Patent ID: 7007180

Claim:
A power saving control method for use on a computer system, comprising the steps of: checking, when there is no executable user task and therefore a CPU has entered an idle state, if any timer-expiration-waiting event is present in an event queue, which manages event-waiting tasks; switching the computer system to a first power saving operation mode when there is any timer-expiration-waiting event in the event queue, said first power saving operation mode stopping a CPU operation clock while allowing a timer interrupt to be accepted; switching the computer system to a second power saving operation mode when there is no timer-expiration-waiting event in the event queue, said second power saving operation mode inhibiting the timer interrupt while stopping the CPU operation clock; saving the time of a hardware timer when entering the second power saving operation mode; returning the computer system from the first or the second power saving operation mode to a normal operation mode in response to an occurrence of an interrupt; and detecting the time of the hardware timer when the computer system returns from the second power saving operation mode to the normal operation mode, calculating an elapsed time from the saved time, and correcting a timer value of a software timer based on the elapsed time.