3.13. 851871: ETM May Lose Counter Events While Entering WFx Mode
If the ETM resources become inactive because of a low-power state, there is a one-cycle window during which the counters and the sequencer may ignore counter-at-zero resources.
The following sequence is required for this erratum to occur:
- The core executes a WFI or WFE instruction.
- The ETM enters a low-power state.
- In a one-cycle window around this point, either:
- A counter in self-reload mode generates a counter-at-zero resource.
- A counter in normal mode gets a RLDEVENT on the cycle in which it has just transitioned to zero.
- A counter or sequencer is sensitive to the counter-at-zero resource.
Counters sensitive to a counter-at-zero resource may not reload or decrement. If the sequencer is sensitive to a counter-at-zero resource, it may not change state, or may change to an incorrect state.
WorkaroundThe ETM can be prevented from entering low-power mode by setting the LPOVERRIDE bit of Trace Event Control 1 (TRCEVENTCTL1R) register. This workaround is only needed if there is a counter or sequencer sensitive to a counter-at-zero resource.
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