3.17. Power-down support

The PFT architecture includes power-down support for the macrocell. This support enables the entire PTM state of the macrocell to be saved before it is powered down, and restored when it is powered up again.

Note

The PTM state is held in the PTM trace registers. See PTM trace and PTM management registers.

The main features of the PTM power-down support are:

It is implementation defined whether this power-down support is included in a PTM implementation. However, you can always read the ETMOSLSR to find whether this feature is implemented.

When power down support is implemented, a Direct JTAG interface to the PTM registers is not permitted. Access to the PTM registers from an external debugger must use the ARM Debug Interface v5. For more information see the ARM Debug Interface v5 Architecture Specification.

In a system that supports multiple power domains, the PTM might be split into two domains:

This power domain split enables the processor and core domain of the PTM to be dynamically powered down while permitting a debugger to maintain communication with the PTM, and to determine the part of the PTM that is powered down.

Typically, the PTM core power domain is the same power domain as the processor. However, some implementations might separate the PTM core power domain from the processor power domain to enable the PTM core power domain to be powered down when the PTM is not in use.

In a typical CoreSight system, the PTM Debug domain is the same power domain as the other debug and trace components. This permits an implementation to power down all the debug and trace logic when not in use.

Table 3.81 shows how the ETMOSLSR indicates the power down support that is implemented.

Table 3.81. Determining the level of power down support

PFT ArchitectureETMOSLSR[3]ETMOSLSR[0]Power down support
PFTv1.000SinglePower, see SinglePower in PFTv1.0
PFTv1.001Full Support, see Full Power Down Support in PFTv1.0
PFTv1.1 and later00SinglePower, see SinglePower from PFTv1.1
PFTv1.1 and later10Full Support, see Full Power Down Support from PFTv1.1

Values not shown are Reserved.

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