Chapter 12
300 MIPS R4000 Microprocessor User's Manual
Moving from Master to Slave State
The System interface remains in master state unless one of the following
occurs:
• The external agent requests and is granted the System interface
(external arbitration).
• The processor issues a read request or completes the issue of a
cluster (uncompelled change to slave state).
External Arbitration
The System interface must be in slave state for the external agent to issue
an external request through the System interface. The transition from
master state to slave state is arbitrated by the processor using the System
interface handshake signals ExtRqst* and Release*. This transition is
described by the following procedure:
1. An external agent signals that it wishes to issue an external request by
asserting ExtRqst*.
2. When the processor is ready to accept an external request, it releases
the System interface from master to slave state by asserting Release*
for one cycle.
3. The System interface returns to master state as soon as the issue of the
external request is complete.
This process is described in External Arbitration Protocol, later in this
chapter.
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