3.8.3. ETM behavior when the OS Lock is set

The OS Lock is set by writing the lock key of 0xC5ACCE55 to the ETMOSLAR, see OS Lock Access Register, ETMOSLAR, ETMv3.3 and later. When the OS Lock is set all ETM functions are disabled. This means that:

You must use the WFI mechanism to ensure that the FIFO is empty before you remove power from the macrocell.


The WFI mechanism must be present on any processor and ETM combination that provides power down support. See the Technical Reference Manual (TRM) for your processor and ETM macrocell for more information.

When the OS Lock is cleared, tracing can restart. The counters, sequencer, start/stop block and Instrumentation resources continue operating from their held state. If the implementation maintains the sticky state of the address comparators during OS Lock then the address comparators continue operating with this held sticky state. However, if the ETM has been powered down since the OS Lock was set:

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