Skip to main content

Types of bus arbitration

Short answer

Centralized arbitration uses a single arbiter: daisy chaining passes a grant signal along a chain (fixed priority, simple but slow), polling cycles through addresses (programmable priority), and independent requests give each device its own lines (fastest). Distributed arbitration has no central controller; modules place priority numbers on shared lines and the highest wins, avoiding a single point of failure.

Explain the different types of bus arbitration and compare them.

Bus arbitration is the method of deciding which of several modules requesting the bus becomes the bus master. Types:

1. Centralised arbitration (one arbiter)

  • Daisy chaining: all devices share a Bus Request line. The controller sends Bus Grant to the first device, which passes it along the chain if it does not need the bus. The device nearest the controller has the highest priority.
  • Polling: the controller sends a device address on poll lines (counter). The requesting device whose address matches takes the bus. Priority can be changed by changing the counting order.
  • Independent request: each device has its own request and grant lines. The arbiter chooses by priority logic, so it is the fastest.

2. Distributed arbitration (no central arbiter)

Each device has an arbitration number. On a request, devices place their numbers on shared lines and compare; the highest number wins.

Comparison

PointDaisy chainPollingIndependent requestDistributed
Control lines3log₂n + 22nlog₂n
SpeedSlowMediumFastMedium
PriorityFixed by positionProgrammableProgrammableBy number
Cost / complexityLowMediumHighHigh
FailureChain break affects devices after itPoller failureArbiter failureNo single point of failure
ExpandableEasyEasyHardEasy

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Computer Organization and Architecture chapter 1 questions →