13,13 @@ pub mod systick;
 
 #[cfg(feature = "rp2040")]
 pub mod rp2040;
+
+/// This marker is implemented on an interrupt token to enforce that the right tokens
+/// are given to the correct monotonic implementation.
+///
+/// This trait is implemented by this crate and not intended for user implementation.
+///
+/// # Safety
+///
+/// This is only safely implemented by this crate.
+pub unsafe trait InterruptToken<Periperhal> {}
diff --git a/rtic-monotonics/src/rp2040.rs b/rtic-monotonics/src/rp2040.rs
index e42c148e..6aa66ce0 100644
--- a/rtic-monotonics/src/rp2040.rs
+++ b/rtic-monotonics/src/rp2040.rs
@@ -4,19 +4,25 @@ use super::Monotonic;
 pub use super::{TimeoutError, TimerQueue};
 use core::future::Future;
 pub use fugit::ExtU64;
-use rp2040_pac::{timer, Interrupt, RESETS, TIMER};
+use rp2040_pac::{timer, Interrupt, NVIC, RESETS, TIMER};
 
 /// Timer implementing `rtic_monotonic::Monotonic` which runs at 1 MHz.
 pub struct Timer;
 
 impl Timer {
     /// Start a `Monotonic` based on RP2040's Timer.
-    pub fn start(timer: TIMER, resets: &mut RESETS) {
+    pub fn start(
+        timer: TIMER,
+        resets: &mut RESETS,
+        _interrupt_token: impl crate::InterruptToken<Self>,
+    ) {
         resets.reset.modify(|_, w| w.timer().clear_bit());
         while resets.reset_done.read().timer().bit_is_clear() {}
         timer.inte.modify(|_, w| w.alarm_0().set_bit());
 
         TIMER_QUEUE.initialize(Self {});
+
+        unsafe { NVIC::unmask(Interrupt::TIMER_IRQ_0) };
     }
 
     fn timer() -> &'static timer::RegisterBlock {
@@ -133,11 +139,17 @@ impl embedded_hal_async::delay::DelayUs for Timer {
 /// Register the Timer interrupt for the monotonic.
 #[macro_export]
 macro_rules! make_rp2040_monotonic_handler {
-    () => {
+    () => {{
         #[no_mangle]
         #[allow(non_snake_case)]
         unsafe extern "C" fn TIMER_IRQ_0() {
-            rtic_monotonics::rp2040::Timer::__tq().on_monotonic_interrupt();
+            $crate::rp2040::Timer::__tq().on_monotonic_interrupt();
         }
-    };
+
+        pub struct Rp2040Token;
+
+        unsafe impl $crate::InterruptToken<$crate::rp2040::Timer> for Rp2040Token {}
+
+        Rp2040Token
+    }};
 }
diff --git a/rtic-monotonics/src/systick.rs b/rtic-monotonics/src/systick.rs
index 691d7c76..b228e204 100644
--- a/rtic-monotonics/src/systick.rs
+++ b/rtic-monotonics/src/systick.rs
@@ -36,7 +36,11 @@ impl Systick {
     /// `sysclk` and `TIMER_HZ`.
     ///
     /// Note: Give the return value to `TimerQueue::initialize()` to initialize the timer queue.
-    pub fn start(mut systick: cortex_m::peripheral::SYST, sysclk: u32) {
+    pub fn start(
+        mut systick: cortex_m::peripheral::SYST,
+        sysclk: u32,
+        _interrupt_token: impl crate::InterruptToken<Self>,
+    ) {
         // + TIMER_HZ / 2 provides round to nearest instead of round to 0.
         // - 1 as the counter range is inclusive [0, reload]
         let reload = (sysclk + TIMER_HZ / 2) / TIMER_HZ - 1;
@@ -153,11 +157,17 @@ impl embedded_hal_async::delay::DelayUs for Systick {
 /// Register the Systick interrupt for the monotonic.
 #[macro_export]
 macro_rules! make_systick_handler {
-    () => {
+    () => {{
         #[no_mangle]
         #[allow(non_snake_case)]
         unsafe extern "C" fn SysTick() {
-            rtic_monotonics::systick::Systick::__tq().on_monotonic_interrupt();
+            $crate::systick::Systick::__tq().on_monotonic_interrupt();
         }
-    };
+
+        pub struct SystickToken;
+
+        unsafe impl $crate::InterruptToken<$crate::systick::Systick> for SystickToken {}
+
+        SystickToken
+    }};
 }