4.4. Cycle-accurate tracing

Cycle-accurate tracing is enabled by setting the CycleAccurate bit, bit [12], in the Main Control Register to 1. However, cycle-accurate tracing in the PFT architecture differs from cycle-accurate tracing in previous ARM trace architectures.

In the PFT architecture, the PTM generates cycle-accurate trace by including an explicit cycle count in each of the following trace packets:

In the cycle-accurate versions of these packets, the cycle count always indicates the number of cycles since the last cycle count output by the PTM:

This means that a debugger can determine:

The mechanism for cycle-accurate tracing means that, when you enable cycle-accurate tracing:

From PFTv1.1, the cycle count value in an I-Sync packet which indicates a Trace Overflow or Debug Exit is unknown and must not be relied on.

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