IWDFIoTargetStateManagement::Start method

The Start method starts sending queued requests to a local I/O target.

Syntax


HRESULT Start();

Parameters

This method has no parameters.

Return value

Start returns S_OK if the operation succeeds. Otherwise, this method might return one of the error codes:

Return code	Description
HRESULT_FROM_NT (STATUS_INVALID_DEVICE_STATE)	The device has been removed.

This method might return one of the other error codes that Winerror.h defines.

Remarks

If your driver can detect recoverable device errors, you might want your driver to call IWDFIoTargetStateManagement::Stop to temporarily stop sending requests to the local I/O target, then later call Start to resume sending requests.

Additionally, if a driver calls IWDFUsbTargetPipe2::ConfigureContinuousReader to configure a continuous reader for a USB pipe, the driver's IPnpCallback::OnD0Entry callback function must call Start to start the reader.

Your driver must call Start and IWDFIoTargetStateManagement::Stop synchronously. After the driver calls one of these functions, it must not call the other function before the first one returns.

For more information about Start, see Controlling a General I/O Target's State in UMDF.

For more information about I/O targets, see Using I/O Targets in UMDF.

Examples

The following code example first shows how a driver can obtain the IWDFIoTargetStateManagement interface for a USB pipe object. The code example then shows how an IPnpCallback::OnD0Entry callback function can call Start, if the driver uses a continuous reader for the USB pipe.



    IWDFIoTargetStateManagement * m_pIoTargetInterruptPipeStateMgmt = NULL;

    IWDFUsbTargetFactory *  pIUsbTargetFactory = NULL;
    IWDFUsbTargetDevice *   pIUsbTargetDevice = NULL;
    IWDFUsbInterface *      pIUsbInterface = NULL;
    IWDFUsbTargetPipe *     pIUsbPipe = NULL;

    hr = m_FxDevice->QueryInterface(IID_PPV_ARGS(&pIUsbTargetFactory));
    if (FAILED(hr))
    {...}
    hr = pIUsbTargetFactory->CreateUsbTargetDevice(&pIUsbTargetDevice);
    if (FAILED(hr))
    {...}
    hr = pIUsbTargetDevice->RetrieveUsbInterface(0, &pIUsbInterface);
    if (FAILED(hr))
    {...}
    NumEndPoints = pIUsbInterface->GetNumEndPoints();
    for (UCHAR PipeIndex = 0; PipeIndex < NumEndPoints; PipeIndex++)
    {
        hr = pIUsbInterface->RetrieveUsbPipeObject(PipeIndex, &pIUsbPipe);
        if (FAILED(hr))
        {...}
        else
        {
            if (pIUsbPipe->IsInEndPoint())
            {
                if (UsbdPipeTypeInterrupt == pIUsbPipe->GetType())
                {
                    m_pIUsbInterruptPipe = pIUsbPipe;
                    hr = m_pIUsbInterruptPipe->QueryInterface(IID_PPV_ARGS(&m_pIoTargetInterruptPipeStateMgmt));
                    if (FAILED(hr))
                    {...}
                }
            }
        }
    } 

HRESULT
CMyDevice::OnD0Entry(
    __in IWDFDevice*  pWdfDevice,
    __in WDF_POWER_DEVICE_STATE  previousState
    )
{
...
    m_pIoTargetInterruptPipeStateMgmt->Start();
...
    return S_OK;
}

Requirements

End of support	Unavailable in UMDF 2.0 and later.
Minimum UMDF version	1.5
Header	Wudfddi.h (include Wudfddi.h)
DLL	WUDFx.dll