The Class Code identifies the general function of a device, and is divided into three byte-size fields. The Vivado IDE allows you to either enter the 24-bit value manually (default) by either selecting the Enter Class Code Manually checkbox or using the Class Code lookup assistant to populate the field. De-select the checkbox to enable the Class Code assistant.
• Base Class : Broadly identifies the type of function performed by the device.
• Sub-Class : More specifically identifies the device function.
• Interface : Defines a specific register-level programming interface, if any, allowing device-independent software to interface with the device.
Class code encoding can be found in the PCI-SIG ® specifications [Ref 8] .