ARM Technical Support Knowledge Articles

Is it OK to tie off the "HRESETn" input of an HTM?

Applies to: CoreSight System Design

Answer

The AHB Trace macrocell (HTM) is a CoreSight trace source component which observes activity on an AMBA Advanced High-Performance Bus (AHB) and produces an AMBA Trace Bus (ATB) stream of trace packets indicating bus activity.

The HTM must be fully connected to all of the relevant signals of the AHB which it is tracing in order to correctly identify the bus activity.

The bus reset signal "HRESETn" is not used to reset the HTM macro. (The HTM has a separate reset.) The "HRESETn" of the bus which is being traced allows the HTM to understand when the bus has been reset and therefore produce a correct trace packet indicating this condition rather than potentially producing an incorrect trace packet and/or entering an unexpected state.

"HRESETn" is a mandatory connection for the HTM, and should not be tied off.

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