The Unabridged Pentium 4 IA32 Processor Genealogy

Example Read From a PCI Express Device

The Read Receives the Deferred Response

Refer to Figure 52-2 on page 1279 and Figure 52-3 on page 1282 during this discussion.

Figure 52-3. Read Transaction Receives a Deferred Response

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In this example, one of the processors initiates either an IO read or a memory-mapped IO read from a register within the IEEE 1394 FireWire controller on the PCI bus. The Root Complex acts as the Response Agent for the transaction and, because it will take awhile to obtain the requested read data, it issues a Deferred response to the read transaction:

1. The read transaction request is issued in BCLK cycle ...