8.2. Enabling the ETM interface

The only input to the ETM interface of the ARM966E-S is an enable signal which determines whether the required ARM9E-S inputs and outputs are driven out from the ARM966E-S.

The ETM enable is controlled by the top level pin ETMEN. When this input is HIGH, the ETM interface is enabled and the outputs are driven so that an external ETM can begin code tracing.

When the ETMEN input is driven LOW, the ETM interface outputs are held at their last value before the interface was disabled. At reset, all ETM interface outputs are reset LOW.

The ETMEN input is usually driven by the ETM, and driven HIGH once the ETM has been programmed using its TAP controller.

Note

If an ETM is not used in an embedded ARM966E-S design, the ETMEN input should be tied LOW to save power.

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