A device for PCIe might not be capable of
satisfying a specific read request. For example, if the read request targets an
unsupported address for PCIe, the completer returns a
completion TLP with a completion status of 0b001 - Unsupported
Request. The completer that returns a completion TLP with a completion
status of Reserved must be treated as an unsupported request status,
according to the PCI Express Base Specification v3.0. When the slave bridge receives an
unsupported request response, the Slave Unsupported Request (SUR) interrupt is asserted
and the DECERR response is asserted with arbitrary data on the AXI4 memory mapped bus.