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PCI Express System Architecture by MindShare, Inc, Ravi Budruk, Don Anderson, Tom Shanley

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PCI-Compatible Configuration Mechanism

For x86-based PC-AT compatible systems, the 2.3 PCI spec defines a method that utilizes processor-initiated IO accesses to instruct the host/PCI bridge (in this case, within the Root Complex) to perform PCI configuration accesses.The spec does not define a configuration mechanism to be used in systems other than PC-AT compatible systems.

Background

The x86 processor family is capable of addressing up to, but no more than, 64KB of IO address space. In the EISA spec, the usage of this IO space was defined in such a manner that the only IO address ranges available for the implementation of the PCI Configuration Mechanism (without conflicting with an ISA or EISA device) were 0400h - 04FFh, 0800h - 08FFh, and ...

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