Power management

Caution

The High-Performance Framework (HPF) support in the nRF Connect SDK is experimental and is limited to the nRF54L15 and nRF54LM20 devices.

The following page outlines the approaches and mechanisms employed to ensure efficient power management in High-Performance Framework (HPF) systems, focusing on resource allocation, system states, and interactions between different components.

Note

This page outlines best practices for architecture design. You might need to implement some components, as they are not yet available.

Power management strategies

Power Management in HPF should be considered from two perspectives: the Host controller and the HPF firmware.

Host controller

The Host is responsible for managing power state of the following resources:

  • FLPR core with HPF firmware running on it

  • RAM

To achieve optimal power state, you must use the Device Runtime Power Management and System Power Off.

See an example flow of the Host power management:

@startuml skinparam sequence { DividerBackgroundColor #8DBEFF DividerBorderColor #8DBEFF LifeLineBackgroundColor #13B6FF LifeLineBorderColor #13B6FF ParticipantBackgroundColor #13B6FF ParticipantBorderColor #13B6FF BoxBackgroundColor #C1E8FF BoxBorderColor #C1E8FF GroupBackgroundColor #8DBEFF GropuBorderColor #8DBEFF } skinparam note { BackgroundColor #ABCFFF BorderColor #2149C2 } participant Zephyr participant Application participant "HPF driver" participant "VPR driver" participant FLPR activate Zephyr Zephyr -> Zephyr : post kernel initialization activate Zephyr Zephyr -> "VPR driver" : Initialize drivers activate "VPR driver" rnote over "VPR driver" Power on FLPR RAM endrnote rnote over "VPR driver" If non-XIP: Copy code to RAM endrnote rnote over "VPR driver" Start FLPR endrnote "VPR driver" -> "VPR driver" : Initialize IPC activate "VPR driver" "VPR driver" -> FLPR activate FLPR rnote over FLPR Boot endrnote rnote over FLPR Initialize IPC endrnote return deactivate "VPR driver" "VPR driver" -> "VPR driver" : Initialize FLPR activate "VPR driver" "VPR driver" -> FLPR : FLPR_INIT activate FLPR rnote over FLPR Initialize HW, peripherals, etc endrnote return FLPR_INITD deactivate "VPR driver" return deactivate "VPR driver" deactivate Zephyr Zephyr -> Application : Start application activate Application Application -> "HPF driver" : hpf_driver_config(...) activate "HPF driver" "HPF driver" -> "HPF driver" : HPF driver initialization activate "HPF driver" "HPF driver" -> "VPR driver" : pm_device_runtime_get(&flpr) activate "VPR driver" "VPR driver" -> FLPR : FLPR_RESUME activate FLPR rnote over FLPR Enter RESUME state endrnote return FLPR_RESUMED return "HPF driver" -> FLPR : HPF_APP_CONFIGURE activate FLPR rnote over FLPR Configure HPF application endrnote return HPF_APP_CONFIGURED deactivate "HPF driver" return ... Application -> "HPF driver" : hpf_driver_transcieve(...) activate "HPF driver" "HPF driver" -> FLPR : HPF_APP_XFER activate FLPR rnote over FLPR Execute transfer endrnote return HPF_APP_XFERD return ... Application -> "HPF driver" : hpf_driver_config(...) activate "HPF driver" "HPF driver" -> "HPF driver" : HPF driver deinitialization activate "HPF driver" "HPF driver" -> FLPR : HPF_APP_DECONFIGURE activate FLPR rnote over FLPR Deconfigure HPF application endrnote return HPF_APP_DECONFIGURED "HPF driver" -> "VPR driver" : pm_device_runtime_put(&flpr) activate "VPR driver" "VPR driver" -> FLPR : FLPR_SUSPEND activate FLPR rnote over FLPR Enter SUSPENDED state endrnote return FLPR_SUSPENDED return deactivate "HPF driver" return return Zephyr -> Zephyr : power off procedure activate Zephyr "Zephyr" -> "VPR driver" : power off activate "VPR driver" "VPR driver" -> "VPR driver" : FLPR shutdown activate "VPR driver" "VPR driver" -> FLPR : FLPR_SHUTDOWN_PREPARE activate FLPR rnote over FLPR Deinitialize HW peripherals, etc endrnote return FLPR_SHUTDOWN_PREPARED deactivate "VPR driver" rnote over "VPR driver" Power off FLPR endrnote rnote over "VPR driver" Power off FLPR RAM endrnote return deactivate Zephyr @enduml

Note

VPR driver is not yet implemented, it should be implemented when writing HPF software. It shall run on application core. Its purpose is to control basic FLPR functionalities like initialization of inter processor communication and power mode management.

HPF firmware

HPF firmware is responsible for managing power states of the following resources:

  • FLPR CPU power state

  • Hardware peripherals used by the HPF firmware

FLPR CPU power state management

Your HPF firmware should not use the Zephyr libraries for System Power Management, as the libraries rely on multithreading. Instead, you must implement a distinct approach.

Your HPF firmware should configure a sleep mode that is activated using both the SLEEPSTATE and STACKONSLEEP fields in the NORDIC.VPRNORDICSLEEPCTRL register. For details, see the Sleep mode operation section in the VPR peripheral description.

This configuration must occur in the following cases:

  • When the FLPR starts (the sleep mode setting is derived from a Kconfig option).

  • When the Host receives the SUSPEND or RESUME signal.

In the main loop, the HPF firmware should call k_cpu_idle to enter sleep mode. Ensure that k_cpu_idle() is only called within the main loop to prevent the FLPR from entering an incorrect power state.

Sleep modes should be application-specific. Consider the following:

  • Latency requirements of the emulated protocol

  • Minimum time in sleep mode that brings power savings

  • Hardware limitations (for example, constraints on waking up from hibernation)

Hardware peripherals

You might have to use specific hardware peripherals with the HPF firmware.

When FLPR starts, it must initialize the required peripherals. When the Host sends a request for shutdown, these peripherals should be deinitialized and powered down before signaling that preparations for shutdown are complete.

To ensure the optimal power state of hardware peripherals, the HPF firmware should employ nrfx drivers, which are designed to manage the power states of hardware peripherals effectively.