The option enables you to pair ETMs if you are using the Dual Core Processor hardware solution by ARM, where two ETMs output on the same traceport at the same time. It cannot be used for development platforms containing multiple ETMs that go to:

Without ETM pairing in a multiprocessor system, the Trace Port Multiplexer (TPM) might return data to the incorrect ETM in some circumstances. When you specify the correct ETM pairing, RealView Debugger handles the switching of trace data streams automatically.