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Basic bus: Multiple Initiators.

Basic bus, but now with two initiating devices.

Needs arbitration between initiators: static priority, round robin, etc.. With multiple initiators, the bus may be busy when a new initiator wants to use it, so there are various arbitration policies that might be used. Preemptive and non-preemptive with static priority, round robin, and others mentioned above.

The maximum bus throughput of unity is now shared among initiators.

Need acknowledge signals for each request and each operation (not shown).

How long to hold bus before re-arbitration ? Commonly re-arbitrate after every burst. The latency in a non-preemptive system depends on how long the bus is held for. Maximum bus holding times affect response times for urgent and real-time requirements.


42: (C) 2008-15, DJ Greaves, University of Cambridge, Computer Laboratory.