The TPIU trace port is designed to be backwards compatible with non-CoreSight systems where the trace port is driven directly by a single ETM. Compatibility is achieved when tracectl is implemented and bypass or normal mode is selected in the Formatter and Flush Control Register.
The trigger is an indication to the TPA to stop trace capture. In CoreSight systems, the TPIU receives trigger events from trace sources through the cross-triggering system, and sends a trigger event over the trace out port to the TPA when it is ready for trace capture to stop.
The TPIU might signal a trigger as a result. This can be:
Directly from an event such as a pin toggle from the CTI.
A delayed event such as a pin toggle that has been delayed coming through the Trigger Counter Register.
The completion of a flush.
Table 9.3 extends the ETMv3 specification on how a trigger is represented.
|0||x||x||No||Yes||Normal trace data|
[a] The trigger packet encoding is required for the current ETMv3 protocol that uses a special encoding for triggers that always occur on the lower bits of tracedata.