The PCI Express Extended Capability Header Register is defined by the PCI-SIG and is used to identify the format of the extended capability and provide a pointer to the next extended capability if applicable. These fields are populated with appropriate values when the PCI Express core is generated. The following table describes the fields within the MCAP PCI Express Extended Capability Header Register. The fields and values are defined by PCI-SIG.
Bit Location | Description | Initial Value |
---|---|---|
15:0 | PCI Express Extended Capability ID - This field is a PCI-SIG defined ID number that indicates the nature and format of the Extended Capability. Extended Capability ID for the Vendor-Specific Capability is 000Bh. | 0x000B |
19:16 | Capability Version - This field is a PCI-SIG defined version number that indicates the version of the Capability structure present. Must be 0x1 for this version of the specification. | 0x1 |
31:20 | Next Capability Offset - This field contains the offset to the next PCI Express Capability structure or 000h if no other items exist in the linked list of Capabilities. For Extended Capabilities implemented in Configuration Space, this offset is relative to the beginning of PCI compatible Configuration Space and thus must always be either 0x000 (for terminating list of Capabilities) or greater than 0x0FF. | Value set automatically during IP customization |