2.8. Hardware event tracing

The STM hardware event observation interface enables monitoring and tracing of 32 rising-edge hardware events, each of which is represented by a single bit. You can use this functionality to monitor interrupts, cross-triggers, and other signals of interest in your system. If a hardware event is asserted and is enabled, it is captured and traced as a data packet.

To enable the STM to monitor and trace cross-trigger events in the system, ARM recommends that you connect at least two trigger outputs from a CTI to hardware event inputs on the STM. ARM recommends you also connect the inverse of these CTI trigger outputs to the hardware event inputs on the STM to enable falling edges of these signals to be traced.

Triggers can be enabled for hardware events. If triggering is enabled for a hardware event, its assertion, when captured, also causes a trigger event.

Multiple different hardware events can be merged into a single traced event.

If the same hardware event is asserted multiple times while the first captured assertion is pending and has not yet been traced, only one assertion is traced and the others are dropped. If error detection is enabled, an MERR packet is generated to indicate that merging has occurred.

See the System Trace Macrocell Programmers’ Model Architecture Specification for more information on hardware events.

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