Using an Interrupt to Wake a Device

When a device transitions to a low-power state, the framework disconnects (or reports as inactive) interrupts that are used for I/O handling. Starting with KMDF 1.13 and UMDF 2.0 running on Windows 8.1, a WDF driver can create a framework interrupt object that remains active when the device transitions to a low-power state, and can then be used to awaken the device and restore it to its fully on D0 state.

If you are developing a WDF driver for a System on a Chip (SoC) platform, you can use such an interrupt to awaken a device that does not provide a traditional wake signaling mechanism. To use this functionality, the device must have hardware support for wake interrupts, as exposed through ACPI. The driver that creates the interrupt must be the device's power policy owner.

When the device transitions to a low-power state, the framework does not disconnect an interrupt that has been identified as wake-capable. When the device interrupts, the framework calls the driver's EvtDeviceD0Entry and EvtInterruptIsr callback routines at IRQL = PASSIVE_LEVEL.

If your driver already creates a passive-level interrupt object for I/O handling, we recommend sharing that same interrupt object for wake functionality. In this scenario, the driver's EvtInterruptIsr callback routine implements conditional logic to perform handling for I/O-related interrupts, as well as wake handling.

However, if your driver uses an interrupt that requires handling at the device's IRQL (DIRQL), we recommend creating an additional framework interrupt object to provide wake functionality.

Follow these steps to create a wake-capable interrupt object in your KMDF or UMDF driver:

  1. Call WdfDeviceAssignS0IdleSettings, typically from EvtDriverDeviceAdd, specifying IdleCanWakeFromS0 in the IdleCaps parameter.
  2. Optionally, call WdfDeviceInitSetPowerPolicyEventCallbacks to register event callback functions described in Supporting System Wake-Up.
  3. Call WDF_INTERRUPT_CONFIG_INIT to initialize a WDF_INTERRUPT_CONFIG structure. Provide an EvtInterruptIsr callback function, to be called at passive level. In the configuration structure, set PassiveHandling and CanWakeDevice to TRUE. Then call WdfInterruptCreate from your driver's EvtDevicePrepareHardware callback function to create the framework interrupt object.
  4. Call WdfDeviceAssignSxWakeSettings to configure the device to wake the system from a low-power state.
    
    WDF_DEVICE_POWER_POLICY_WAKE_SETTINGS_INIT(&wakeSettings);
    wakeSettings.DxState = PowerDeviceD3;
    wakeSettings.UserControlOfWakeSettings = WakeDoNotAllowUserControl;
    wakeSettings.Enabled = WdfTrue;
    
    status = WdfDeviceAssignSxWakeSettings(Device, &wakeSettings);
    if (!NT_SUCCESS(status)) {
        Trace(TRACE_LEVEL_ERROR,"WdfDeviceAssignSxWakeSettings failed %x\n", status);
        return status;
    }
    
    
    
  5. When the device transitions to a low-power state, the framework does not call EvtInterruptDisable for the wake-capable interrupt. The framework does call EvtDeviceArmWakeFromS0 if the driver has provided one.
  6. When the device signals the wake interrupt, the framework calls the driver's EvtDeviceD0Entry callback routine.
  7. If the driver's EvtDeviceD0Entry callback returns success, the framework calls the driver's EvtInterruptIsr callback at passive level. Before the interrupt handler returns, it must silence the interrupt in the interrupt controller. If the driver returns a failure code from EvtDeviceD0Entry, the framework disconnects the interrupt and calls the driver's EvtInterruptDisable callback, if the driver has provided one.
  8. The framework calls the following wake event callback routines, if the driver has provided any:
  9. The framework continues with the normal power-up callback sequence, as described in Power-Up Sequence for a Function or Filter Driver.

You can use the !wdfkd.wdfinterrupt debugger extension to show whether a specific interrupt has been configured to be wake-capable.

Wake interrupt functionality cannot be used in conjunction with USB selective suspend.

 

 

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