Added an idle function for long running functions to call.

src/main.c

@@ -114,4 +114,9 @@ void main()
     /* ...and leave this loop in. There is an endless loop in
     *  'start.asm' also, if you accidentally delete this next line */
     for (;;);
+}
+
+void idle()
+{
+	__asm__ __volatile__ ("hlt");
 }