+/*
+ * This is a barrier which prevents following instructions from being
+ * started until the value of the argument x is known. For example, if
+ * x is a variable loaded from memory, this prevents following
+ * instructions from being executed until the load has been performed.
+ */
+#define data_barrier(x) \
+ asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
+