Windows Kernel Power Management API Reference

This section provides detailed documentation for the Windows Kernel Power Management APIs. These APIs allow drivers and system components to interact with the system's power management framework, enabling efficient energy usage and responsiveness.

Key Concepts

• Power States: Understanding system and device power states (S0, S1, S2, S3, S4, S5, D0, D1, D2, D3).
• Power IRPs: How the power management framework communicates power events to drivers via I/O Request Packets (IRPs).
• Device Power Management: Techniques for managing the power state of individual devices.
• System Power Management: Mechanisms for controlling the overall system power state.

Core Functions and Structures

Driver-Level Power Management

Drivers typically handle power management through IRP_MJ_POWER requests. The framework dispatches these requests to the driver's dispatch routine.

Function/Structure	Description
PoCallDriver	Allows a driver to send a power IRP to the next-lower driver in the stack.
PoStartNextPowerIrp	Notifies the power manager that a driver has completed processing a power IRP and is ready for the next one.
PoRegisterDeviceForIdleDetection	Registers a device with the system for idle detection, allowing it to enter low-power states when inactive.
PoSetPowerState	Informs the power manager of a device's new power state.
PoSetRundownPowerState	Sets the device's power state for the rundown operation.

System-Level Power Management

These functions are primarily used by system components to control system power policy and manage wake events.

Function/Structure	Description
PoRequestPowerIrp	Requests a power IRP to be sent to a specified device.
PoSetSystemState	Sets the system's power state. Deprecated in favor of PoSetSystemPowerState.
PoSetSystemPowerState	Sets the system's power state (e.g., S1, S3, S5).
PoCreateThermalZone	Creates a thermal zone object used for managing device temperature.
PoRegisterThermalZone	Registers a driver-created thermal zone with the system.

Key IRP Structures

Example Snippets

Handling IRP_MN_SET_POWER

NTSTATUS MyPowerDispatch(PDEVICE_OBJECT DeviceObject, PIRP Irp) {
    PIO_STACK_LOCATION irpSp;
    NTSTATUS status;

    irpSp = IoGetCurrentIrpStackLocation(Irp);

    switch (irpSp->MinorFunction) {
        case IRP_MN_SET_POWER:
            // Handle power state change requests
            status = HandleSetPower(DeviceObject, Irp, irpSp);
            break;
        case IRP_MN_QUERY_POWER:
            // Handle power state query requests
            status = HandleQueryPower(DeviceObject, Irp, irpSp);
            break;
        // ... other minor functions
        default:
            status = STATUS_INVALID_DEVICE_REQUEST;
            break;
    }

    return status;
}