Bus Arbitration refers to the process by which the current bus master accesses and then leaves the control of the bus and passes it to another bus requesting processor unit. The controller that has access to a bus at an instance is known as a Bus master.
A conflict may arise if the number of DMA controllers or other controllers or processors try to access the common bus at the same time, but access can be given to only one of those. Only one processor or controller can be Bus master at the same point in time. To resolve these conflicts, the Bus Arbitration procedure is implemented to coordinate the activities of all devices requesting memory transfers. The selection of the bus master must take into account the needs of various devices by establishing a priority system for gaining access to the bus. The Bus Arbiter decides who would become the current bus master.
There are two approaches to bus arbitration:
Centralized bus arbitration –
A single bus arbiter performs the required arbitration.
Distributed bus arbitration –
All devices participating in the selection of the next bus master.
Methods of Centralized BUS Arbitration –
There are three bus arbitration methods:
(i) Daisy Chaining method –
(ii) Polling or Rotating Priority method – (iii) Fixed priority or Independent Request method
