The TRG Register is reset to zero when TMCReady transitions from clear to set, that is, on entry to the Stopped or Disabled states. If the trigger count has started but not reached zero at this point, then no trigger events are observed.
The CoreSight ETB did not automatically clear the TRG Register at any time.
Tools must still reload the TRG Register between each trace capture session. Standard usage models are not affected by this change.