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

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Priority Agent Arbitration

Example Priority Agents

While the physical processors are very polite to each other, the system may include one or more agents that play by different rules. They are referred to as Priority Agents. In Figure 46-1 on page 1167, whenever a PCI Express device adapter initiates a read from or write to system memory, the Root Complex must arbitrate for ownership of the FSB to initiate a snoop transaction. To do so, it uses the BPRI# signal (Bus Priority agent request; note that there is only one BPRI# signal). The Root Complex acts as the surrogate FSB Request Agent when a PCI Express device adapter requires access to system memory. BPRI# is an input to each processor's arbiter and, when asserted, it informs the processors ...

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