Provided is a control method for an advanced configuration and power interface (ACPI) in a computer system. The computer system comprises a processor and a bus master, wherein the processor, as defined by the ACPI specification, has a first state (C0 state), a second state (C1 state), a third state (C2 state), a fourth state (C3 state) and a fifth state (C4 state). The method comprises enabling the processor to run in the C2 state when a request from the bus master is issued before the processor enters the C3 state, or enables the processor to ignore the C4 state and complete the C3 state when the request from the bus master is issued at the C3 state and before entering the C4 state.