The TPIU drives the external pins of a trace port, so that trace can be captured by an external Trace Port Analyzer (TPA). It does the following:
Inserts source ID information into the trace stream so that trace data can be re-associated with its trace source. The operation of the trace formatter is described in the ARM® CoreSight™ Architecture Specification.
Outputs patterns over the trace port so that a TPA can tune its capture logic to the trace port, maximizing the speed at which trace can be captured. For more information, see TPIU pattern generator.