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The Unabridged Pentium 4 IA32 Processor Genealogy by Bob Colwell, Tom Shanley

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The Stalled/Throttled/Free Indicator

Each FSB agent that is capable of initiating transactions must maintain an internal indicator referred to as the Stalled/Throttled/Free indicator.

Initial Entry to the Stalled State

Refer to Figure 48-3 on page 1193. At power-up or when reset is asserted, all initiators (i.e., Request Agents) reset the indicator to the Stalled State. All Request Agents are required to start sampling BNR# on a periodic basis starting soon after reset is removed (see “BNR# Behavior at Powerup” on page 1197) and must remain in the Stalled State until BNR# is sampled deasserted. This prevents any agent from issuing a transaction until BNR# is sampled deasserted, indicating that all agents are prepared to deal with a new transaction. ...

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