Chapter 45. Pentium^® 4 CPU Arbitration

The Previous Chapter

This chapter introduced the Pentium® 4 FSB. It included:

• Enhanced Mode Scalable Bus.

• FSB Agents.

• The Request Agent.

• The Transaction Phases.

• Transaction Pipelining.

• Transaction Tracking.

This Chapter

This chapter provides a detailed description of how the processors arbitrate for ownership of the FSB. It includes:

• The Request Phase.

• Logical versus Physical Processors.

• No External Arbiter Required.

• The Rotating ID.

• The Busy/Idle Indicator.

• Requesting Ownership.

• Definition of an Arbitration Event.

The Next Chapter

This chapter provides a detailed description of how priority agents arbitrate for ownership of the FSB. It includes:

• Priority Agent Arbitration—Despotism.

• Example Priority Agents.

• Priority Agent Beats Symmetric Agents, Unless...

• Using Simple Approach, Priority Agent Suffers Penalty.

• Smarter Priority Agent Gets Ownership Faster.

• Ownership Attained in 1 BCLK.

• Ownership Attained in 2 BCLKs.

• Be Fair to the Common People.

• Priority Agent Parking.