A PCI Express function may optionally implement any, all, or none of the following Extended Capability register sets:
Advanced Error Reporting Capability register set.
Virtual Channel (VC) Capability register set.
Device Serial Number Capability register set.
Power Budgeting Capability register set.
Refer to Figure 24-1 on page 895. The first extended capability register set must be implemented at offset 100h in a function's 4KB configuration space and its Enhanced Capability Header register (see Figure 24-15 on page 930) contains a pointer (the Next Capability Offset field; this 12-bit field must contain either the dword-aligned start address of the next capability register set, or a value of zero if this ...