Does an enabled general purpose event (GPE) always have to generate a system control interrupt (SCI)?
Yes. All enabled GPEs always must generate an SCI. In addition, wake event GPEs must also wake the computer. Note that it is not adequate to only wake the computer. The operating system uses the SCI interrupt to process ACPI events signaled by GPEs, whether the system is asleep or awake when the event occurs. In other words, the wake event has the side effect of causing the system to wake up if it is asleep, but its primary purpose is to generate an SCI that notifies the operating system that the event has occurred. This is a key part of power conservation while the system is awake (that is, working). In G0 (the Working state), devices will often be placed in low-power states (D1-D3) to save energy while waiting for events. Wake-up signaling was defined because devices that are in low power states cannot communicate with the system (no interrupts or I/O or Memory accesses to the device are possible.) The operating system uses wake-up signaling to, for example, wait for a PC card insert
