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The formatter inserts source ID signals into the data packet stream so that trace data can be re-associated with its trace source. The formatter is always active when the Trace Port Mode is active.
The formatting protocol is described in the Arm® CoreSight™ Architecture Specification v2.0. You must enable synchronization in the DWT or TPIU_PSCR to provide synchronization for the formatter.
When the formatter is enabled, if there is no data to output after a frame has been started, half-sync packets can be inserted. Distributed synchronization from the DWT or TPIU_PSCR causes synchronization which ensures that any partial frame is completed, and at least one full synchronization packet is generated.