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Priority and daisy-chain arbitration briefly

Short answer

Arbitration decides which requester gets the bus. Priority arbtration uses a central arbiter with individual Req/Ack lines, granting the highest-priority request (fixed or roating). Daisy-chain shares one Req line; the Grant passes serially, and the first requesting device in the chain captures it, with priority set by position.

What is arbitration? Explain Priority Arbitration and Daisy Chain Arbitration in brief.

Arbitration is the process of deciding which of several devices requesting the shared system bus at the same time gets it. Only one master can use the bus at a time, so an arbiter grants access based on a rule.

Priority arbitration

  • A central priority arbiter has a separate Req/Ack pair for each device.
  • Devices assert Req; the arbiter grants Ack to the device with the highest priority among pending requests.
  • Priority can be fixed (permanent rank) or rotating (round-robin, for fairness).
 Req1,Req2,Req3 --> [Priority arbiter] --> Ack1,Ack2,Ack3
  • Merits: fast, programmable priority. Demerits: more wires, complex arbiter, starvation with fixed priority.

Daisy-chain arbitration

  • All devices share one Req line; the grant (Ack) signal passes serially through the devices.
  • A device that did not request passes the grant on; a requesting device keeps it and uses the bus. Priority is set by position (nearest to the arbiter is highest).
 Arbiter --Grant--> Dev1 --> Dev2 --> Dev3
    ^--------------- Req (common) ----------
  • Merits: simple, few wires, easy to extend. Demerits: fixed priority, slow grant propagation, chain breaks if a device fails.

✓ Answer checked by Claude Opus 5.5 (high effort)

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