Add mutex class.

1 files changed, 42 insertions, 0 deletions

diff --git a/mutex.h b/mutex.h
new file mode 100644
index 0000000..d12331d
--- /dev/null
+++ b/mutex.h
@@ -0,0 +1,42 @@
+#ifndef MUTEX_H
+#define MUTEX_H
+
+class Mutex {
+	private:
+		uint8_t locked;
+	public:
+		Mutex() : locked(0) {}
+		Mutex(uint8_t l) : locked(l) {}
+		
+		bool trylock() {
+			uint8_t val;
+			
+			// Check if mutex is locked.
+			asm volatile ("ldrexb %0, [%1]" : "=r" (val) : "r" (&locked));
+			if(val) {
+				return false;
+			}
+			
+			// Try taking the lock.
+			asm volatile ("strexb %0, %1, [%2]" : "=r" (val) : "r" (1), "r" (&locked));
+			if(val) {
+				return false;
+			}
+			
+			asm volatile("dmb");
+			return true;
+		}
+		
+		void lock() {
+			while(!trylock()) {
+				Thread::yield();
+			}
+		}
+		
+		void unlock() {
+			asm volatile("dmb");
+			locked = 0;
+		}
+};
+
+#endif