The flowchart in This Figure describes how to power down using the APU. As a preparation for power down, the APU program must follow these steps.
•Disable interrupts to the core.
•Record the intention to power down the CPU in the CPUPWRDWNREQ field of the PWRCTL register in APU by writing 1 to the field that corresponds to that APU core.
•Save the state of the APU core.
•Configure the GIC or GIC proxy (if the ACPU power-down is expected to be followed by the FPD power-down) for the wake source.
•Execute a waiting for interrupt (WFI) instruction.
Because the CPUPWRDWNREQ field marks the intention of the APU core to power down, the execution of the WFI instruction not only puts the APU core in a wait state, it also causes the power-down request to propagate outside the core and inform the PMU processor by asserting the GPI2 interrupt.
