When an ECAM access is performed to the primary bus number, self-configuration of the integrated block for PCIe is performed. A PCIe configuration transaction is not performed and is not presented on the link. When an ECAM access is performed to the bus number that is equal to the secondary bus value in the Enhanced PCIe Type 1 configuration header, then Type 0 configuration transactions are generated.
When an ECAM access is attempted to a bus number that is in the range defined by the secondary bus number and subordinate bus number range (not including secondary bus number), then Type 1 configuration transactions are generated. The primary, secondary and subordinate bus numbers are written and updated by Root Port software to the Type 1 PCI™ Configuration Header of the Bridge core in the enumeration procedure.
When an ECAM access is attempted to a bus number that is out of the range defined by the secondary bus_number and subordinate bus number, the bridge does not generate a configuration request and signal a SLVERR response on the AXI4 bus.
When an Unsupported Request (UR) response is received for a configuration read request, all ones are returned on the AXI4 bus to signify that a device does not exist at the requested device address. It is the responsibility of the software to ensure configuration write requests are not performed to device addresses that do not exist. However, the Bridge core asserts SLVERR response on the AXI4 bus when a configuration write request is performed on device addresses that do not exist or a UR response is received.