1 files changed, 70 insertions, 0 deletions
diff --git a/examples/preemption.rs b/examples/preemption.rs
new file mode 100644
index 00000000..2ca6f951
--- /dev/null
+++ b/examples/preemption.rs
@@ -0,0 +1,70 @@
+//! Two tasks running at different priorities with access to the same resource
+
+#![deny(unsafe_code)]
+#![feature(const_fn)]
+#![feature(proc_macro)]
+#![no_std]
+
+#[macro_use(task)]
+extern crate cortex_m_rtfm as rtfm;
+extern crate stm32f103xx;
+
+use rtfm::{app, Resource, Threshold};
+
+app! {
+    device: stm32f103xx,
+
+    resources: {
+        static COUNTER: u64 = 0;
+    },
+
+    tasks: {
+        // the task `SYS_TICK` has higher priority than `TIM2`
+        SYS_TICK: {
+            priority: 2,
+            resources: [COUNTER],
+        },
+
+        TIM2: {
+            enabled: true,
+            priority: 1,
+            resources: [COUNTER],
+        },
+    },
+}
+
+fn init(_p: init::Peripherals, _r: init::Resources) {
+    // ..
+}
+
+fn idle() -> ! {
+    loop {
+        rtfm::wfi();
+    }
+}
+
+task!(SYS_TICK, sys_tick);
+
+fn sys_tick(_t: &mut Threshold, r: SYS_TICK::Resources) {
+    // ..
+
+    // this task can't be preempted by `tim2` so it has direct access to the
+    // resource data
+    **r.COUNTER += 1;
+
+    // ..
+}
+
+task!(TIM2, tim2);
+
+fn tim2(t: &mut Threshold, mut r: TIM2::Resources) {
+    // ..
+
+    // as this task runs at lower priority it needs a critical section to
+    // prevent `sys_tick` from preempting it while it modifies this resource
+    // data. The critical section is required to prevent data races which can
+    // lead to data corruption or data loss
+    r.COUNTER.claim_mut(t, |counter, _t| { **counter += 1; });
+
+    // ..
+}