From ff41f4dd2d082f237bcc3e9c08f408dd19f1c2c6 Mon Sep 17 00:00:00 2001 From: Astro Date: Wed, 20 Nov 2019 16:19:35 +0100 Subject: [PATCH] cortex_a9::mutex: restore and fix powersaving behaviour, doc --- src/cortex_a9/mutex.rs | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-) diff --git a/src/cortex_a9/mutex.rs b/src/cortex_a9/mutex.rs index e3fda3d..9d3c6c6 100644 --- a/src/cortex_a9/mutex.rs +++ b/src/cortex_a9/mutex.rs @@ -3,9 +3,25 @@ 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, @@ -15,15 +31,19 @@ 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 {} + while self.locked.compare_and_swap(UNLOCKED, LOCKED, Ordering::Acquire) != UNLOCKED { + wait_for_update(); + } dmb(); MutexGuard { mutex: self } } @@ -31,10 +51,13 @@ impl Mutex { fn unlock(&self) { dmb(); self.locked.store(UNLOCKED, Ordering::Release); - dsb(); + + signal_update(); } } +/// Returned by `Mutex.lock()`, allows access to data via +/// `Deref`/`DerefMutx` pub struct MutexGuard<'a, T> { mutex: &'a Mutex, } @@ -52,6 +75,7 @@ impl<'a, T> DerefMut for MutexGuard<'a, T> { } } +/// Automatically `Mutex.unlock()` when this reference is dropped impl<'a, T> Drop for MutexGuard<'a, T> { fn drop(&mut self) { self.mutex.unlock();