Hot Plug Events, when implemented, are reported through either the event-scan RTAS call or a hotplug interrupt. An OS that wants to be notified of hotplug events will need to set the appropriate arch-vector bit. Look for the hot-plug-events node in the /event-sources node of the OF device tree (see ), enable the interrupts listed in its “interrupts” property and provide an interrupt handler to call check-exception when one of those interrupts are received. When a hotplug event occurs, whether reported by check-exception or event-scan, RTAS will directly pass back the Hotplug Event Log as described in . R1--1. If FRUs can be hot plugged in the system without OS support, the Hot Plug Event mechanism must be provided for signaling the OS about the event.