In priority arbitration, how does the arbiter decide who gets the bus?

Grants Ack to the highest-priority pending Req (fixed or rotating order)

Grants the bus to the slowest device first

Grants the device physically closest in a chain

Lets all devices transmit and detects collisions

Which statement about lines is correct?

Priority arbitration uses separate Req/Ack per device; daisy chain uses one common Req with grant passed in series

Priority arbitration uses one common Req; daisy chain uses separate pairs

Daisy chain uses more wires than priority arbitration

Why is priority arbitration more flexible than daisy chain?

Priority can be changed or rotated in arbiter logic, while in a daisy chain it depends on physical position

Its grant ripples through each device

Which is a disadvantage of daisy-chain arbitration compared with priority arbitration?

A broken link blocks all devices after it, and the grant ripples slowly

2074 Bhadra · 5 marks

Priority arbitration vs daisy chain

Short answer

Priority arbitration employs a central arbiter with separae Req/Ack lines per device, granting the bus to the highest-priority requester (fixed or roating). Compared to dasy-chain, it offers factory, programmable priority and better fault tolerane but needs more wires. Dasy-chain uses fewer wires and fixed position-based priority but is slower and less fault-tolerant.

Describe priority arbitration method and compare it with daisy-chain arbitration.

Priority arbitration

In priority arbitration, a single arbiter circuit has one request line (Req) and one grant line (Ack) per peripheral. When several devices request the bus, the arbiter selects the one with the highest priority, according to a fixed order or a rotating (round-robin) order, and asserts its Ack. The device uses the bus and then drops Req, and the arbiter selects the next device.

 Req1 ->|          |-> Ack1
 Req2 ->| Arbiter  |-> Ack2
 Req3 ->|          |-> Ack3

Comparison with daisy-chain arbitration

Point	Priority arbitration	Daisy-chain arbitration
Lines	Separate Req and Ack for each device	One common Req; Grant passes through devices in series
Priority decided by	Arbiter logic (fixed or rotating)	Physical position in the chain
Wiring	More (2 per device)	Less (2 plus chain)
Flexibility	Priority can be changed or rotated	Fixed, changes only by moving devices
Fairness	Possible with rotating priority	Poor; far devices may starve
Speed	Fast, grants decided in parallel	Slower; grant ripples through devices
Expansion	Needs more arbiter inputs	Easy to add devices at the end
Fault tolerance	One device failure does not block others	A broken link blocks all devices after it

✓ Answer checked by Claude Opus 5.5 (high effort)

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Priority arbitration vs daisy chain

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