Chapter 4 - DSpace at Waseda University

Figure 2.3: The execution of local timer soft interruption handler
And then, there are many kinds of timers in the Linux kernel.
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Chapter 2
� RTC: Every system has a real-time clock that runs in itself regardless of any other
chips. After booting, the Linux kernel reads RTC and sets up the present time.
� TSC: The 80x86 micro-processor has a clock pin which receives signals from the
outer oscillator. Whenever the CLK pin receives the signals, the signals are saved in
the 64 bit Time Stamp Counter register.
� PIT: PIT is a counter which triggers an interrupt when it reaches the programmed
count. There are one-shot mode and periodic mode. One-shot timers interrupt only
once, and then stop counting. Periodic timers interrupt every time when they reach a
specific value.
� APIC: Local time of CPU. APIC generates an interrupt once or in a cycle such like
PIT. However APIC sends the interrupt only to its own processor.
� ACPI PMT: ACPI Power Management Timer. ACPI PMT is built in the ACPI main