WinUsb_SetPowerPolicy function

The WinUsb_SetPowerPolicy function sets the power policy for a device.

Syntax


BOOL __stdcall WinUsb_SetPowerPolicy(
  _In_  WINUSB_INTERFACE_HANDLE InterfaceHandle,
  _In_  ULONG PolicyType,
  _In_  ULONG ValueLength,
  _In_  PVOID Value
);

Parameters

InterfaceHandle [in]

An opaque handle to the first (default) interface on the device, which is returned by WinUsb_Initialize.

PolicyType [in]

A value that specifies the power policy to set. The following table describes symbolic constants that are defined in winusbio.h.

Policy parameter	Description
AUTO_SUSPEND (0x81)	Specifies the auto-suspend policy type; the power policy parameter must be specified by the caller in the Value parameter. For auto-suspend, the Value parameter must point to a UCHAR variable. If Value is TRUE (nonzero), the USB stack suspends the device if the device is idle. A device is idle if there are no transfers pending, or if the only pending transfers are IN transfers to interrupt or bulk endpoints. The default value is determined by the value set in the DefaultIdleState registry setting. By default, this value is TRUE.
SUSPEND_DELAY (0x83)	Specifies the suspend-delay policy type; the power policy parameter must be specified by the caller in the Value parameter. For suspend-delay, Value must point to a ULONG variable. Value specifies the minimum amount of time, in milliseconds, that the WinUSB driver must wait post transfer before it can suspend the device. The default value is determined by the value set in the DefaultIdleTimeout registry setting. By default, this value is five seconds.

Policy parameter

Description

AUTO_SUSPEND

(0x81)

Specifies the auto-suspend policy type; the power policy parameter must be specified by the caller in the Value parameter.

For auto-suspend, the Value parameter must point to a UCHAR variable.

If Value is TRUE (nonzero), the USB stack suspends the device if the device is idle. A device is idle if there are no transfers pending, or if the only pending transfers are IN transfers to interrupt or bulk endpoints.

The default value is determined by the value set in the DefaultIdleState registry setting. By default, this value is TRUE.

SUSPEND_DELAY

(0x83)

Specifies the suspend-delay policy type; the power policy parameter must be specified by the caller in the Value parameter.

For suspend-delay, Value must point to a ULONG variable.

Value specifies the minimum amount of time, in milliseconds, that the WinUSB driver must wait post transfer before it can suspend the device.

The default value is determined by the value set in the DefaultIdleTimeout registry setting. By default, this value is five seconds.

ValueLength [in]

The size, in bytes, of the buffer at Value.

Value [in]

The new value for the power policy parameter. Datatype and value for Value depends on the type of power policy passed in PolicyType. For more information, see PolicyType.

Return value

WinUsb_SetPowerPolicy returns TRUE if the operation succeeds. Otherwise, this function returns FALSE, and the caller can retrieve the logged error by calling GetLastError.

GetLastError can return the following error code.

Return code	Description
ERROR_INVALID_HANDLE	The caller passed NULL in the InterfaceHandle parameter.
ERROR_INVALID_PARAMETER	The caller passed an invalid size for the policy parameter buffer in the ValueLength parameter.
ERROR_NOT_ENOUGH_MEMORY	Indicates that there is insufficient memory to perform the operation.

Remarks

The following list summarizes the effects of changes to power management states:

All pipe handles, interface handles, locks, and alternate settings are preserved across power management events.
Any transfers that are in progress are suspended when a device transfers to a low power state, and they are resumed when the device is restored to a working state.
The device and system must be in a working state before the client can restore a device-specific configuration. Clients can determine whether the device and system are in a working state from the WM_POWERBROADCAST message.
The client can indicate that an interface is idle by calling WinUsb_SetPowerPolicy.

Requirements