12. System Interface
When a system event occurs, the processor issues either a single request or a series of requests--called processor requests--through the System interface, to access an external resource and service the event. For this to work, the processor System interface must be connected to an external agent that is compatible with the System interface protocol, and can coordinate access to system resources.
An external agent requesting access to processor caches or to a processor status register generates an external request. This access request passes through the System interface. System events and request cycles are shown in Figure 12-5.
Figure 12-5 Requests and System Events
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