The following figure shows the detailed interactions between different processors for a suspend resume use case.
Figure 1. APU Subsystem Suspend/Resume Flow
Note: PSM is not applicable for Versal AI Edge Series Gen 2 and
Versal Prime Series Gen 2 devices. All power up and power down interrupts are
directly come to PLM and PLM handles all power up down requests.
In this example, a peripheral is set up as a wake up source. Each step in the flow is explained as follows:
Suspend Flow
- APU saves the CPU context in the DDRMC.
- Peripheral is configured to be used as a wake up source.
- APU through the TF-A or XilPM client (if APU bare-metal application is running) informs PMC of its intent to suspend. PLM enables WFI interrupt.
- Informs PLM of the Wake Up Source.
- APU executes WFI instruction which triggers power down interrupt to PSM.
- PSM handshakes with PLM to initiate APU power down.
- After the handshake, PSM powers down the APU. It enables power gating, enables isolation, asserts reset and disables clock on the APU.
Wake Up Flow
- The peripheral (configured by the APU to act as a wake up source) interrupts PSM.
- PSM handshakes with PLM to initiate APU power up.
- After the handshake, PSM powers up the APU. It disables power gating, deassert reset, and disables clock gating on the APU.
- APU resumes context stored in the DDRMC.