RapidIO: The Next Generation Communication Fabric For Embedded Application

A.4. EXTENDED FEATURES DATA STRUCTURE

The RapidIO capability and command and status registers implement an extended capability data structure. If the extended features bit (bit 28) in the processing element features register is set, the extended features pointer is valid and points to the first entry in the extended features data structure. This pointer is an offset into the standard 16 Mbyte capability register (CAR) and command and status register (CSR) space and is accessed with a maintenance read operation in the same way as when accessing CARs and CSRs.

The extended features data structure is a singly linked list of double-word structures. Each of these contains a pointer to the next structure (EF_PTR) and an extended feature type identifier (EF_ID). The end of the list is determined when the next extended feature pointer has a value of logic 0. All pointers and extended features blocks shall index completely into the extended features space of the CSR space, and all shall be aligned to a double-word boundary so the three least significant bits shall equal logic 0. Pointer values not in extended features space or improperly aligned are illegal and shall be treated as the end of the data structure. Figure A.1 shows an example of an extentended features data structure.

Figure A.1. Example extended features data structure