Adding basic support for v7m sync primatives and mutex convenience functions.

lib/cm3/sync.c

@@ -0,0 +1,67 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2012 Fergus Noble <fergusnoble@gmail.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <libopencm3/cm3/sync.h>
+
+u32 __ldrex(volatile u32* addr)
+{
+	u32 res;
+	__asm__ volatile ("ldrex %0, [%1]" : "=r" (res) : "r" (addr));
+	return res;
+}
+
+u32 __strex(u32 val, volatile u32* addr)
+{
+	u32 res;
+	__asm__ volatile ("strex %0, %2, [%1]" :
+										"=&r" (res) : "r" (addr), "r" (val));
+	return res;
+}
+
+void __dmb()
+{
+	__asm__ volatile ("dmb");
+}
+
+void mutex_lock(mutex_t* m)
+{
+	u32 status = 0;
+
+	do {
+		/* Wait until the mutex is unlocked. */
+		while (__ldrex(m) != MUTEX_UNLOCKED);
+
+		/* Try to acquire it. */
+		status = __strex(MUTEX_LOCKED, m);
+
+	/* Did we get it? If not then try again. */
+	} while (status != 0);
+
+	/* Execute the mysterious Data Memory Barrier instruction! */
+	__dmb();
+}
+
+void mutex_unlock(mutex_t* m)
+{
+	__dmb();
+
+	/* Free the lock. */
+	*m = MUTEX_UNLOCKED;
+}
+