3 files changed, 76 insertions, 0 deletions
diff --git a/src/cs/cortex.rs b/src/cs/cortex.rs
new file mode 100644
index 0000000..cc97a12
--- /dev/null
+++ b/src/cs/cortex.rs
@@ -0,0 +1,20 @@
+use super::CriticalSection;
+
+use cortex_m::interrupt;
+
+pub struct Locker {}
+
+impl Locker {
+    pub const fn new() -> Self {
+        Self {}
+    }
+}
+
+impl CriticalSection for Locker {
+    fn with_lock<F, R>(&self, f: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        interrupt::free(|_cs| f())
+    }
+}
diff --git a/src/cs/dummy.rs b/src/cs/dummy.rs
new file mode 100644
index 0000000..86f4e90
--- /dev/null
+++ b/src/cs/dummy.rs
@@ -0,0 +1,18 @@
+use super::CriticalSection;
+
+pub struct Locker {}
+
+impl Locker {
+    pub const fn new() -> Self {
+        Self {}
+    }
+}
+
+impl CriticalSection for Locker {
+    fn with_lock<F, R>(&self, f: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        f()
+    }
+}
diff --git a/src/cs/mod.rs b/src/cs/mod.rs
new file mode 100644
index 0000000..8f97b6e
--- /dev/null
+++ b/src/cs/mod.rs
@@ -0,0 +1,38 @@
+//! Critical Section support.
+//!
+//! Types that implement the `CriticalSection` trait can be used to
+//! create critical sections to prevent data races between interrupt
+//! and non-interrupt contexts.
+//!
+//! # Note
+//!
+//! Critical sections are only acquired for updating a
+//! `HandlerTable`'s entries. They are *not* used when calling into a
+//! closure. This is because the expected implementation of critical
+//! sections turns off interrupts entirely. Given that interrupts are
+//! off, it is impossible to call an ISR, and thus no data race can
+//! occur. Additionally, because critcal sections are only enforced on
+//! updates, deadlock is impossible between updating a `HandlerTable`
+//! entry and calling into it.
+//!
+//! However, if you are going to implement your own `CriticalSection`,
+//! you need to be aware of this limitation and its rationale to avoid
+//! getting into trouble.
+
+/// Generic trait which supplies the ability to create a critical
+/// section.
+pub trait CriticalSection {
+    /// Execute `f` within a critical section.
+    fn with_lock<F, R>(&self, f: F) -> R
+    where
+        F: FnOnce() -> R;
+}
+
+#[cfg_attr(any(all(target_arch = "arm", target_os = "none")), path = "cortex.rs")]
+#[cfg_attr(
+    not(any(all(target_arch = "arm", target_os = "none"))),
+    path = "dummy.rs"
+)]
+mod csimpl;
+
+pub use csimpl::Locker;