1. A scheduling method, comprising: in response to an occurrence of an interrupt periodically at every predetermined period, selecting one or more timers from among timers which expire at a point in time when an interrupt occurs or are already expired before the interrupt occurs, wherein each of the one or more timers represents a task, a point of time assigned to the task, a priority assigned to the task and whether a property thereof is hard or soft; determining whether the property of the selected timer is hard or soft, wherein the hard property represents that the task is non-executable or invalid after a deadline has elapsed, and the soft property represents that the task is executable and valid after the deadline has elapsed; and executing a task represented by the hard timer prior to a task represented by the soft timer and prior to a task requested by the interrupt when it is determined that the property of the selected timer is hard, and, executing the task represented by the soft timer and the task requested by the interrupt in a priority order when it is determined that the property of the selected timer is soft, and proceeding to a selecting of the task having a highest priority until all tasks represented by the hard timer are executed.