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11.4 Timer Interrupt Service Routines

Part of the timer chip initialization involves installing an interrupt service routine (ISR) that is called when the timer interrupt occurs. Typically, the ISR performs these duties:

The announce_time_tick function is invoked in the context of the ISR; therefore, all of the restrictions placed on an ISR are applicable to announce_time_tick. In reality, announce_time_tick is part of the timer ISR. The announce_time_tick function is called to notify the kernel scheduler about the occurrence of a timer tick. Equally important is the announcement of the timer tick to the soft-timer handling facility. These concepts are illustrated in Figure 11.3.

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Figure 11.3: Steps in servicing the timer interrupt.

The soft-timer handling facility is responsible for maintaining the soft timers at each timer tick.


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