Why does my Hard IP for PCI Express in Root Port mode not return a Vendor ID=0xFFFFFFFF for a device that's not present?

Device Family: Intel® Arria® 10 GT, Intel® Arria® 10 GX, Intel® Arria® 10 SX, Arria® V GT, Arria® V GX, Arria® V GZ, Arria® V ST, Arria® V SX, Cyclone® V GT, Cyclone® V GX, Cyclone® V SE, Cyclone® V ST, Cyclone® V SX, Stratix® V E, Stratix® V GS, Stratix® V GT, Stratix® V GX

Type: Answers

Area: Intellectual Property

Description

This behavior is expected. If a configuration read is attempted for a device that is not present on a downstream bus (or for busses not present), the Hard IP core will return a Completion without data, showing Unsupported Request (UR).

Workaround/Fix

The driver software communicating with the Hard IP core must be aware that a configuration read of the Vendor ID register was pending and that the Completion without data and UR indicate device/bus/function not present. If this request was from higher layer software the driver should report a Vendor ID=0xFFFFFFFF to meet the expectations of system software components.

The Altera® Hard IP for PCI® Express is a root port device, it is the surrounding Root Complex that is responsible for reporting the 0xFFFFFFFF Vendor ID.