The power islands are in the LPD and FPD. These are shown in the Power Diagram. The power islands are controlled by the PSM firmware. The system software writes to the PSM global registers to request power island state changes.
The system software controls the PS power-up and power-down cycles by writing to the global registers in the PSM. This is explained in the PSM Service Requests section.
For power-down requests, the PSM firmware makes the domain's interconnect transactions quiescent before a shut-down.