4 Trace port triggers

The TPIU trace port is backwards compatible with non-CoreSight™ systems where a single ETM drives the trace port. Compatibility is achieved when tracectl is implemented and bypass or normal mode is selected in the Formatter and Flush Control Register, FFCR.

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. The TPIU 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 trigger can be:

The following table extends the ETMv3 specification on how a trigger is represented.

Table 4-2 CoreSight representation of triggers

tracectl tracedata Trigger Capture Description
[1] [0] Yes/No Yes/No
0 x x No Yes Normal trace data
1 0 0 Yes Yes Trigger packeta
1 1 0 Yes No Trigger
1 x 1 No No Trace disable

The trigger packet encoding is required for the ETMv3 protocol that uses a special encoding for triggers that always occur on the lower bits of tracedata.

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