Title: clck_tick()

clck_tick() is called upon receipt of a message from the synchronous alarm task in the endless loop within main(). clck_tick() simply sets next_timeout to zero (0) and then calls set_timer(), which sets clck_call_expire if a timer has expired, causing clck_expire_timers() to be called. clck_expire_timers()'s most important task is to call the client-specific timeout function (e.g., arp_timeout()) to handle the time-out. clck_expire_timer() also calls set_timer() to set another timer with the synchronous alarm task.