2.2.4. External inputs

There are five types of input resource:

Hard-wired input

External input 16 is hard-wired to provide a permanently active resource. This resource is always TRUE. It is used to permanently enable or disable events. For example, to enable tracing permanently the hard-wired input can be connected to the TraceEnable event.

FALSE is generated as the inverse of this resource, and can be used to disable an event.

External inputs

External inputs enable the ETM to respond to events outside the ETM, such as interrupts, or a trigger from another processor. They are always Imprecise.


The external inputs, EXTIN, are not related directly to memory accesses. Tracing is Imprecise if you use them in any way to enable or disable tracing. For more information about Imprecise Tracing, see Imprecise TraceEnable events.

Extended external input selectors

Extended external inputs are only defined in ETMv3.1 and later.

Extended external input selectors enable you to select inputs from a large number of extended external inputs. Figure 2.2 shows an example with four extended external inputs and two extended external input selectors.

Figure 2.2. Extended external inputs example

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Each extended external input selector is programmed to select from one of the extended external inputs, and is then available for use by any of the event blocks in the same way as any ordinary external input. An example of their use is to enable performance monitoring events to be used by the ETM.

Non-secure state resource

The Non-secure state resource enables events to be conditional on the security level.

Prohibited region resource

The prohibited region resource enables events to be disabled while trace is prohibited. This is particularly useful when using the ETM for performance monitoring, so that cycles spent in prohibited regions are not counted.

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