3.14. Triggering a trace run

A PTM includes a trigger event to specify an important point in a trace run. You determine the trigger condition by using the event logic to configure the event resources. See Event resources and PTM events, and Trigger Event Register, ETMTRIGGER.

The trigger event specifies the conditions that must be met to generate a trigger. When a trigger occurs:

In a CoreSight system, the trigger indication to the system is normally connected to a Cross Trigger Interface (CTI) to enable it to be routed to a trace capture device such as an Embedded Trace Buffer (ETB) or Trace Port Interface Unit (TPIU).

A simple trigger can be based on memory access address or data matches, for example the execution of an instruction from a particular address. However, a more complicated set of trigger conditions is possible, such as executing a particular instruction several times, or a particular sequence of events occurring before the trigger is asserted.

In any trace run, only a single trigger can be generated by a PTM. When the trigger has been asserted you must set the ETM Programming bit of the ETMCR to 1, and then clear it to 0, before another trigger can occur.

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