RapidIO: The Next Generation Communication Fabric For Embedded Application

12.4. CONFIGURING DATA STREAMING SYSTEMS

The configuration registers for data streaming support 3 parameters:

• maximum transfer unit

• maximum reassembly contexts

• maximum PDU size

Maximum transfer unit is configured to the same value in each data streaming endpoint. Failure to align this value will result in lost data. The value is specified in 4-byte increments from 32 to 256 bytes. This value refers to the size of the payload field. It does not include the fixed overhead of the packet header format. Values other than those identified by the specification may result in unknown behaviors. There is no requirement for the end point designer to enforce certain behaviors.

Maximum reassembly contexts is used by all potential sources to discover this limit in a destination. It is not 'writeable' by other elements in the RapidIO fabric. It may be a locally configurable parameter in end point designs in circumstances where the reassembly process occurs further downstream. An example is a RapidIO to CSIX bridge. (CSIX is a standard interface for network processors defined by the Network Processor Forum.) CSIX uses a segmented interface so a bridge may not need to completely reassemble packets. That may be done by the network processor, so this parameter may need to be configured based on the device to which the bridge is connected.

Another example is a bridge to a general purpose CPU. Reassembly may occur in software and be limited by the software interface. The CPU may preprogram the maximum ...