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Device Power Management


Device power management (PM) on Zephyr is a feature that enables devices to save energy when they are not being used. This feature can be enabled by setting CONFIG_PM_DEVICE to y. When this option is selected, device drivers implementing power management will be able to take advantage of the device power management subsystem.

Zephyr supports two methods of device power management:

Device Runtime Power Management

Device runtime power management involves coordinated interaction between device drivers, subsystems, and applications. While device drivers play a crucial role in directly controlling the power state of devices, the decision to suspend or resume a device can also be influenced by higher layers of the software stack.

Each layer—device drivers, subsystems, and applications—can operate independently without needing to know about the specifics of the other layers because the subsystem uses reference count to check when it needs to suspend or resume a device.

  • Device drivers are responsible for managing the power state of devices. They interact directly with the hardware to put devices into low-power states (suspend) when they are not in use, and bring them back (resume) when needed. Drivers should use the device runtime power management APIs provided by Zephyr to control the power state of devices.

  • Subsystems, such as sensors, file systems, and network, can also influence device power management. Subsystems may have better knowledge about the overall system state and workload, allowing them to make informed decisions about when to suspend or resume devices. For example, a networking subsystem may decide to keep a network interface powered on if it expects network activity in the near future.

  • Applications running on Zephyr can impact device power management as well. An application may have specific requirements regarding device usage and power consumption. For example, an application that streams data over a network may need to keep the network interface powered on continuously.

Coordination between device drivers, subsystems, and applications is key to efficient device power management. For example, a device driver may not know that a subsystem will perform a series of sequential operations that require a device to remain powered on. In such cases, the subsystem can use device runtime power management to ensure that the device remains in an active state until the operations are complete.

When using this Device Runtime Power Management, the System Power Management subsystem is able to change power states quickly because it does not need to spend time suspending and resuming devices that are runtime enabled.

For more information, see Device Runtime Power Management.

System-Managed Device Power Management

When using this method, device power management is mostly done inside pm_system_suspend() along with entering a CPU or SOC power state.

If a decision to enter a CPU lower power state is made, the power management subsystem will suspend devices before changing state. The subsystem takes care of suspending devices following their initialization order, ensuring that possible dependencies between them are satisfied. As soon as the CPU wakes up from a sleep state, devices are resumed in the opposite order that they were suspended.


When using System Power Management, device transitions can be run from the idle thread. As functions in this context cannot block, transitions that intend to use blocking APIs must check whether they can do so with k_can_yield().

This method of device power management can be useful in the following scenarios:

  • Systems with no device requiring any blocking operations when suspending and resuming. This implementation is reasonably simpler than device runtime power management.

  • For devices that can not make any power management decision and have to be always active. For example a firmware using Zephyr that is controlled by an external entity (e.g Host CPU). In this scenario, some devices have to be always active and should be suspended together with the SoC when requested by this external entity.

It is important to emphasize that this method has drawbacks (see above) and Device Runtime Power Management is the preferred method for implementing device power management.


When using this method of device power management, the CPU will not enter a low-power state if a device cannot be suspended. For example, if a device returns an error such as -EBUSY in response to the PM_DEVICE_ACTION_SUSPEND action, indicating it is in the middle of a transaction that cannot be interrupted. Another condition that prevents the CPU from entering a low-power state is if the option CONFIG_PM_NEED_ALL_DEVICES_IDLE is set and a device is marked as busy.


This method of device power management is disabled when CONFIG_PM_DEVICE_RUNTIME_EXCLUSIVE is set to y (that is the default value when CONFIG_PM_DEVICE_RUNTIME is enabled)


Devices are suspended only when the last active core is entering a low power state and devices are resumed by the first core that becomes active.

Device Power Management States

The power management subsystem defines device states in pm_device_state. This method is used to track power states of a particular device. It is important to emphasize that, although the state is tracked by the subsystem, it is the responsibility of each device driver to handle device actions(pm_device_action) which change device state.

Each pm_device_action have a direct an unambiguous relationship with a pm_device_state.


Device actions x states

As mentioned above, device drivers do not directly change between these states. This is entirely done by the power management subsystem. Instead, drivers are responsible for implementing any hardware-specific tasks needed to handle state changes.

Device Model with Power Management Support

Drivers initialize devices using macros. See Device Driver Model for details on how these macros are used. A driver which implements device power management support must provide these macros with arguments that describe its power management implementation.

Use PM_DEVICE_DEFINE or PM_DEVICE_DT_DEFINE to define the power management resources required by a driver. These macros allocate the driver-specific state which is required by the power management subsystem.

Drivers can use PM_DEVICE_GET or PM_DEVICE_DT_GET to get a pointer to this state. These pointers should be passed to DEVICE_DEFINE or DEVICE_DT_DEFINE to initialize the power management field in each device.

Here is some example code showing how to implement device power management support in a device driver.

#define DT_DRV_COMPAT dummy_device

static int dummy_driver_pm_action(const struct device *dev,
                                  enum pm_device_action action)
    switch (action) {
        /* suspend the device */
        /* resume the device */
         * powered on the device, used when the power
         * domain this device belongs is resumed.
         * power off the device, used when the power
         * domain this device belongs is suspended.
        return -ENOTSUP;

    return 0;

PM_DEVICE_DT_INST_DEFINE(0, dummy_driver_pm_action);

DEVICE_DT_INST_DEFINE(0, &dummy_init,

Shell Commands

Power management actions can be triggered from shell commands for testing purposes. To do that, enable the CONFIG_PM_DEVICE_SHELL option and issue a pm command on a device from the shell, for example:

uart:~$ device list
- buttons (active)
uart:~$ pm suspend buttons
uart:~$ device list
- buttons (suspended)

To print the power management state of a device, enable CONFIG_DEVICE_SHELL and use the device list command, for example:

uart:~$ device list
- i2c@40003000 (active)
- buttons (active, usage=1)
- leds (READY)

In this case, leds does not support PM, i2c supports PM with manual suspend and resume actions and it’s currently active, buttons supports runtime PM and it’s currently active with one user.

Busy Status Indication

When the system is idle and the SoC is going to sleep, the power management subsystem can suspend devices, as described in System-Managed Device Power Management. This can cause device hardware to lose some states. Suspending a device which is in the middle of a hardware transaction, such as writing to a flash memory, may lead to undefined behavior or inconsistent states. This API guards such transactions by indicating to the kernel that the device is in the middle of an operation and should not be suspended.

When pm_device_busy_set() is called, the device is marked as busy and the system will not do power management on it. After the device is no longer doing an operation and can be suspended, it should call pm_device_busy_clear().

Wakeup capability

Some devices are capable of waking the system up from a sleep state. When a device has such capability, applications can enable or disable this feature on a device dynamically using pm_device_wakeup_enable().

This property can be set on device declaring the property wakeup-source in the device node in devicetree. For example, this devicetree fragment sets the gpio0 device as a “wakeup” source:

gpio0: gpio@40022000 {
        compatible = "ti,cc13xx-cc26xx-gpio";
        reg = <0x40022000 0x400>;
        interrupts = <0 0>;
        status = "disabled";
        label = "GPIO_0";
        #gpio-cells = <2>;

By default, “wakeup” capable devices do not have this functionality enabled during the device initialization. Applications can enable this functionality later calling pm_device_wakeup_enable().


This property is only used by the system power management to identify devices that should not be suspended. It is responsibility of driver or the application to do any additional configuration required by the device to support it.


Some helpful examples showing device power management features: