Clock

Clock

1. hardware

   • Two modes: 1- One-shot mode (after interrupt it stops until it is explicitly started by software) 2- Square-wave mode
   • crystal oscillator
   • counter
   • holding register

2. software

   • Maintaining the time of day
     • 64 bits
     • 32 bits for seconds
     • 32 bits counter from booting
   • Preventing processes from running longer than they are allowed to
   • Accounting for CPU usage
   • Handling the alarm system call made by user processes
   • Providing watchdog timers for parts of the system itself.
     • They are frequently used to detect problems such as hangs.
   • Doing profiling, monitoring and statistics gathering