PCI-X Configuration and Initialization

This chapter illustrates that peripheral component interconnect (PCI)-X have added new requirements in terms of configuration and initialization. It describes PCI-X enhancements and modifications to configuration space and transactions. PCI-X devices need to know their device number so that they can communicate in the attribute phase of a transaction. Thus, the device number is now conveyed in type zero configuration transactions. PCI-X has made some minor changes to the 64-byte configuration header, mainly in terms of identifying characteristics that are either always present in a PCI-X device or that are not supported by PCI-X. A PCI-X capabilities list item is defined to provide expanded command and status registers and ECC data for transactions with errors. Mode 2, on the other hand expands the configuration space to 4096 bytes per function. This may be used for Extended Capabilities List items or device specific information. Both these modes are used to identify the capabilities of an add-in card at initialization time.