4.4.2. Trace disabled conditions

This indicates that the current cycle must not be captured because it contains no useful data. For ETMv1.x the trace disabled conditions are:

For ETMv2.x the trace disabled conditions are:

For ETMv3.x the trace disabled conditions are:

Storage of TRACECTL

TCDs designed for ETMv3.x can discard TRACECTL after it has been used to detect trigger and trace disabled conditions, storing only TRACEDATA. This means that more efficient packing of the trace data in the TCD is possible.

Because future devices might not be able to output the trigger condition on the trace port without corrupting the trace stream, TCDs must be able to capture the trigger condition without capturing TRACEDATA. The CoreSight formatting protocol is an example where TRACEDATA must not be captured under a trigger condition. For more information, see the CoreSight Architecture Specification.

Table 4.1 shows the situations that must be recognized.

Table 4.1. Trace disabled conditions

0xxCapture TRACEDATA[n:0]
11xTrace disabled, discard TRACEDATA[n:0]
100Trigger[a], capture TRACEDATA[n:0]
101Trigger[b], discard TRACEDATA[n:0]

[a] This is how all ETMv3.x devices output a trigger.

[b] This is for future devices where the trigger is indicated on the trace port, but TRACEDATA must not be captured because this might corrupt the trace stream.

TCDs that are only designed to capture ETMv3.x trace only have to inspect TRACECTL and TRACEDATA[0] to detect the trigger condition. However, if a TCD is to be compatible with future devices, it must inspect TRACEDATA[1].

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