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PCI Host Bridge Operation, describes how the Macintosh implementation of PCI supports ordinary memory access cycles. Because some PCI cards may need to use other types of PCI cycles--I/O, configuration, interrupt acknowledge, or special cycles--the Expansion Manager includes routines that create these cycle types. These routines are described in the next sections.
All of the nonmemory access routines use the type RegEntryIDPtr to identify device nodes in the device tree, as described in Name Registry Drivers should use the RegEntryIDPtr value passed to them when they were initialized. Using the RegEntryIDPtr type lets the system software determine the target device's location in the device tree, select the appropriate PCI bus to access the device, and generate the correct cycle on that bus.