Events and Task Priority Levels
Events are another type of object that is managed through EFI services. An event can be created and destroyed, and an event can be either in the waiting state or the signaled state. An EFI image can do any of the following:
- Create an event.
- Destroy an event.
- Check to see if an event is in the signaled state.
- Wait for an event to be in the signaled state.
- Request that an event be moved from the waiting state to the signaled state.
Because EFI does not support interrupts, it can present a challenge to driver writers who are accustomed to an interrupt-driven driver model. Instead, EFI supports polled drivers. The most common use of events by an EFI driver is the use of timer events that allow drivers to periodically poll a device. Table 2 shows the different types of events that are supported in EFI and the relationships between those events.