7.11.1. Trigger

The trigger is indicated by outputting the trigger packet header. Figure 7.47 shows the trigger packet header.

Figure 7.47. Trigger packet

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In multi-byte ports this must be output on TRACEDATA[7:0], and Ignore packets can be inserted into the trace to ensure that this is the case.

The trigger packet is output even if the ETM is recovering from an overflow.

TRACECTL is asserted on this cycle. This enables the TPA to detect that the trigger is zero.


Bit [0] of the trigger header is always output on TRACEDATA[0].

In sub-byte ports, TRACECTL is asserted on the first cycle of the trigger packet output, and deasserted on the remaining cycles, to make sure that all cycles are captured.

In ETMv3.0, the trigger is output within a few cycles of the cycle it occurred on. In ETMv3.1 and later, the trigger is output in a cycle-accurate manner.

The trigger packet is output in the trace stream when the trigger event occurs and is unaffected by the generation of other trace packets. This means that it is output even when TraceEnable is LOW.

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