9. Programming Model for the Avalon® -MM Root Port
The Application Layer writes TLP-formatted data for configuration read and write requests, message requests or single-dword memory read and write requests for endpoints to the Root Port TLP TX Data Registers by using the Control Register Access (CRA) interface.
Software should check the Root Port Link Status Register to ensure the Data Link Layer Link Active bit is set to 1'b1 before issuing a configuration request to downstream ports.
The TX TLP programming model can only support one outstanding non-posted request at a time, and must use tags 16 - 31 to identify non-posted requests.