4.1. About the Program Flow Trace protocol

A PTM generates a program flow trace stream. The PFT protocol describes the formatting of this trace stream. It is constructed of multiple packets of one or more bytes of data. Each packet consists of a single header byte followed by zero or more payload bytes. In general, the number of payload bytes in a packet is variable.

The trace data is output over the trace output interface, for export to an off-chip Trace Port Analyzer or capture in an on-chip buffer. Typically, this interface is based on the AMBA Trace Bus (ATB) standard, for connection to a CoreSight trace capture device.


Any instruction that requires tracing is presented to the PTM only when the processor commits it for execution.

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