From 6e0b5539fd440208edd9ec995ca35a93413843ba Mon Sep 17 00:00:00 2001
From: Determinant <ted.sybil@gmail.com>
Date: Wed, 18 Oct 2017 14:36:19 -0400
Subject: add mutex impl

---
 src/mutex.rs | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 src/mutex.rs

diff --git a/src/mutex.rs b/src/mutex.rs
new file mode 100644
index 0000000..1da3890
--- /dev/null
+++ b/src/mutex.rs
@@ -0,0 +1,61 @@
+use core::ops::{Deref, DerefMut};
+use core::cell::UnsafeCell;
+
+pub struct Mutex<T> {
+    res: UnsafeCell<T>,
+    locked: u8
+}
+
+pub struct MutexGuard<'a, T: 'a> {
+    lock: &'a Mutex<T>
+}
+
+impl<'a, T> Drop for MutexGuard<'a, T> {
+    fn drop(&mut self) {
+        unsafe {
+            asm!("ldr r2, $0
+                  mov r1, $1
+                  dmb
+                  str r1, [r2]"
+                :
+                : "m"(&self.lock.locked), "i"(0));
+        }
+    }
+}
+
+impl<'a, T> Deref for MutexGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.lock.res.get() }
+    }
+}
+
+impl<'a, T> DerefMut for MutexGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { &mut *self.lock.res.get() }
+    }
+}
+
+impl<T> Mutex<T> {
+    pub fn new(t: T) -> Mutex<T> {
+        Mutex{res: UnsafeCell::new(t), locked: 0}
+    }
+    pub fn lock(&self) -> MutexGuard<T> {
+        unsafe {
+            asm!("ldr r2, $0
+                  mov r1, $1
+                  spin_lock:
+                  ldrex r0, [r2]
+                  cmp r0, $1
+                  itt ne
+                  strexbne r0, r1, [r2]
+                  cmpne r0, #1
+                  beq spin_lock
+                  dmb"
+              :
+              : "m"(&self.locked), "i"(1)
+              : "r2", "r1", "r0");
+        }
+        MutexGuard{lock: self}
+    }
+}
-- 
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