10.2.5. Power Management Controller

You can only put the CPU into Dormant mode or Shutdown mode if it is integrated into a system with a memory-mapped Power Management Controller (PMXEVCNTR). The PMXEVCNTR must respond to software running on the CPU to power down the appropriate logic at the right time. The PMXEVCNTR must also respond to stimulus from the system, to power up the CPU logic and return it to Run mode.

Both Standby mode and Dormant mode are entered through Standby mode. You must program the PMXEVCNTR to indicate which mode you want to enter, then perform the appropriate state-saving operations. After this is done, execute WFI or WFE to enter Standby mode.

When the CPU is in Standby mode, nWFIPIPESTOPPEDm or nWFEPIPESTOPPEDm is asserted to indicate that the CPU pipeline has quiesced. The PMXEVCNTR must also ensure that the system provides no stimulus to the CPU so that the whole CPU is quiesced. For example, no new transactions to the Cortex-R5 AXI-slave interface can be started, and all outstanding transactions must be completed. Only when the CPU is completely quiesced can the PMXEVCNTR remove power from the logic. If the system provides stimulus, for example an interrupt to the CPU, after it has entered Standby mode, the CPU might have started to exit Standby mode when the power is removed, that can lead to corruption of the system.

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