diff --git a/libraries/AP_HAL/Semaphores.h b/libraries/AP_HAL/Semaphores.h
index 2394d58f18..00e3e335a9 100644
--- a/libraries/AP_HAL/Semaphores.h
+++ b/libraries/AP_HAL/Semaphores.h
@@ -1,20 +1,18 @@
 
-#ifndef __AP_HAL_SEMAPHORE_H__
-#define __AP_HAL_SEMAPHORE_H__
+#ifndef __AP_HAL_SEMAPHORES_H__
+#define __AP_HAL_SEMAPHORES_H__
 
 #include <AP_HAL_Namespace.h>
 
+#include <limits.h>
+
+#define HAL_SEMAPHORE_BLOCK_FOREVER UINT32_MAX
+
 class AP_HAL::Semaphore {
 public:
-    // get - to claim ownership of the semaphore
-    virtual bool get(void* caller) = 0;
-
-    // release - to give up ownership of the semaphore
-    virtual bool release(void* caller) = 0;
-
-    // call_on_release - returns true if caller successfully added to the
-    // queue to be called back
-    virtual bool call_on_release(void* caller, AP_HAL::Proc k) = 0;
+    virtual bool take(uint32_t timeout_ms) = 0;
+    virtual bool take_nonblocking() = 0;
+    virtual bool give() = 0;
 };
 
-#endif  // __AP_HAL_SEMAPHORE_H__
+#endif  // __AP_HAL_SEMAPHORES_H__