Daisy Chain Arbitration
- Arbitration procedures service all processor requests on the basis of established priorities.
- The serial priority resolving technique obtained from a daisy-chain connection of bus arbitration circuits.
- Moreover, The processors connected to the system bus assigned priority according to their position along the priority control line.
- The device closest to the priority line assigned the highest priority.
- Also, When multiple devices concurrently request the use of the bus, the device with the highest priority granted access to it.
Figure: Serial (daisy-chain) arbitration
- Figure 10.9 shows the daisy chaining connection of four arbiters.
- It assumed that each processor has its own bus arbiter logic with priority.
- The priority out (PO) of each arbiter connected to the priority in (PI) of the next lower priority arbiter.
- Generally, The PI of the highest-priority unit maintained at logic 1 value.
- The highest-priority unit in the system will always receive access to the system bus when it requests it.
- Moreover, The PO output for a particular arbiter is equal to 1 if its PI input equal to 1 and the processor associated with the arbiter logic is not requesting control of the bus.
- This is the way that priority is passed to the next unit in the chain.
- When processor requests control of the bus and the corresponding arbiter finds its Pl input equal to 1, it sets its PO output to 0.
- Lower-priority arbiters receive a 0 in PI and generate a 0 in PO.
- So, Thus the processor whose arbiter has a PI = 1 and PO = 0 is the one that given control of the system bus.
- Moreover, The busy line comes from open-collector circuits in each unit and provides a wired-OR logic connection.
- If the line is inactive, it means that no other processor is using the bus.