From a2fe6c49a8c3e86bd2bc30d9cac1d14b968bc3f5 Mon Sep 17 00:00:00 2001
From: Oliver Meier <h2obrain@gmail.com>
Date: Fri, 5 Dec 2014 16:47:52 +0100
Subject: [PATCH] [cm3/sync] Add mutex_trylock()

Allows non-blocking use in user code.
---
 include/libopencm3/cm3/sync.h |  1 +
 lib/cm3/sync.c                | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/libopencm3/cm3/sync.h b/include/libopencm3/cm3/sync.h
index e80e3485..93c12bbd 100644
--- a/include/libopencm3/cm3/sync.h
+++ b/include/libopencm3/cm3/sync.h
@@ -47,6 +47,7 @@ typedef uint32_t mutex_t;
 #define MUTEX_LOCKED	 1
 
 void mutex_lock(mutex_t *m);
+uint32_t mutex_trylock(mutex_t *m);
 void mutex_unlock(mutex_t *m);
 
 #endif
diff --git a/lib/cm3/sync.c b/lib/cm3/sync.c
index 906138ab..a9f7c99a 100644
--- a/lib/cm3/sync.c
+++ b/lib/cm3/sync.c
@@ -61,6 +61,25 @@ void mutex_lock(mutex_t *m)
 	__dmb();
 }
 
+/* returns 1 if the lock was acquired */
+uint32_t mutex_trylock(mutex_t *m)
+{
+	uint32_t status = 0;
+
+	/* If the mutex is unlocked. */
+	if (__ldrex(m) == MUTEX_UNLOCKED) {
+		/* Try to lock it. */
+		status = __strex(MUTEX_LOCKED, m);
+	}
+
+	/* Execute the mysterious Data Memory Barrier instruction! */
+	__dmb();
+
+	/* Did we get the lock? If not then try again
+	 * by calling this function once more. */
+	return status == 0;
+}
+
 void mutex_unlock(mutex_t *m)
 {
 	/* Ensure accesses to protected resource are finished */