2.4.4 Using SMPEN as a power mode indicator

You can use the SMPEN output to differentiate between a retention and powerdown opportunity. However, this is not a requirement and this communication might occur because of other methods such as message passing between the core and external power controller.

If SMPEN is HIGH, the core is still in coherency with the other cores in the processor and therefore only retention is appropriate. If SMPEN is LOW it indicates the core can be powered down.
If the SMPEN is sampled LOW when the CPU Q-Channel handshake has completed the transition to retention, the core can be returned to the active state using the Q-Channel, then if CPUQACTIVE is still LOW, the power controller can start a powerdown transition of the core.
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