Chapter 47. Pentium^® 4 Locked Transaction Series

The Previous Chapter

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

• 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.

This Chapter

This chapter describes the FSB locking mechanism, the reason for its existence, and the instructions that invoke it. It includes:

• The Shared Resource Concept.

• Testing the Availability of and Gaining Ownership of Shared Resources.

• A Race Condition Can Present a Problem.

• Guaranteeing the Atomicity of a Read/Modify/Write.

• Locking a Cache Line.

The Next Chapter

This chapter describes the mechanism that permits FSB agents to limit the number of transactions that can be injected into the FSB. It includes:

• Assert BNR# When One Entry Remains.

• BNR# Can Be Used by a Debug Tool.

• Who Monitors BNR#.

• BNR# is a Shared Signal.

• The Stalled/Throttled/Free Indicator.

• Initial Entry to the Stalled State.

• The Throttled State.

• The Free State.

• As an Agent Approaches Full, It Signals BNR# to Stall Everyone.

• BNR# Behavior at Powerup.

• BNR# Behavior During Runtime.