Devices are divided into master and slave categories

devices is one that initiates actions

is one that responds to requests by a master

In a very simple system the processor is the only one allowed to be the bus master

It is good in avoiding conflict, but it needs processor to be involved in every transaction uses the bus

In system with …. master device a bus arbitration is needed

Bus arbitration

A centralized arbiter selects who gets the bus

If collision (multi requests in the same time), the device must make another request

Instead of a central authority to get the bus, the devices themselves determine who has the height priority and get the bus

Fairness is not ensured (low priority devices may be starved out –never allowed to use the bus)

Daisy chain arbitration uses a “……” control line that passed down the bus from the height priority to the lowest priority devices

uses a “grant bus” control line that passed down the bus from the height priority to the lowest priority devices

similar to centralized arbitration

Bottleneck can result

Simple but not fair