use core::ops::{Deref, DerefMut}; use core::sync::atomic::{AtomicU32, Ordering}; use core::cell::UnsafeCell; use super::asm::*; /// [Power-saving features](http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dht0008a/ch01s03s02.html) #[inline] fn wait_for_update() { wfe(); } /// [Power-saving features](http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dht0008a/ch01s03s02.html) #[inline] fn signal_update() { dsb(); sev(); } const LOCKED: u32 = 1; const UNLOCKED: u32 = 0; /// Mutex implementation for Cortex-A9 /// /// [ARM Synchronization Primitives Development Article: Implementing a mutex](http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dht0008a/ch01s03s02.html) pub struct Mutex { locked: AtomicU32, inner: UnsafeCell, } unsafe impl Sync for Mutex {} unsafe impl Send for Mutex {} impl Mutex { /// Constructor, const-fn pub const fn new(inner: T) -> Self { Mutex{ locked: AtomicU32::new(UNLOCKED), inner: UnsafeCell::new(inner), } } /// Lock the Mutex, blocks when already locked pub fn lock(&self) -> MutexGuard { while self.locked.compare_and_swap(UNLOCKED, LOCKED, Ordering::Acquire) != UNLOCKED { wait_for_update(); } dmb(); MutexGuard { mutex: self } } fn unlock(&self) { dmb(); self.locked.store(UNLOCKED, Ordering::Release); signal_update(); } } /// Returned by `Mutex.lock()`, allows access to data via /// `Deref`/`DerefMutx` pub struct MutexGuard<'a, T> { mutex: &'a Mutex, } impl<'a, T> Deref for MutexGuard<'a, T> { type Target = T; fn deref(&self) -> &T { unsafe { &*self.mutex.inner.get() } } } impl<'a, T> DerefMut for MutexGuard<'a, T> { fn deref_mut(&mut self) -> &mut T { unsafe { &mut *self.mutex.inner.get() } } } /// Automatically `Mutex.unlock()` when this reference is dropped impl<'a, T> Drop for MutexGuard<'a, T> { fn drop(&mut self) { self.mutex.unlock(); } }