Add a CPU cycle triggered callback

def add_sync_callback(self, callback_cycles, callback):
        """ Add a CPU cycle triggered callback """
        self.sync_callbacks_cyles[callback] = 0
        self.sync_callbacks.append([callback_cycles, callback])
        if self.quickest_sync_callback_cycles is None or \
                        self.quickest_sync_callback_cycles > callback_cycles:
            self.quickest_sync_callback_cycles = callback_cycles